Nephritis, Interstitial

Introduction

Background

Παθησεις ΕΝΔΟΝΕΦΡΙΚΕΣ ΠΟΥ ΔΕΝ ΑΦΟΡΟΥΝ ΤΟ ΣΠΕΙΡΑΜΑ = ΔΙΑΜΕΣΟ ΣΩΛΗΝΑΡΙΑΚΕΣ

ΣΑΦΩΣ ΣΥΧΝΑ ΣΥΝΥΠΑΡΧΕΙ ΑΡΧΟΜΕΝΗ ΣΠΕΙΡΑΜΑΤΙΚΗ ΒΛΑΒΗ ΣΕ ΕΔΑΦΟΣ ΕΓΚΑΤΕΣΤΗΜΕΝΗΣ ΔΙΑΜΕΣΟΣΩΛΗΝΑΡΙΑΚΗΣ ΝΟΣΟΥ ΟΠΟΥ ΚΥΡΙΑΡΧΟΥΝ ΟΙ ΕΚΔΗΛΩΣΕΙΣ ΤΗΣ ΣΠΕΙΡΑΜΑΤΙΚΗΣ ΝΟΣΟΥ

ΤΑ ΑΙΤΙΑ ΚΑΙ Η ΠΑΘΟΦΥΣΙΟΛΟΓΙΚΟΙ ΜΗΧΑΝΙΣΜΟΙ ΤΗΣ ΔΙΑΜΕΣΗΣ / ΣΩΛΗΝΑΡΙΑΚΗΣ ΝΟΣΟΥ ΠΟΙΚΙΛΛΟΥΝ, Ο ΔΕ ΑΣΘΕΝΗΣ ΔΥΝΑΤΟ ΝΑ ΠΑΡΟΥΣΙΑΖΕΙ ΟΞΕΙΕΣ ΕΙΤΕ ΧΡΟΝΙΕΣ ΠΑΘΟΛΟΓΙΚΕΣ ΚΑΤΑΣΤΑΣΕΙΣ

ΕΚΘΕΣΗ ΣΕ ΦΑΡΜΑΚΑ – ΛΟΙΠΟΥΣ ΤΟΞΙΚΟΥΣ ΠΑΡΑΓΟΝΤΕΣ – ΒΑΡΕΑ ΜΕΤΑΛΛΑ – ΣΠΑΝΙΩΣ ΣΥΣΧΕΤΙΣΗ ΜΕ ΛΟΙΜΩΞΗ

Η ΠΛΕΟΝ ΤΥΠΙΚΗ ΕΙΚΟΝΑ ΕΞΟΡΜΑΤΑΙ ΑΠΟ ΑΝΟΣΟΛΙΓΙΚΗ ΦΛΕΓΜΟΝΗ

Tubulointerstitial diseases

Acute tubulointerstitial nephritis:

o Hypersensitivity reactions (eg, drugs, penicillins, sulfa drugs, nonsteroidal anti-inflammatory drugs [NSAIDs] most common)

o Immunologic diseases (eg, associated with lupus, Goodpasture syndrome)

o Acute transplant rejectiono Infections:

Bacterial (must be accompanied by obstruction or reflux)

Viral (eg, cytomegalovirus [CMV], hantavirus, HIV, hepatitis B)

Fungal (eg, histoplasmosis) Parasitic (eg, Leishmania, Toxoplasma)

Chronic tubulointerstitial nephritis:

o Drugs (eg, analgesics, lithium, cyclosporine, tacrolimus)1

o Heavy metals (eg, lead, cadmium, mercury)o Obstructive uropathy, nephrolithiasis, reflux diseaseo Immunologic diseases:

Lupus, Sjögren syndrome, primary glomerulopathies, sarcoidosis - A study by Maripuri et al found that out of 24 patients with primary Sjögren syndrome who also had renal impairment, biopsies revealed that 17 individuals had tubulointerstitial nephritis as the primary lesion behind their kidney dysfunction.2 Eleven of the 17 patients had the chronic form of this nephritis. The results, according to the investigators, support the notion that in patients with primary Sjögren syndrome, chronic tubulointerstitial nephritis is the most frequent cause of renal impairment found through kidney biopsy.

Vasculitis, antineutrophil cytoplasmic antibody (ANCA)–associated vasculitides, Wegener granulomatosis

Chronic transplant nephropathy

o Neoplasia (eg, myeloma, leukemia, amyloidosis)o Atherosclerotic kidney disease (ischemic) - Cholesterol

microembolismo Metabolic diseases (eg, hypercalcemia, cystinosis, potassium

depletion, nephropathy, hyperoxaluria)o Genetics (eg, Alport syndrome, medullary cystic disease)o Miscellaneous (eg, Balkan endemic nephropathy, Chinese

herb/aristolochic acid nephropathy)3,4

Pathophysiology

ΣΕ ΔΟΜΙΚΟ ΕΠΙΠΕΔΟ Η ΑΝΑΜΕΝΟΜΕΝΗ ΕΙΚΟΝΑ ΣΕ ΟΞΕΙΑ ΑΛΛΑ ΚΑΙ ΣΕ ΧΡΟΝΙΟ ΔΙΑΜΕΣΗ ΝΕΦΡΟΠΑΘΕΙΑ ΕΙΝΑΙ ΤΟ ΑΠΟΤΕΛΕΣΜΑ ΤΗΣ ΑΛΛΗΛΕΠΙΔΡΑΣΗΣ ΤΩΝ ΝΕΦΡΙΚΩΝ ΚΥΤΤΑΡΩΝ ΜΕ ΤΑ ΚΥΤΤΑΡΑ ΤΗΣ ΦΛΕΓΜΟΝΗΣ ΚΑΙ ΤΑ ΠΑΡΑΓΩΓΑ ΑΥΤΩΝ

Η ΚΥΤΤΑΡΙΚΗ ΚΑΤΑΣΤΡΟΦΗ ΣΥΝΕΠΑΓΕΤΑΙ ΤΗΝ ΠΑΡΟΥΣΙΑ ΑΝΤΙΓΟΝΩΝ ΣΕ ΤΟΠΙΚΟ ΕΠΙΠΕΔΟ, ΔΙΗΘΗΣ ΜΕ ΚΥΤΤΑΡΑ ΦΛΕΓΜΟΝΗΣ, ΕΝΕΡΓΟΠΟΙΗΣΗ ΠΡΟΦΛΕΓΜΟΝΟΔΩΝ ΚΑΙ ΧΗΜΕΙΟΤΑΚΤΙΚΩΝ ΚΥΤΤΟΚΙΝΩΝ ΜΕ ΤΕΛΙΚΗ ΕΚΒΑΣΗ ΟΧΕΙΑ ΕΙΤΕ ΧΡΟΝΙΟ ΝΕΦΡΙΤΙΔΑ

These cytokines are produced by inflammatory cells (ie, macrophages, lymphocytes) and also by the renal cells (ie, proximal tubule, vascular endothelial cells, interstitial cells, fibroblasts).

