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Neurophysiological diagnosis of polyneuropathies
Björn Falck, MD, PhDDepartment of clinical neurophysiologyUniversity hospitalUppsala, Sweden
Definition of polyneuropathy
Diffuse disorder of peripheral nervesOften all types of axons are involved
MotorSensoryAutonomic
Usually distal nerves more affected than proximalSymmetric
EtiologyToxic
Drugs, solvents….Metabolic ja endocrine
Diabetes, uremiaImmune mediated
AIDP, CIDP, MMN, MGUSHereditary
CMT, HNPPInfectious
Leprous, HIV, BorreliaMore than 300 different causes for PNP
Affected types of axonsSensory
PyridoxineMotor
LeadSensory and motor
MoOst PNPsDiabetes
Thin fibreFabry disease
Patophysiology
Axonal 80-90%Demyelinating 10-20%
Without conduction blockWith conduction block
Polyneuropathy - Site of primary defect
AxonopathiesCentral-peripheral axonopathyAxon transportCumulative effect of pathology along the nerve
NeuronopathiesPrimary events in the perikaryon
MyelinopathiesThe precise site and mechanism is not always known
Polyneuropathy – time course
Acute (days to weeks)Acute polyradiculitisCritical illnessPolyarteritis nodosaToxic polyneuropathiesPorphyria
Chronic (months to years)HMSNDiabetes
RelapsingChronic polyradiculitis
Distribution
Distal symmetricBy far most commonRelated to axon lengthLegs>arms
Proximal symmetricIntermittent porphyriaTangier diseaseSometimes polyradiculitis
DistributionUpper limb predominant
LeadDapsone
Complex distributionsLepromatous leprosy (skin temperature)
Cranial nerve involvementMiller-Fisher syndromeBorreliosisSarcoidosisSjögren’s syndrome
Polyneuropathy - Multifocal neuropathy
Multifocal mononeuropathies may superficially look like a polyneuropathyIn many polyneuropathies there is susceptibility for local neuropathies
DiabetesHereditary liability to pressure neuropathies
Epidemiology of PNP
2.4% of the population have PNP8 % of >65 year olds have PNPIn the western world diabetes most common In developing world leprous neuropathy is most common
Generation of symptoms
Loss of function (negative symptoms)Axonal lossConduction block
Abnormal excitablity (positive symptoms)HyperexcitabilityAbnormal spreadingn of impulsesAbnormal pathways
Polyneuropathy - motor symptoms
Loss of neural functionweakness
Increased abnormal neural functionfasciculationmyokymiamuscle cramps
Polyneuropathy - sensory symptoms
Loss of neural functiondecreased sensationtouchpaintemperature
Increased abnormal neural functionparesthesiadysesthesianeuropathic pain
Symptom chart Polyneuropathy - autonomic symptoms
Loss of neural functionHorner’s syndromeLoss of sweatingCardiovascular symptoms
Orthostatic hypotoniaGenitourinary function
Abnormal neural functioncardiovascular symptoms (vagal overactivity)
Polyneuropathy - clinical findings
Decreased tendon reflexesDecreased or altered sensation
VibrationPainTemperature
Loss of muscle strengthMuscle atrophyTrophic skin changes Joint deformities
Polyneuropathy - skeletal deformity
Pes cavusHMSNIndicates onset in childhood
Rarely pes planusScoliosisNeuropathic joint deformity
Pes cavus in CMT1aNeuropathic arthropathy
Lepromatous neuropathygreater auricular nervesupraclavicular nervesradial nerve at the wristetc
AmyloidosisCMT 1 and 2Neurofibromatosis
Polyneuropathy - nerve thickening Monofilament (10 g)
Monofilament test
Diagnosis of polyneuropathies
Daignosis and treatment of PNPDoes the patient have PNP?
PNP etiology?
Treatment
- Exposition, diseases- Symtoms- Clinical findins- ENMG
- Expostion,disprders- Clinical chemistry- Genetics- Other…..
