NOTES AND LETTERS

Noncontamination of Proteolipid Protein Preparations by MBP Marjorie B. Lees, PhD, and Franca Cambi, MD

Trotter and Clark [ 4 ] have recently reported contamination of their proteolipid protein preparations with myelin basic protein (MBP) and have raised the possibility that the re- ported effects of immunization with proteolipid apoprotein could be due to the presence of MBP. We have carefully considered this problem for many years and conclude that, in our hands, preparations obtained as described in our papers 11, 27 are devoid of detectable amounts of MBP. Our evi- dence follows.

As stated in the original report El], our electroblot anal- yses would have detected as little as 0.008% MBP. No MBP was detected in the single apoprotein preparation used in those immunization studies. Subsequently, in preparations done according to a different procedure we were also unable to detect MBP by electroblot analysis. The isolation procedure used by Trotter and Clark differs from ours and apparently uses myelin as the starting ma- terial. Their evidence for MBP contamination is thus ap- plicable only to their preparation. For study of the biological effect of small amounts of MBP, each of six rabbits was immunized with 200 ng of MBP, which is twice the amount of MBP that would be detectable with electroblot analysis. Three animals were killed at 6 months. The others were boosted with 100 ng of MBP and killed 12 months later. None of these ani- mals showed clinical or histological evidence of experi- mental allergic encephalomyelitis. The possibility that the proteolipid protein might enhance the encephalitogenic activity of threshold doses of MBP was addressed in a study using Hartley guinea pigs. N o effect was noted (Lees, Cambl, and Sobel, unpublished data, 1983). The possibility that small amounts of peptides derived from MBP are present in proteolipid protein preparations cannot be ruled out directly. However, we have prelimi- nary evidence that a synthetic peptide based on the se- quence of the proteolipid protein produces clinical dis- ease with marked inflammation and demyelination. If this evidence can be confirmed, it will rule out definitively that the observed effects are due to MBP contamination.

We did not report the results of'the radioimmunoassay for MBP on our preparations because the data suggested MBP levels that could easily be detected by gel electrophoresis. Furthermore, 50 to 75% of the proteolipid preparation bound to an MBP antibody affinity column. Clearly, both of these results represent artifacts. These observations led us to carry out extensive studies to characterize the effects of pro- teolipids and lipids on the radioimmunoassay for MBP [3]. We found that the addition of proteolipid apoprotein to known amounts of MBP standard resulted in a 70% de- crease to a 200% increase in the apparent amounts of MBP

present, depending on the amount of apoprotein added. Nonneural apoproteins had similar, although less marked, effects. Clearly, the radioimmunoassay for MBP must be interpreted critically when applied to the isolated apoprotein.

Finally, 60 to 100% of rabbits immunized with bovine proteolipid apoprotein develop clinical and histological evi- dence of a chronic encephalomyelitis; this does not appear to be a consequence of contamination from MBP.

E. K. Shriuer Center 200 Trapelo Rd Waltbam, M A 02254

References 1. Cambi F, Lees MB, Williams RM, Macklin WB: Chronic experi-

mental allergic encephalomyelitis produced by bovine proteolipid apoprotein: immunological studies in rabbits. Ann Neurol

2. Lees MB, Sakura JD: Proteolipids. In Marks N, Rodnight R (eds): Research Methods in Neurochemistry, Vol 4. New York, Plenum, 1979, pp 354-370

3. Macklin WB, Lees MB, Cohen SR, et al: Hydrophobic com- pounds interfere in radioimmunoassay for basic protein in my- elin. Clin Chem 27:742-744, I981

4. Trotter JL, Clark HB: Contamination of proteolipid protein with basic protein. Ann Neurol 16:s 14, 1984

13:303-308, 1983

Hvbertensive Eiiephalopathy : Diffuse Reversible White Matter CT Abnormalities Marc Fisher, MD,' Bernard Maister, MB, ChB (Cape),' and Richard Jacobs, MDt

Hypertensive encephalopathy (HE) constitutes an acute medical emergency characterized by headache, confusion, delirium, seizures, and papilloretinal edema 181. The syn- drome has declined in incidence with the widespread use of antihypertensive therapy. The pathogenesis is unsettled but several mechanisms, including diffuse vasospasm, widespread small vessel occlusion, and cerebral edema, have been pro- posed 11, 2, 117.

A 30-year-old white man complained of difficulty concen- trating, focusing his eyes, and a mild frontal headache for the previous 24 hours. His past history included tophaceous gout, chronic renal failure, and hypertension. The patient was a high school graduate who was unemployed because of gouty arthropathy. His family stated his mental functioning had been normal until the acute changes began. Chronic ambulatory peritoneal dialysis had been instituted three weeks earlier. Medications on admission included colchicine, hydralazine, prednisone, allopurinol, and atenolol, and all predated the recently instituted peritoneal dialysis.

General physical examination findings were normal aside from tophaceous gout and an atrophic right arm as the result of disuse. Blood pressure (BPI was 2401150 mrn Hg, pulse

268

A

(A) Initial computed tomographic (CT) scan demonstrating dq- fuse white matter hypodensity, ventricukzr compression, and ob- literation of su l i . (B) Follmu-up scan six days after admission demonstrating improvement in the white matter and compressive changes. (C) Normal CT scan three weeks afer presentation.