ΟΞΕΙΑ ΔΙΑΜΕΣΟΣ ΝΕΦΡΙΤΙΔΑ = ΣΩΛΗΝΑΡΙΑΚΗ ΚΑΤΑΣΤΡΟΦΗ / ΔΥΣΛΕΙΤΟΥΡΓΙΑ ΜΕ / ΑΝΕΥ ΝΕΦΡΙΚΗ ΑΝΕΠΑΡΚΕΙΑ

ΑΝΕΞΑΡΤΗΤΑ ΑΠΟ ΤΗΝ ΕΚΤΑΣΗ ΤΗΣ ΣΩΛΗΝΑΡΙΚΑΗΣ ΚΑΤΑΣΤΡΟΦΗΣ, Η ΝΕΦΡΙΚΗ ΔΥΣΛΕΙΤΟΥΡΓΙΑ ΚΑΤΑ ΚΑΝΟΝΑ ΒΕΛΤΙΩΝΕΤΑΙ / ΑΝΑΣΤΡΕΦΕΤΑΙ, ΑΝΤΑΝΑΚΛΩΝΤΑΣ ΤΗΝ ΑΝΑΓΓΕΝΗΤΙΚΗ ΙΚΑΝΟΤΗΤΑ ΤΩΝ ΣΩΛΗΝΑΡΙΩΝ ΜΕ ΑΝΕΠΑΦΗ ΒΑΣΙΚΗ ΜΕΜΒΡΑΝΗ

ΑΝΤΙΣΤΡΟΦΩΣ, Η ΧΡΟΝΙΟΣ ΔΙΑΜΕΣΗ ΝΕΦΡΙΤΙΔΑ ΧΑΡΑΚΤΗΡΙΖΕΤΑΙ ΑΠΟ :

o ΟΥΛΟΠΟΙΗΣΗ o ΙΝΩΣΗo ΣΩΛΗΝΑΡΙΑΚΗ ΑΤΡΟΦΙΑ

ΜΕ ΠΡΟΟΔΕΥΤΙΚΗ ΕΞΕΛΙΞΗ ΣΕ ΧΝΑ

ΜΗΧΑΝΙΣΜΟΙ ΟΞΕΙΑΣ ΔΙΑΜΕΣΗΣ ΝΕΦΡΙΤΙΔΑΣ :

1..ΑΝΤΙΔΡΑΣΗ ΥΠΕΡΕΥΑΙΣΘΗΣΙΑΣ ΣΕ ΦΑΡΜΑΚΑ

ΠΕΝΙΚΙΛΛΙΝΗ – ΦΣΑΦ – sulfa drugs

2..ΟΞΕΙΑ ΣΩΛΗΝΑΡΙΑΚΗ ΝΕΚΡΩΣΗ

ΑΠΟΦΡΑΞΗ ‘Η ΠΑΛΙΝΔΡΟΜΗΣΗ + ΛΟΙΜΩΞΗ

The kidney is remarkably resistant to structural damage in bacterial infections, and, in the absence of obstruction, damage from bacterial infection in the kidney parenchyma is extremely unlikely to occur.

Studies have revealed transforming growth factor beta (TGF β) as a major participant in fibrogenesis. TGF β favors accumulation of collagen and noncollagen basement membrane components by direct stimulation of production and by inhibiting matrix degradation enzymes such as collagenases and metalloproteinases.

Activation of nuclear transcription factors, such as nuclear factor kappa B (NF- �B) in injured kidney cells, with consequent transcription and release of proinflammatory cytokines into the interstitium, appears to be a major mechanism of chronic tubulointerstitial inflammation accompanying proteinuric kidney diseases.

Frequency

United States

Primary tubulointerstitial diseases, ie, diseases of the renal tubules and interstitium sparing the glomeruli, constitute 10-15% of all kidney diseases both in the United States and around the world.

International

In certain regions, such as the Balkans (ie, Yugoslavia, Bosnia, Croatia, Romania, Bulgaria), where endemic nephropathy is common, interstitial diseases may be more prevalent.3,4

Mortality/Morbidity

o Tubulointerstitial disease may progress to end-stage renal disease.

o An increased incidence of uroepithelial cancers is found among patients with analgesic nephropathy, aristolochic acid nephropathy, and Balkan endemic nephropathy.3,4

Race

Neither acute nor chronic tubulointerstitial diseases of the kidney demonstrate racial predilections. Lead nephropathy may be more common in black people because of socioeconomic factors.

Sex

Analgesic nephropathy is 5-6 times more common in women. This is generally attributed to women taking more analgesics than men. However, a greater sensitivity to the toxic effects of analgesics or differences in analgesic metabolism in women cannot be ruled out.

Age

All toxic nephropathies are related to the cumulative effects of toxic substances, particularly lead, and consequently are likely to be observed more frequently with advancing age.

However, this is highly variable.

For example, people with severe lead poisoning during childhood may present with chronic tubulointerstitial nephritis in early adult life.

Atherosclerotic and/or ischemic kidney disease is increasingly more common in elderly individuals.

Metabolic disorders, such as cystinosis, oxalosis, andhypercalcemia, can occur in younger individuals.

Clinical

History

History depends on whether the tubulointerstitial nephritis is acute or chronic.