- Is the underlying condition tratable?- Symptomatic treatment
Polyneuropathy - Neurophysiological criteria
The diagnosis is not always clearNormal aging causes alterations to the peripheral nerves
reduced CV with ageSCS amplitude reduced with age
How many abnormal findings are required for the diagnosis??Cumulative effects of lifestyle and aging
Methods availableHistoryClinical examinationNeurographyPsychophysiological methods
Vibration sensation thresholdsThermal sensation thresholds
EMGTests of the autonomic nervous systemIntraepidermal axon densityNerve biopsy
N. medianus
Normal median nerve neurography Axonal neuropathy
Axonal neuropathy
Reduced motor and sensory amplitudesConduction velocity normal or slightly reduced
median motor > 40 m/sDistal latency normal or slightly prolongedNo decay
Axonal PNP
Diabetic polyneuropathymay show features of demyelination
Hereditary motor and sensory polyneuropathy type 2 (HMSN 2)AmyloidosisRenal insufficiency
Conduction in abnormal nerves
Saltatory nerve conduction depends on the innermost myelin layersProlonged internodal conduction time from 20 us to 500 usConduction blocks arise due to local inexcitabilityNon-saltatory conduction requires reorganization of the axolemma
Demyelinating neuropathy
median nerve in a patient with HMSN 1
Demyelinating neuropathy
CV reduced >30% median nerve CV < 40 m/s
Distal latency > 7 msNormal or reduced amplitudes
Demyelinating and axonal neuropathy
Conduction block
median nerve, multifocal motor neuropathy with conduction blocks
Definition of conduction block
> 20% amplitude or area decay and less than 15% dispersion>50% amplitude or area decayBoth criteria are equally sensitive, but the latter is more specificAd hoc committee of the American Academy of Neurology AIDS taskforce, Neurology; 41: 617-618
Practical criteria of conduction block
Motor decay abnormal without dispersion
Upper extremities >25% decay and <15% dispersionLower extremities >40% decay and < 20% dispersion
Reduced number of F waves
Polyneuropathies with conduction block
Acute polyradicultis (AIDP)Chronic polyradiculitis (CIDP)Multifocal motor neuropathy with conduction blocks (MMN)DiphtheriaPolyneuropathies in gammopathies
Demyelinating no conduction block
Inherited polyneuropathiesCMT 1 Hereditary liability to pressure palsies
conduction blocks are limited to sites of local nerve lesions
Demyelinating with conduction block
Acquired demyelinating polyneuropathies show conduction blocks
Acute polyradiculitisChronic polyradiculitisDiphtheriaMMNPolyneuropathy associated with gammopathy
EMG
May be helpful in providing information about the involvement of alpha motor axonsDistributionTime course
Fibrillation potentialsMUP abnormalities
Differential diagnosisSpinal stnosis
Diabetic neuropathies
Classification of diabetes
Type 1 diabetesImmune, cell mediated destruction of β-cells 90%Idiopathic 10 %
Type 2 diabetesMultiple causesDefective insulin secretioninsulin resistance Genetic predisposition
Other specific typesGenetic defects of β-cell functionGenetic defects of insulin actionDiseases of exocrine pancreasEndocrinopathies
Gestational diabetes mellitusPrediabetes (Impaired glucose tolerance)
Epidemiology of DM
1.3% of population has DM27% DM type 173% DM type 2
Definition of diabetic neuropathy
“Diabetic neuropathy is is a descriptive term meaning a demonstrable disorder, either clinically evident or subclinical, that occurs in the setting of diabetes mellitus without other causes for peripheral neuropathy. The neuropathic disorder includes manifestations in the somatic and/or autonomic parts of the peripheral nervous system”
Report and Recommendations of the San Antonio Conference on Diabetic Neuropathy. Neurology 1988: 38; 1161-1165
Types of diabetic neuropathy
MononeuropathiesEntrapment neuropathiesAcute mononeuropathies (Parsonage-Turner syndrome)
Diabetic lumbosacral radiculoplexus neuropathy Bruns-Garland syndrome
Sensory-motor axonal polyneuropathyUsually high correlation between affection of different types of axonsThin fiber neuropathyAutonomic neuropathy
Acute painful diabetic neuropathyDiabetic neuropathic cachexia
Hyperglycemic polyneuropathyTransient neuropathy related to hyperglycemia, especially in patients with newly diagnosed diabetes
Definition of diabetic polyneuropathy
“…..confirmed definite clinical neuropathy also required the finding of unequivocal abnormality on nerve conduction studies or autonomic nervous system testing….”