B

80, respirations 18, and temperature 37°C. Mental status examination showed him to be alert and cooperative with a short attention span. Recent memory was 1 of 3 objects at one minute. His remote memory was poor as was his calcula- tion ability. He was oriented to person, place, and time. There was righdleft confusion but no somatoagnosia. Cranial nerve examination findings were normal and there was no papilledema. A few fluffy exudates but no hemorrhages were seen over both retinas. The rest of the neurological examina- tion was unremarkable.

Admission laboratory studies included a normal complete blood cell count, urinalysis, and electrolyte concentrations. The following measurements were made: creatinine, 10.9 mg/dl; blood urea nitrogen (BUN), 66 mg/dl; and calcium, 7.9 mg/dl. Lumbar puncture revealed an opening pressure of 360 mm H20 with no cells and a protein content of 22 mg/ dl. Monospot and Epstein-Barr virus titers were negative as were subsequent cerebrospinal fluid viral cultures. An elec- troencephalogram (EEG) showed generalized delta activity, while somatosensory and visual evoked responses were within normal limits. Computed tomographic (CT) scan showed a diffuse low density within the white matter as seen in Figure, A.

A nitroprusside drip lowered his BP and by the third day it stabilized at a baseline of 150-160/80-90 mm Hg. As the BP fell, his mental status improved. BUN and creatinine

C

Annals of Neurology Vol 18 No 2 August 1985 269

values remained at admission levels. By the seventh hospital day, he had regained his normal mental functioning. A CT scan on day 6 showed improvement in the white matter low- density changes (Figure, B). A CT scan three weeks later was within normal limits (Figure, C).

Our patient satisfies accepted criteria for the diagnosis of HE [4]. The lack of papilledema is uncommon but has been described in otherwise typical cases 15). The initial CT pic- ture of diffuse white matter hypodensity with sulcal and ven- tricular compression is compatible with diffuse white matter edema [7) . The CT abnormalities improved within six days and resolved completely within several weeks. Furthermore, Rail and Perkins f9) described similar CT changes in a pa- tient who had HE with papilledema. Kendall and associates 161 also described a diffuse white matter low density in single scans of two patients with HE but omitted clinical details. Gaitz and Bamford [ 3 ] reported symmetrical reversible low- density lesions in the internal and external capsules in eclampsia, a disease closely related to HE. The several studies indicate that reversible diffuse white matter hypodensity on CT scanning accompanies HE; its incidence awaits larger study.

The reversible diffuse white matter hypodensity observed on CT scanning is compatible with the presence of vasogenic cerebral edema, supporring the suggestion that cerebral edema accompanies HE in most cases. Severe acute hyper- tension is thought to disturb cerebral autoregulation, leading to vasodilatation and increased permeability of cerebral ar- terioles c 10). Despite the demonstration that cerebral edema accompanies HE, the cause of the mental status abnor- malities remains unclear. Widespread cerebral edema may be associated with cerebral tumor and infarction without accom- panying encephalopathic signs. The diffuse white matter edema we observed is secondary to transudation of fluid and protein across leaky arterioles. Many potential causes of mental status abnormalities could occur as a consequence of this breakdown of the blood-brain barrier. The reversible nature and location of the CT findings argue against the pathogenesis of HE being in most cakes secondary to infarc-

tion or to transient ischemia caused by small vessel occlusion or vasospasm [l, 2).

Departments of 'Neurology and f Radiology Worcester Memorial Hospital and University

Worcester, M A 01 605 of Massachusetts Medical School

~ ~~ ~~

We thank Dr Robert M. Black for referring the patient and Lynn C. Dalbeck for helping in the preparation of the manuscript.

References 1. Byron FB: The pathogenesis of hypertensive encephalopathy

and its relationship to the malignant phase of hypertension. Lancet 2:201-211, 1954

2. Chester EM, Agamanolis DP, Banker BQ, Victor M: Hypetten- sive encephalopathy: a clinicopathologic study of 20 cases. Neu- rology (NY) 28:928-939, 1978

3. Gaitz JP, Bamford C R Unusual computed tomographic scan in eclampsia. Arch Neurol 39:66, 1982

4. Healton EB, Brust JC, Feinfeld DA, Thomson GE: Hyperten- sive encephalopathy and the neurologic manifestations of malig- nant hypertension. Neurology (NY) 32:127-132, 1982

5. Jellinek EH, Painter M, Princas J, et al: Hypertensive encepha- lopathy with cortical disorders of vision. Q J Med 33:239-256, 1967

6. Kendall BE, Claveria LE, Quiroga W: CAT in leukodystrophy and neuronal degeneration. In Boulay GH, Moseley IF (eds): Computerized Axial Tomography in Medical Practice. New York, Springer Verlag, 1977

7. Klatzo I: Neuropathological aspects of brain edema. J Neuropathol Exp Neurol26:1-14, 1967

8. Plum F, Posner JB: The Diagnosis of Stupor and Coma, ed 3. Philadelphia, Davis, 1980, p 214

9. Rail DC, Perkins GD: Computerized tomographic appearance of hypertensive encephalopathy. Arch Neurol 37:3 10-3 I 1, 1980

10. Ram CVS: Hypertensive encephalopathy: recognition and man- agement. Arch Intern Med 138:1851-1853, 1978

11. Skinhoj E, Strandgaard S: Pathogenesis of hypertensive enceph- alopathy. Lancet 1:461-462, 1973

270 Annals of Neurology Vol 18 No 2 August 1985