Acute tubulointerstitial nephritis (general features)

ΤΥΠΙΚΗ ΕΝΑΡΞΗ = ΤΑΧΕΙΑ ΕΓΚΑΤΑΣΤΑΣΗ ΟΝΑ

ΚΑΤΑ ΚΑΝΟΝΑ ΕΝΤΟΣ ΗΜΕΡΩΝ ΑΠΟ ΤΗΝ ΕΝΑΡΞΗ ΕΚΘΕΣΗΣ ΣΤΟΤΟΞΙΚΟ ΠΑΡΑΓΟΝΤΑ

ΜΣΑΦ : ΜΕΤΑ ΑΠΟ ΕΚΘΕΣΗ ΜΗΝΩΝ

o ΕΞΑΝΘΗΜΑ o ΠΥΡΕΤΟΣo ΕΩΣΙΝΟΦΙΛΙΑo ΕΩΣΙΝΟΦΙΛΟΥΡΙΑo ΑΥΞΗΣΗ ΤΩΝ IgE

ΕΞΑΙΡΕΣΗ = rifampin, ΜΣΑΦ

ΗΠΙΑ ΔΙΑΜΕΣΗ ΝΕΦΡΙΤΙΔΑ

ΕΝΙΟΤΕ = ΕΞΑΝΘΗΜΑ + ΑΙΜΑΤΟΥΡΙΑ

ΥΠΟΥΛΗ ΕΓΚΑΤΑΣΤΑΣΗ ΣΩΛΗΝΑΡΙΑΚΗΣ ΔΙΑΤΑΡΑΧΗΣ

= [Fanconi syndrome : ΑΜΙΝΟΞΥΟΥΡΙΑ – ΓΛΥΚΟΖΟΥΡΙΑ –ΝΕΦΡΟΣΩΛΗΝΑΡΙΑΚΗ ΟΞΕΩΣΗ ]

ΠΡΩΤΕΙΝΟΥΡΙΑ = ΑΠΟΥΣΙΑΖΕΙ Ή ΕΙΝΑΙ ΗΠΙΑ

o ΟΥΡΙΝΑΛΥΣΗ = o ΜΙΚΡΟΣΚΟΠΙΚΗ ΑΙΜΑΤΟΥΡΙΑΣΤΕΙΡΑ ΠΥΟΥΡΙΑo ΜΕ / ΑΝΕΥ ΕΩΣΙΝΟΦΙΛΑ

ΑΝ ΚΑΙ Η ΚΛΙΝΙΚΗ ΕΙΚΟΝΑ ΕΙΝΑΙ ΤΥΠΙΚΗ ΚΑΤΑ ΚΑΝΟΝΑ ΔΙΑΓΝΩΣΗ ΤΙΘΕΤΑΙ ΜΟΝΟ ΜΕΤΑ ΑΠΟ ΒΙΟΨΙΑ

ΜΣΑΦ ΤΟΞΙΚΟΤΗΤΑ = ΒΑΡΕΙΑ ΠΡΩΤΕΙΝΟΥΡΙΑ, ΣΥΧΝΑ ΔΙΚΗΝ ΝΕΦΡΩΣΙΚΟΥ ΣΥΝΔΡΟΜΟΥ

Η ΑΜΕΣΗ ΔΙΑΚΟΠΗ ΤΟΥ ΤΟΞΙΟΥ ΠΑΡΑΓΟΝΤΑ, ΣΥΝΗΘΩΣ ΑΛΛΑ ΟΧΙ ΠΑΝΤΟΤΕ ΣΥΝΕΠΑΓΕΤΑΙ ΤΗΝ ΥΠΟΣΤΡΟΦΗ ΤΗΣ ΝΟΣΟΥ, ΚΑΠΟΤΕ Η ΝΟΣΟΣ ΕΠΙΜΕΝΕΙ ΕΒΔΟΜΑΔΕΣ ΠΡΙΝ ΤΗΝ ΕΝΑΡΞΗ ΒΕΛΤΙΩΣΗΣ

Although any drug can potentially cause a hypersensitivity reaction involving the kidney, the following are the most frequently implicated:

o Antibiotics (eg, penicillins, cephalosporins, sulfa drugs, quinolones)

o NSAIDso Diuretics (eg, thiazides, furosemide)o Allopurinolo Phenytoino Rifampino Interferon alfao Proton pump inhibitors

Acute tubulointerstitial nephritis caused by NSAIDs

This condition is more common in elderly people, perhaps because of the higher incidence of arthritic disorders in this population.

Acute allergic interstitial nephritis should not be confused with the acute vasomotor renal insufficiency that can occur in patients with preexisting underperfusion of the kidney.

A unique feature of allergic interstitial nephritis caused by NSAIDs is that patients may present with nephroticsyndrome. In such patients, massive proteinuria with hypoalbuminemia and edema are present in addition to the typical features of acute interstitial nephritis.

Findings on kidney biopsy show features of minimal change nephrosis in addition to the characteristic findings of interstitial nephritis

Antibiotic-induced acute tubulointerstitial nephritis

This form of nephritis is usually observed in the hospital setting during treatment of serious infections, within several days to weeks of initiation of antibiotic therapy.

Rash, eosinophilia, and eosinophiluria, as well as pyuria (sterile), hematuria, and modest proteinuria (usually <1 g/d), are common.

Unlike in NSAID-induced allergic interstitial nephritis, nephrotic range proteinuria is very rare.

If a renal biopsy is performed, eosinophils can be a component of the interstitial nephritis

Occasionally, ill-defined granulomas are present

Among antibiotics, rifampin is unique in that the interstitial nephritis generally occurs when the antibiotic is reintroduced after an interval.

Furthermore, the interstitial nephritis associated with it does not manifest with eosinophilia.

In some cases, rifampin-associated interstitial nephritis has been reported to show casts containing immunoglobulin light chains in tubular lumens without any evidence of myeloma in the patient.

Flulike symptoms, flank pain, hypertension, and oliguric acute renal failure are common.

In some patients, circulating antirifampin antibodies and immunoglobulin G (IgG) deposits along the tubular basement membranes have been reported.

Acute tubulointerstitial nephritis caused by miscellaneous agents

Infections with viral agents, bacteria, and fungi are occasionally associated with acute interstitial nephritis. Hantavirus, CMV, and HIV are common among the infectious agents associated with acute interstitial nephritis.

In HIV disease, acute interstitial nephritis is usually observed in conjunction with glomerular disease (ie, focal segmental glomerulosclerosis).

Parenchymal invasion by the virus is not always present, and other characteristic features, such as eosinophilia and fever, are usually absent.

Bacterial infection with renal parenchymal invasion is sometimes responsible for acute interstitial nephritis, but this is exceedingly rare in the absence of obstruction.

Other infections such as tuberculosis and histoplasmosis are also among the rare causes of acute tubulointerstitial nephritis and may be diagnostic challenges.

Chronic tubulointerstitial nephritis (general features)

The chronic form is an insidious disease and most probably represents the common final response pattern of the kidney to a variety of insults and agents

Important causes include analgesics; lead; drugs, including cyclosporine, cisplatin, and lithium; and metabolic disorders, notably hypercalcemia, potassium depletion, and hyperoxaluria.