Diabetes Control and Complication Trial Group. Effects of Intensive Diabetes Treatment on Nerve Conduction in the Diabetes Control and Complications Trial. Ann Neurol 1995; 38: 869-880
Staging of diabetic neuropathy
Stage 0No neuropathic symptoms< 2 abnormalities on neurophysiological tests
Stage 1 (Asymptomatic neuropathy)No neuropathic symptoms≥ 2 abnormalities on neurophysiological tests
Stage 2Neuropathic symptoms not disabling≥ 2 abnormalities on neurophysiological tests
Stage 3Neuropathic symptoms disabling≥ 2 abnormalities on neurophysiological tests
Dyck JD. Detection, characterization and staging of polyneuropathy; assesses in diabetics. Muscle Nerve 1988: 11; 21-32
Polyneuropathy in newly diagnosed diabetes
Patients are rarely investigated at this stageUsually no subjective symptomsReduced conduction velocitiesReversible within a few months
Predisposing factors
Duration of diabetesAgeGlycemic control as measured by GHbHeightOther diseases or exposure to toxins
AlcoholUremiaB12
Type of diabetes? Probably type2 > type1
Epidemiology of diabetic polyneuropathy
8% have polyneuropathy at the time of diagnosistype 2 > type 1
Overall 30% of diabetics have PNP> 20 years of diabetes 50% have PNP
type 1 > type 2
Pathology of diabetic polyneuropathy
Loss of myelinated and unmyelinated axons distallyLoss of anterior horn cells and sensory ganglion cells in some casesSegmental and paranodal demyelination (both primary and secondary)In patients with treated diabetes axonopathy predominates
Pathogenesis
Formation of glycosylation end productsAltered polyol metabolismAltered neurotrophic factorsOxidative stressAltered essential fatty acid metabolismVascular factors
Complications more severe in Type 1
PNP and retinopathy go hand in hand Diabetes not the only cause of PNP
Diabetes not the only cause of PNP
If diabetes patient with significant PNP does not have retinopathy look for other causes of PNP
Strategy in patients with diabetes
Assess polyneuropathySeverityPathophysiology (axonal-demyelinating)Distribution (distal-proximal, symmetry)Types of axons involved (sensory, motor, thin fibers, autonomic nervous system)
Assess local nerve lesionsCarpal tunnel syndrome in all patientsIf clinically symptoms other nerves
Neurography in diabetes
Superficial peroneal nerveSural nerveMedian nerveUlnar nerve
Peroneal nerveTibial nerveMedian nerve
Motor neurographySensory neurography
Depending on the clinical symptoms other nerves may be investigated
Sensitivity of different tests
% abnormal findings in 180 diabetes patients Nerve conduction (NC) 69 % Neuropathy symptom score (NSS) 54 % Neuropathy disability score (NDS) 48 % Neuropathy symptom score (NSC) 47 % Vibratory detection threshold (VDT) 44 % Cooling detection threshold (CDT) 35 %
Dyck JD et al. The sensitivity and specificity of vibratory and cooling thresholds
in the diagnosis of diabetic neuropathy. Diabetes Care 1987;10;432-440
Treatment
Hyperglycemic controlAldose reductase inhibitorsMyo-inositol administrationα-lipoic acidNeurotrophic factorsPancreatic transplantation
Controversial issues
Does prediabetes cause PNP?Do diabetic patients have an increased frequency of CIDP?
Prediabetes (Impaired glucose tolerance)
Fasting blood glucose 100-125 mg/dL2 hour glocose level after oral glucose test 140-199mg/dL.
Does prediabetes cause PNP?