Because of its insidious nature, chronic tubulointerstitial nephritis is often diagnosed incidentally on routine laboratory screening or evaluation of hypertension.

Patients are usually asymptomatic. Hypertension is common but not universal, and it is conspicuously absent in Balkan endemic nephropathy.

Clinical investigations may show modest elevation in serum creatinine, evidence of tubular dysfunction (ie, renal tubular acidosis), or Fanconi syndrome (ie, aminoaciduria, glycosuria, hypophosphatemia, hypouricemia). Proteinuria is usually mild, often less than 1 g/d.

In contrast to glomerular disease, a significant fraction of the protein is low molecular weight (eg, immunoglobulin light chains, beta2 microglobulin, lysozyme, peptide hormones).

These proteins are normally taken up by the proximal tubules and broken down there. Thus, in diseases predominantly involving tubular structures, decreased endocytosis of filtered proteins leads to the characteristic tubular proteinuria.

Findings on kidney biopsy in chronic tubulointerstitial nephritis usually show varying degrees of interstitial fibrosis, tubular atrophy, arteriolar sclerosis, and, occasionally, mononuclear cell infiltration (see image below).

Often, the findings are nonspecific and the etiology is not discernible from the biopsy; some diseases, such as sarcoidosis, show noncaseating granulomas, and, in viral diseases, immunostaining can yield clues to the cause.

In patients with suspected lead exposure, an ethylenediaminetetraacetic acid (EDTA) lead mobilization test or determination of tibial bone lead by radiographic fluorescence can confirm lead etiology.

Analgesic nephropathy1

Analgesic nephropathy is the most common category of chronic interstitial nephritis worldwide. This disorder occurs with long-term ingestion of combinations of phenacetin, aspirin, and caffeine or phenacetin-acetaminophen or NSAIDs and acetaminophen. In its most severe form, it is associated with papillary necrosis.

The amount of phenacetin-acetaminophen combination required to cause chronic interstitial nephritis has been estimated to be at least 2-3 kg over many years.

Although initially thought to be exclusively associated with phenacetin-containing combinations, all analgesics, including acetaminophen, aspirin, and NSAIDs, can cause analgesic-induced chronic tubulointerstitial nephritis.

Analgesic nephropathy is most common in women in the sixth and seventh decades of life who have a history of low back pain, migraine headaches, or other chronic musculoskeletal pain.

In some patients, a history can be elicited of episodes of :

o papillary necrosis, ie, o gross hematuria with o flank pain occasionally accompanied by o obstruction and o infection

Clinically, patients with analgesic nephropathy present with renal insufficiency, modest proteinuria, sterile pyuria, and anemia. Diagnosis can be supported by history of heavy analgesic use, and computer-assisted tomograms may reveal microcalcifications at the papillary tips.

Treatment is supportive and includes discontinuation of analgesic use. Long-term follow-up studies have shown progression to end-stage renal disease requiring dialysis, and increased incidence of uroepithelial cancers is also observed in patients with analgesic nephropathy.

Lithium nephropathy

Distal tubular dysfunction ie,

o polyuria, o concentrating defect, o down-regulation of aquaporin-2

occurs in up to 50% of patients receiving lithium.

Chronic interstitial nephritis occurs in a small subset of patients receiving long-term lithium therapy who have had repeated episodes of lithium toxicity with high serum levels.

Cyclosporine- and tacrolimus-induced nephropathy

These agents, although indispensable in the management of solid organ transplantation, can cause acute and chronic nephrotoxicity.

The mechanism appears to be dependent largely on the potent vasoconstrictive effects of these drugs. Chronic tubulointerstitial nephritis induced by cyclosporine or tacrolimus is common among patients receiving kidney, heart, liver, and pancreas transplants.

However, it is rare in bone marrow transplant recipients because they receive the drugs for a short time and generally at lower doses.

In renal transplant recipients, cyclosporine- or tacrolimus-induced chronic interstitial nephritis is similar to chronic rejection.

Because the pathophysiology of both is poorly understood, these conditions tend to be included under the generic term of chronic transplant nephropathy.

Most kidney transplant patients have a stable course with mild impairment of renal function. However, up to 10% of heart transplant recipients develop progressive renal insufficiency and eventually require dialysis.

Both cyclosporine and tacrolimus frequently cause hypertension and hyperkalemia.

Hypomagnesemia caused by renal magnesium wasting is also common in cyclosporine-treated patients.

Concomitant use of calcium channel blockers reduces nephrotoxicity.

Long-term use of cyclosporine has been associated with patchy interstitial fibrosis, usually in a striped pattern and with tubular atrophy.

Thrombotic microangiopathy might further contribute to both acute and chronic nephrotoxicity.

Lead nephropathy

Since antiquity, lead has been known to cause kidney disease and gout. In the modern industrialized world, lead is a ubiquitous environmental and occupational toxin and is an important cause of chronic tubulointerstitial nephritis and hypertension, mainly in urban poor communities and particularly among black people.

Children with severe lead poisoning can present with encephalopathy and acute renal failure with Fanconi syndrome. Because lead has a biologic half-life of several decades, if untreated by chelation, both intermittent acute poisoning and low-level environmental exposure result in chronic cumulative lead poisoning. The major consequence of chronic lead poisoning is chronic tubulointerstitial disease, usually in the third to fourth decades of life.

A common source of lead poisoning is leaded paint chipping in old urban tenements. Young childrenattracted to the sweet taste of the leaded paint may ingest or inhale dust particles containing lead and are at particular risk. In the industrial setting, welders, smelters, battery workers, painters, and restorers of old buildings, especially in poorly ventilated work environments, can be exposed to toxic amounts of lead.

Hypertension is almost always present, and, in the absence of appropriate testing or careful exposure history, lead nephropathy is often misdiagnosed as so-called hypertensive kidney disease. Patients with lead nephropathy tend to have disproportionately worse hyperuricemia compared to patients with other kidney diseases because of the unique effects of lead on urate metabolism, and, consequently, gout is common.

In retrospect, after careful investigation including the EDTA lead mobilization test, many patients presumed to have either gouty nephropathy or hypertensive nephrosclerosis are discovered to have lead nephropathy. Identification of the lead etiology in patients presumed to have gout nephropathy has cast doubt on the existence of this entity.

Obstructive uropathy

Obstruction of urinary outflow as observed in :

o prostate disease, o stone disease, o neoplasm, and o retroperitoneal fibrosis

among others, can cause chronic tubulointerstitial disease.

Modest proteinuria and hyperkalemic renal tubular acidosis are common.

Vesicoureteral reflux disease, usually congenital, characteristically results in focal glomerulosclerosis with nephrotic syndrome and a prominent tubulointerstitial component in adult life even if the reflux has been corrected early.

Superimposed infection and pyelonephritis often complicate obstruction.

Recurrent urinary tract infection itself can cause ammonium magnesium phosphate stones, further aggravating tubulointerstitial disease and perpetuating infection.

Similarly, papillary necrosis and infection may complicate the course and may lead to acute pyelonephritis with fever, flank pain, hematuria, and, especially in elderly patients, urosepsis.

Atherosclerotic kidney disease

As life expectancy increases, atherosclerotic disease of the kidney is emerging as a major category of chronic tubulointerstitial nephropathy.

Unfortunately, no unanimity on nomenclature exists among experts, and kidney disease in this category is variably termed is :\

o Ιchemic nephropathy,o renovascular disease, and o nephrosclerosis

In all likelihood, cases of so-called hypertensive kidney disease or hypertensive nephrosclerosis belong in the category of atherosclerotic kidney disease.

Lack of appropriate diagnosis can explain the discrepancy in the incidence of kidney disease in hypertensive populations in Europe and the United States.

In Europe, kidney disease is found in only about 1% of hypertensive populations, while in the United States 30% of all end-stage disease requiring dialysis is attributed to hypertensive kidney disease.

Atherosclerotic kidney disease is typically observed in elderly white males who smoke, but it is by no means confined to this population.

Many individuals with dyslipidemia and other atherosclerotic phenomena, such as coronary artery disease, carotid artery disease, and peripheral arterial disease, are prone to involvement of renal arteries, regardless of age.

Often, these patients have hypertension, not necessarily severe, with elevated serum creatinine and urea nitrogen and proteinuria, 1-2 g/d. The course of progression of the kidney disease is usually slower than in patients with glomerular diseases such as diabetic nephropathy.

Diagnosis can usually be made clinically, and radiologic investigations, such as duplex scanning of the renal arteries, digital subtraction angiography, or magnetic resonance imaging, reveal atherosclerotic stenosis of the renal arteries.

Kidney biopsy is seldom necessary and, if performed, shows nonspecific changes of chronic tubulointerstitial nephritis, ie, tubular atrophy, fibrosis, and arterial or arteriolar sclerosis with paucity of cellular infiltration.

Because these patients tend to have atherosclerotic complications, they are likely to experience multiple contrast

procedures and hence are at risk for acute recurrent contrast nephropathy, which can accelerate progression to end-stage renal disease.

No specific therapy is available, but good control of hypertension, cessation of smoking, and vigorous control of dyslipidemia with diet and with hepatic 3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors are expected to result in improved outcomes.

Cholesterol microembolic disease and nephropathy

This is a unique syndrome that has been recognized in the setting of catheter procedures involving vasculature above the renal arteries, such as coronary angiography, although it can occur in patients on anticoagulation; it can even spontaneously.

The pathophysiology is destabilization of atheroma plaques, either during catheter manipulation or spontaneously, resulting in showering of cholesterol crystals downstream and eventual lodging of needle-shaped cholesterol crystals in small arterioles within the kidney vessels (see images below).

Microemboli can also occur in the central nervous system and retinal arteries (called Hollenhorst plaques). In the extremities, distal vessel emboli may result in small superficial skin infarcts (scabs).

More extensive cholesterol microembolization to the extremities can result in the characteristic livedo reticularis appearance in the lower extremities.

Oddly, some patients have other systemic signs and symptoms, such as low-grade fever, leukocytosis, eosinophilia, elevated sedimentation rate, and hypocomplementemia.

Cholesterol microembolism usually causes acute renal failure of varying degrees, with some spontaneous improvement in renal function but often with permanent residual renal damage.

Kidney biopsy during the acute phase shows the characteristic needle-shaped clefts caused by the cholesterol crystals within the small- and medium-sized arteriolesaccompanied by patchy tubulointerstitial nephritis with mild mononuclear cellular infiltration.

No effective treatment for this disorder is available.

Metabolic disorders and nephropathy

o Hypercalcemia, o chronic potassium depletion, and o cystinosis

can lead to chronic tubulointerstitial nephritis.

Hypercalcemia is the most common cause.

Chronic hypercalcemia can occur in :

o primary hyperparathyroidism, o sarcoidosis, o multiple myeloma, and o other neoplasms (particularly with bone metastases) and

in vitamin D intoxication.

Even transient hypercalcemia can lead to chronic renal insufficiency; renal involvement is mostly confined to the distal tubular structures.

Clinically, polyuria and concentrating defect are common.

During acute hypercalcemia, urinary concentrating defect can lead to dehydration and may aggravate acute renal failure.

Radiologic examinations may reveal nephrocalcinosis, and renal stone formation can be a complicating factor in hypercalcemia.

Balkan endemic nephropathy3,4

This is an endemic kidney disease confined to well-defined discrete settlements located along the Danube River and its tributaries.

The caseload of patients is particularly heavy in the Balkans (ie, Bosnia, Croatia, Yugoslavia, Romania, Bulgaria). The disease occurs in individuals, autochthonous or immigrant, who have resided in the endemic regions for at least 15-20 years and does not occur among residents who move to nonendemic areas.

Thus, the evidence implicates environmental factor(s), but no definitive agent or factor has been identified yet.

Typically, patients are nonhypertensive and have disproportionately profound anemia.

Patients are identified easily in the endemic regions by checking for tubular proteinuria. Beta2 microglobulinuria has proved particularly useful in identifying cases and has been proposed and used as a marker of the disease.

Because a major criterion to identify the disease is residency in the endemic region, whether similar kidney diseases occur in other parts of the world is not known.

Most patients eventually develop end-stage renal disease and require dialysis. Up to 40% of patients develop upper urinary tract uroepithelial tumors.

Chinese herb/aristolochic acid nephropathy

Chronic progressive tubulointerstitial nephritis has been observed in many countries among patients using Chinese herbal medicines for weight reduction.

Most of these cases have been attributed to herbs containing aristolochic acid.

The pathophysiology of nephrotoxicity is not well understood. Renal biopsies have shown severe interstitial fibrosis.