Singleton et al (Diabetes care 2001) found in 107 patients with PNP of undetermined cause prediabetes in 34%
No control groupIn 30% of >65 year olds prediabetes
Hughes et al (Brain 2004) looked at similar PNP patients with a control group and found prediabetes equally common in both groups
CIDP in diabetes patients
Some reports indicate increased frequency of CIDP in diabetes patientsNot substanciated by epidemiologic studies (Muscle nerve 2006:34:512)
Further reading
CMT(Charcot-Marie-Tooth syndrome)Hereditary motor and sensory neuropathies
History
1886 Charcot J and Marie P (France)1886 Tooth H (UK)1893 Dejerine H and Sottas J 1926 Roussy G and Levy G
Jean-Martin Charcot 1867-1936
Pierre Marie 1853-1940 Howard Henry Tooth 1856-1925
DissertationUniversity of Cambridge”The peroneal type of muscle atrophy”1886
CMT
Hereditary sensory and motor polyneuropathies (PNP)Primary affection is PNPNo or little CNS symptomsFairly homogenous groupHundreds of different mutations affecting several different genes related with myelinMost are autosomal dominant (AD)A few are autosomal recessive Also x-linked forms exist
CMT terminology
CMTHSMN (hereditary sensory and motor polyneuropathy)
Introduced by Peter DyckCurrently less used
Usually in classifications CMT = HSMNCMT4 ≠ HMSN4HMSN3=Dejerine Sottas
Main clinical features
Onset in the first or second decade of lifeSymptoms mainly motorFoot deformity
Pes cavusDigitus malleus
Little subjective sensory abnormalitiesUnpleasant neuropathic symptoms rarePain due to deformity of the foot may cause pain
Slowly progressiveDo not reduced life expectancyRarely wheel chair bound
Pes cavus in CMT1a
Main clinical features Symptom onset in the first or second decadeSymptoms mainly motorFoot deformity
Pes cavusDigitus malleus
Little subjective sensory abnormalitiesUnpleasant neuropathic symptoms rarePain due to deformity of the foot may cause pain
Slowly progressiveDo not reduced life expectancyRarely wheelchair bound
CMT prevalence
All CMT 30/100000 CMT1 15/100000 CMT1A 10/100,000 CMT2 7/100,000
CMT classification
CMT1 (demyelinating)CMT2 (axonal)CMT DI (dominant intermediate)CMT 3 (severe early onset, demyelinating)CMT 4 HNPP (hereditary liability to pressure palsies)
Myelin proteinsExtracellular
Intracellular
PMP22 MAGConnexinP0
CMT1 – demyelinating, dominant
Gene Location OnsetCMT1A PMP22 17q11 1 decadeCMT1B P0 1q22 1 decadeCMT1C LITAF 16p13 2 decadeCMT1D EGR-2 10q21 2 decade
CMT1A
Most common CMT, 70% of all
AD, Linked to chromosome 17p11.2
Peripheral myelin protein 22 (PNP-22)
Duplication or point mutations
Genetic testing available
Male:female 1:1
Family history in 60%, 30% de novo mutations
Complete penetrance
Abnormal crossing over CMT1A variants
Roussy-LevyAtaxia and tremor
CMT1AReduced CV
<39 m/s in median nerveNote increased stimulation thresholdNo conduction blocks
Present from 2 years of ageDemyelination not detectable at birth
EMGIn young patients no signs of axonal involvementLater varying degrees of axonal degeneration
Axonal degeneration cause of handicap
CV in children with CMT1a
Garcia et al. CMT type 1a disease wit duplication 17a duplicaation in infancy and childhood. Neurology 1998;50:1061-
CMT1B
Autosomal dominant inheritance
Linked to chromosome 1q21-23
Peripheral myelin protein P0 (PNPO)
Gene mutations > 95
Sporadic cases common50%
1B is less common
CSF protein elevated
P0 protein
28kD219 amino acidsMost abundant peripheral nerve protein
50%Compact myelinNot present in CNSRequired for normal myelin function
CMT1C
LITAF –lipopolysaccaride-induced tumor necrosis factor-α