Physical

A thorough physical examination may provide clues to the diagnosis eg :

o fever, o rash in acute tubulointerstitial nephritis, o livido reticularis and o Hollenhorst plaques in the optic fundi in atheroembolic

disease

but, in most patients, no characteristic findings exist.

Some patients present with hypertension, although others may be normotensive or hypotensive (eg, Balkan endemic nephropathy).5

o Acute allergic tubulointerstitial nephritis:Physical examination in acute tubulointerstitial nephritis may show a rash accompanying renal findings. However, rash is highly variable. Although the presence of rash can be supportive evidence of an allergic etiology of an acute renal insufficiency, its absence is not useful in ruling out acute allergic interstitial nephritis.

o Cholesterol microembolic disease: In cholesterol microembolic disease, eyeground examination may reveal the characteristic cholesterol crystals, also termed Hollenhorst plaques, in retinal vessels, which can support the diagnosis. Similarly, the presence of small skin infarcts or scabs, especially on or between the toes or fingers, is a helpful clue to cholesterol microembolism. Sometimes, particularly after displacement of a large aortic plaque, marked ischemia of the lower extremities yields a bluish-purplish discoloration (ie, livedo reticularis) of the feet or lower portions of legs.

o Atherosclerotic (ischemic) kidney disease:Evidence for other atherosclerotic disease, such as carotid or inguinal bruits, may be clues to so-called atherosclerotic kidney disease, particularly in elderly white males who smoke.

Causes

Acute allergic interstitial nephritis: Any drug can cause an acute allergic reaction involving the kidneys. Drugs most commonly associated with acute allergic nephritides are listed in History.

Cholesterol microembolic disease:Underlying atherosclerotic disease, dyslipidemia, and smoking are conditions commonly associated with this disorder. Catheter manipulations above the levelof the renal arteries or anticoagulation in a patient with atherosclerosis can trigger cholesterol microembolic disease.

Balkan endemic nephropathy: Epidemiology and natural history clearly implicate environmental factors in the pathophysiology of this disease. Lead contamination of food has been considered but ruled out as a cause. Some studies have implicated a fungal toxin, called "ochratoxin," which can grow in moist grains in storage and which has been shown to cause a similar kidney disease in pigs in several central European countries. However, most experts agree that the evidence for its role in this endemic nephropathy is weak.

Lead nephropathy: Environmental and occupational exposure to lead can cause chronic tubulointerstitial nephritis. Occupations in welding, smelting, the battery industry, and mining have all been responsible for lead nephropathy cases. Environmental exposure from leaded gasoline is decreasing because the use of leaded gasoline has ceased in the United States. Sporadic exposure is still observed, particularly among children living in deteriorating housing in urban areas. Rarely, lead poisoning can be observed among individuals who consume moonshine whiskey and those who drink beverages from imported ceramics painted with leaded glaze.

Obstructive uropathy: A variety of causes contribute to obstructive uropathy. Prostate disease in elderly males and pelvic or colonic tumors involving both ureters in both sexes can cause obstructive uropathy. Nephrolithiasis, with or without urinary tract infection, may also cause obstructive uropathy. Radiation to the pelvic area and some drugs, such as methysergide, can cause retroperitoneal fibrosis and obstruction.

Chinese herb/aristolochic acid nephropathy

o Aristolochic acid was recognized as a potent nephrotoxin that can cause rapidly progressive interstitial fibrosis and end-stage renal disease in young women using a Chinese herb as part of a slimming regimen in Belgium in early 1990s.

o Since then, many other cases of so-called Chinese herb (CH) nephropathy have been reported from around the world. CH

nephropathy may not be an appropriate name for the disease, however, because aristolochic acid can be present in herbal medicines from any country. The term aristolochic acid nephropathy (AAN) more accurately characterizes this form of toxic nephropathy.

o Another interesting feature of AAN is its association with uroepithelial cancers reminiscent of Balkan nephropathy. Aristolochic acid not only can trigger severe renal fibrosis but also can cause oncogene mutations that can explain the high incidence of renal cancer with this type of interstitial nephritis. Patients have also been found to have abnormal function of p53, a known tumor suppressor gene.

Differential Diagnoses

Acute Renal FailureGlomerulonephritis, AcuteUrinary Tract Obstruction

Other Problems to Be Considered

Radiation nephritisToxic nephropathies

Workup

Laboratory Studies

Complete blood cell count with differential:

Eosinophilia, when present, can be very helpful. However, this is neither specific nor sensitive enough to establish the diagnosis.

Although the true incidence of eosinophilia in acute tubulointerstitial nephritis is unknown, it is estimated to be present in approximately half of patients.

Unfortunately, the absence of eosinophiluria does not rule out the diagnosis, and it can be observed in other diseases, including :

o cholesterol microembolism, o urinary tract infections, o parasitic disorders, and o glomerulonephritis

Typically, eosinophilia is absent in AIN-induced by NSAIDs.

Blood chemistry: A complete set of chemistries, including BUN and serum creatinine, provides information on whether renal insufficiency exists.

A low bicarbonate level (total carbon dioxide <24-23 mEq/L) may indicate acidosis.

Low serum potassium levels may indicate a proximal tubular disorder, and

elevated serum potassium levels with a low bicarbonate level may indicate type 4 renal tubular acidosis, which can be

observed with lead nephropathy and NSAID-induced analgesic nephropathy, among other conditions.

Urinalysis: Urinalysis may reveal :

o proteinuria,o hematuria, and o the presence of white cells, o with or without bacteria

A microscopic analysis of urine sediment may reveal :

o casts, o white cells, o eosinophils, ando crystals.

If allergic interstitial nephritis is suspected, send a cytospin specimen to determine if eosinophils are in the urine.

In NSAID-induced AIN, eosinophiluria is usually absent.

Imaging Studies

Ultrasonography: This noninvasive technique is extremely helpful in identifying hydronephrosis in obstructive disease, as well as calculi in stone disease. Both radiolucent and radiopaque stones can be visualized using ultrasonography.

A combination of ultrasonography and flat plate kidney, ureter, and bladder (KUB) radiography is helpful in workup and identification of radiopaque versus radiolucent stones.

Normal kidney size by ultrasonographic examination generally favors but does not prove a diagnosis of acute (thus potentially reversible) kidney disease. In contrast, small (shrunken) kidneys with increased echogenicity indicate chronic and irreversible kidney disease.

Computer-assisted tomography (CT) scanning:This technique provides information similar to ultrasonographic scanning in the workup of kidney disease, generally with greater resolution. However, an ultrasonographic examination is sufficient in most kidney diseases. A high-resolution scan showing microcalcifications in renal papillary tips can be very helpful in diagnosis of analgesic nephropathy. The kidneys may be very small in Balkan endemic nephropathy and aristolochic acid nephropathy.

Intravenous pyelography: Once widely used, this technique seldom plays a role in the workup of kidney diseases in modern medicine. In many instances, similar information can be obtained by ultrasonography without exposing the patient to potentially nephrotoxic contrast dye.

Gallium scanning:

Findings on gallium scanning have been reported to be confirmatory in the diagnosis of acute interstitial nephritis.Thus, a negative finding helps to rule out this diagnosis. However, findings on this test have proved to be too nonspecific, except as a confirmatory tool in suspected cases.

Other Tests

EDTA lead mobilization test

Consider the possibility of lead nephropathy in patients presenting with chronic renal insufficiency, hypertension, and gout. In the absence of documented episodes of acute symptomatic lead poisoning, medical history is not reliable in ascertaining the lead etiology in patients presenting with chronic tubulointerstitial nephritis.

Diagnosis of lead nephropathy requiresestimation of cumulative body stores of lead by either EDTA lead mobilization test or by determination of bone lead content by radiographic fluorescence.

EDTA lead mobilization test is performed by measuring 24-hour urine lead excretion after intravenous or intramuscular administration of 2 g EDTA (calcium disodium versenate).

Excretion of more than 0.6 g of lead per 24 hours is considered an abnormal finding.

Blood lead levels, although elevated during acute or recent exposure, are not very helpful in the evaluation of chronic lead poisoning.

During acute exposure, lead is concentrated in the red blood cells and later extracted to tissues and bone as the red cells senesce.

Kidney biopsy is not diagnostic of lead etiology either and shows nonspecific changes such as interstitial fibrosis, tubular atrophy, and vascular sclerosis, findings common to tubulointerstitial nephritides of other etiologies. Body burden of lead and bone lead concentration can be reduced by extended chelation treatment using EDTA (versenate).

Quantitative determination of urine protein may be helpful.

Low-molecular weight proteins, such as beta-2 microglobulin, retinol binding protein (RBP), alpha-1 microglobulin, and immunoglobulin light chains, are increased in chronic tubulointerstitial nephritides.

Beta-2 microglobulinuria has been found helpful in the diagnosis of Balkan endemic nephropathy and cadmium nephropathy.

Procedures

Kidney biopsy: Kidney biopsy is the definitive test for diagnosing acute allergic interstitial nephritis, particularly in cases where clinical diagnosis is difficult. The differential diagnosis of acute tubulointerstitial nephritis encompasses multiple etiologies, including acute tubular necrosis, acute, vasculitis, and atheroembolic disease. Therefore, consider kidney biopsy when diagnosis is not obvious. Kidney biopsy shows mononuclear and often eosinophilic cellular infiltration of the renal parenchyma with sparing of the glomeruli (see second and third images below). Sometimes, interstitial changes such as fibrosis and atrophy are also present.

Acute cellular infiltration, particularly with eosinophilia, can be diagnostic of acute allergic interstitial nephritis (see first five images below). In cholesterol microembolism in the kidney, the

finding of a characteristic needle-shaped cleft in medium- or small-sized renal arterioles is diagnostic (see sixth and seventh images below). Chronic tubulointerstitial nephritis is characterized by tubular atrophy, fibrosis, and patchy infiltrate of mononuclear cells

Treatment – Medical Care

Treatment of acute tubulointerstitial nephritis

In most cases, cessation of the offending agent results in quick recovery and complete resolution of the renal disorder, although some patients progress to chronic renal insufficiency.

If no sign of improvement is observed within a few days of discontinuation of the offending agent, consider therapy with steroids.

Although controlled trials are lacking, many authors suggest using prednisone at relatively high doses, eg, 1 mg/kg for 4-6 weeks, with rapid tapering of the dose. This intervention may improve the outcome, speeding renal recovery and reducing the requirement for dialysis.

Treatment of chronic tubulointerstitial disease:

Treatment depends on the etiology and generally consists of supportive measures, such as :

o adequate blood pressure control and o management of anemia

Treatment of lead nephropathy

Chelation therapy is of proven value and must be implemented in acute lead poisoning. Although the oral chelating agent succimer (Chemet) has proved highly successful in treating children, it has not been widely used in adults. Nevertheless, it appears effective in reducing body lead stores.

Chelation therapy with EDTA may slow progressive renal insufficiency in patients with mild lead intoxication. Several studies from Taiwan have shown that chelation therapy in patients with modest increases in body lead burden (ie, 80-600 µg of lead) significantly slowed and/or reversed the rate of decline in the glomerular filtration rate (GFR) compared to placebo.

This was found in both diabetics and nondiabetics.6,7Given

that these studies took place in Taiwan, it is difficult to generalize these results. Further study is needed before this treatment can be recommended.

Because no effective therapy reverses the long-term consequences of lead poisoning, the best therapy is prevention and awareness of potential environmental and occupational sources for lead exposure.

In patients with established lead nephropathy, treatment consists of management of hypertension, gout, and chronic renal insufficiency.

Many patients with lead nephropathy progress to end-stage kidney failure and require dialysis.

Treatment of cyclosporine/tacrolimus induced renal failure:

Treatment includes reducing cyclosporine/tacrolimus doses and target trough levels.

Discontinuing these medications and/or switching to other immunosuppressives (eg, rapamycin), especially in those with more advanced renal failure, should also be considered.

Diet

Hypertensive patients should be on a low-sodium diet. For all patients with early renal disease, recommend general guidelines for a healthy diet, ie, low-fat (low-cholesterol) diet rich in fresh fruits and vegetables such as the dietary approaches to stop hypertension (DASH) diet.

Medication

For acute allergic interstitial nephritis, if no spontaneous recovery in renal function is observed after cessation of the offending agent, implementing a short course of steroid therapy is generally recommended. No controlled studies exist on the effect of corticosteroids. Therefore, no well-defined dosage and duration exist. Most practitioners recommend a relatively high dose (eg, 1 mg/kg prednisone) with a rapidly tapering regimen within several weeks.

Glucocorticoids

Immunosuppressants for treatment of autoimmune disorders.

Prednisone (Sterapred)

Has anti-inflammatory properties and causes profound and varied metabolic effects.

Modifies the body's immune response to diverse stimuli.

o May decrease inflammation by reversing increased capillary permeability and

o suppressing PMN [= PML = polymorphonuclear leukocytes ] activity. o Stabilizes lysosomal membranes and o suppresses lymphocytes and antibody production

Adult

0.5-2 mg/kg/d PO, taper as condition improves; single am dose safer for long-term use, but divided doses have greater anti-inflammatory effect

o Coadministration with estrogens may decrease prednisone clearance;

o concurrent use with digoxin may cause digitalis toxicity secondary to hypokalemia;

o phenobarbital, phenytoin, and rifampin may increase metabolism of glucocorticoids (consider increasing maintenance dose);

monitor for hypokalemia with coadministration of diuretics

Precautions

Abrupt discontinuation of glucocorticoids may cause adrenalcrisis;

hyperglycemia, edema, osteonecrosis, myopathy, peptic ulcer disease, hypokalemia, osteoporosis, euphoria, psychosis, myasthenia gravis, growth suppression, and infections may occur with glucocorticoid use

Chelating agents

These agents promote the excretion of lead.

Succimer (Chemet)

Metal chelator, analog of dimercaprol. Used in lead poisoning.

Particularly useful in children with lead blood levels >45 mcg/dL.

Approved for chelation therapy in children for lead poisoning. Its value in chronic lead nephropathy is not established.

Adult

10 mg/kg PO q8h for 5 d, followed by 10 mg/kg PO q12h for 14 d; repeat dosing may be necessary

Precautions

Renal or hepatic impairment; to prevent toxicity, patients should be well hydrated

Edetate calcium disodium (Calcium

Disodium Versenate)

For lead chelation. Only the calcium disodium preparation should be used. In the context of this article, use of this medication is confined to testing, ie, to perform the EDTA lead mobilization test for diagnosing lead etiology of chronic tubulointerstitial nephritis. Extended therapy to reduce body lead stores may possibly be beneficial.

Adult

EDTA lead mobilization test: 2 g IV/IM;

for IV, dilute with 500 mL of D5W or 0.9% NaCl and infuse over 8-12 h;

if IM used, mix with 5 mL of 2% lidocaine to avoid pain at injection site

Pediatric

Administer as in adults; not to exceed 1 g/d

Follow-upFurther Inpatient Care

Patients with acute renal failure or with serious electrolyte or acid-base disorders may require inpatient care until stabilization or resolution.

Further Outpatient Care

Provide patients with acute interstitial nephritis with follow-up care until resolution.

Patients who do not recover renal function and those with chronic tubulointerstitial nephritis should receive long-term follow-up care to ensure that :

o optimal control of blood pressure is achieved and o to protect kidneys from further potentially nephrotoxic

therapies and/or interventions

Deterrence/Prevention

o Allergic interstitial nephritis: Early recognition and prompt discontinuation of the offending drug are helpful.

o Lead nephropathy: Implement environmental measures, such as removal of lead from indoor paint and gasoline, and eliminate other sources of exposure. Use caution with imported ceramics, particularly if glazed

Complications

o Hypertension may complicate any renal disease, but not all cases of interstitial renal disease are associated with hypertension (ie, Balkan endemic nephropathy, acute allergic interstitial nephritides).

o Electrolyte and acid-base disorders may be observed.o Chronic tubulointerstitial disease may progress to end-

stage renal disease, requiring dialysis or transplantation

Prognosis

o Allergic interstitial nephritis: Most patients recover renal function upon cessation of the offending agent.

o Cholesterol microembolic kidney disease:Often, some spontaneous improvement in renal function occurs after the embolic event. Complete resolution of renal insufficiency is rare, however.

o Chronic tubulointerstitial nephritides:Although the natural history of these diseases varies depending on the etiology, most chronic tubulointerstitial renal disease eventually progresses to end-stage renal disease. However, the rate of progression is generally believed to be much slower in tubulointerstitial nephritis compared to glomerular diseases.

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Allergic interstitial nephritis: Make sure to obtain a thorough history of previously documented drug allergies before prescribing a new drug.

MultimediaMedia file 1: Kidney biopsy. This is an example of acute interstitial nephritis. The renal cortex shows a diffuse interstitial, predominantly mononuclear, inflammatory infiltrate with no changes to the glomerulus. Tubules in the center of the field are separated by inflammation and edema, as compared with the more normal architecture in the right lower area (periodic acid-Schiff, 40 X).

Media file 2: Kidney biopsy. Shown here is an example of acute interstitial nephritis. The diagnosis is based on the active inflammatory infiltrate on the right with unaffected glomeruli. Interstitial edema and fibrosis are present on the left side of the field, where some tubules show thickened basement membrane (hematoxylin and eosin, 20 X).

Media file 3: Kidney biopsy. This image shows acute interstitial nephritis. The interstitium is expanded by mononuclear inflammatory infiltrate and edema. Acute tubular damage is present; some tubules are distended and contain granular casts (hematoxylin and eosin, 40 X).

Media file 4: Kidney biopsy in interstitial nephritis. Acute crescentic glomerulonephritis. The glomerular tuft is compressed by the proliferation of epithelial cells, forming a crescent. The interstitium shows mononuclear inflammatory infiltrate and edema (periodic acid-Schiff, 40 X).

Media file 5: Kidney biopsy. This image shows acute interstitial nephritis. The mononuclear inflammatory infiltrate contains abundant eosinophils, suggesting an allergic etiology. Severe tubular damage is observed (hematoxylin and eosin, 40 X).

Media file 6: Kidney biopsy. This image shows acute interstitial nephritis. The inflammatory infiltrate forms an ill-defined granuloma, suggesting allergic or infectious etiologies. A partially destroyed tubule is present (periodic acid-Schiff, 40 X).

Media file 7: Kidney biopsy. This image shows chronic tubulointerstitial nephritis. The interstitium is expanded by fibrosis, with distortion of tubules and periglomerular fibrosis. Glomeruli do not show pathologic changes (hematoxylin and eosin, 20 X).

Media file 8: Kidney biopsy in interstitial nephritis. This image shows a cholesterol microembolism. The 2 arterioles in the center are occluded by elongated crystals (hematoxylin and eosin, 20 X).

Media file 9: Kidney biopsy in interstitial nephritis. This image shows a cholesterol microembolism. The arteriole in the center of the field has a thickened wall. The lumen is occluded by elongated spaces, corresponding to dissolved crystals surrounded by cellular reaction. The 2 glomeruli flanking the arteriole are sclerotic and hardly recognizable (hematoxylin and eosin, 40 X).