Stimulates monocytes and macrophagesMay play a role protein degradation
Autosomal dominantChromosome 16p13Three families describedSimilar to other CMT1
CMT1D
Zinc-finger transcription factor EGR2/Krox20Autosomal dominantOver expression of EGR2 leads increased expression of several myelin proteinsNeurophysiogically like other CMT1
CMT2 – axonal, dominant
CMT2A1 KIFB1β 10 yearsCMT2A2 Mitofusin 2 10 yearsCMT2B RAB 3q13 2 decadeCMT2C 12q23-q24 1 decadeCMT2D GARS 7p14 16-30 yearsCMT2E NF-68 8p21 1-40 yearsCMT2F HSPB1 7q11 2 decadeCMT2G 12q12 15-25CMT2H HSPB8 12q24 15-33
CMT2A1
Kinesin family number 1Bβ (KIF1B)Chromosome 1p36.2DominantDescribed in Japan
CMT2A2
Mitofusin 2 (MFN2)Autosomal dominantMost CMT2AMFN2 mitochondrial fusion protein
Outer membrane of mitochondriaRegulates OXPHOS expression
CMT2A2
CMT2A
Onset 1-52 yearsDistal weaknessSensory lossSometimes painfulIntention tremorHearing loss in 60%Wheelchair may be needed on 5th decade
CMT2A
CV>40 m/s in median nerveReduced amplitudes
EMG Axonal involvement
Dejerine-Sottas (HSMN3)
SevereInfantile onsetSlowlyAutosomal dominant
Most cases are sporadicFew become ambulatoryHypotonia, areflexiaPes cavus
CSF proteins elevated
Dejerine-Sottas (HSMN3)
Overlap with CMT1Is the eponym warranted?
Genetically heterogeneousPMP22P0Connexin-32
Dejerine-Sottas (HSMN3)
CV<10m/sNo sensory responses
EMG Signs of active denervation
CMTX
CMTX Connexin-32 Xq13 2 decade
CMTX
Connexin-32Chromosome Xq13Semidominant>240 point mutations
Phenotype depends on mutationConnexin function
Gap junctionUncompacted myelin
CMTX
MalesOnset < 20 yearsDistal weakness
FemalesAsymptomaticMay have slight slowing of CV
Family history
I. Autosomal dominant inheritanceC. Isolated cases
incomplete penetrancede novo mutations
I = Inclusion criterion
E = Exlusion criterion
C = Comment
Age at onset
I. Usually during second or third decadeC. Vide variability from birth to old age
Clinical manifestations
I. Acute recurrent peripheral nerve lesions, usually with good recoveryI. Acute deficits both sensory and motorI. Precipitating factors (trauma, pressure or stretching) usually identifiedI. Some mutation carriers remain asymptomaticC. Deficit may be purely sensory or motorC. Number of nerve lesions vary from one to manyE. Precence of pain before or during episodes
Location of nerve palsies
C. Peroneal nerve, ulnar nerve and brachial plexus often affectedC. Median and radial nerves may be affectedC. Other nerves, including cranial nerves may excptionally be affectedC. Several nerves may be simultaneously affected
Clinical findingsC. Tendon reflxes may be diminshed or abolished, ankle jerk most often affectedC. General areflexia may be notedC. Pes cavus may be presentC. Scoliosis may be presentC. Muscle weaknessa and wasting may be present in areas previous affectedC. Muscle weakness and wasting may be observed in ares not previously affectedE. Predominant CNS involvement incuding pyramidal tract or cerebellar signs
Course and severity
I. Absence of deficits between palsy episodesI. Complete recovery occurs within days to monthsC. Recovery may be incomlete
Neurophysiological criteriaI. Presence of diffuse neurography abnormalities in all mutation carriers, symptomatic or not, age >15 years
delayed median nerve MDL bilaterallyreduced median nerve CV palm to wristreduced CV or delayed DL in one peroneal nerve
C. Ulnar nerve CV often reduced at the elbowC. Motor CV reduced in lower limbsC. Sensory nerve action potentials reduced, especially in upper limbs
Molecular genetics
I. Deletion in 17p11.2 detected in 85-90% of HNPPI. Some point mutations in PMP22 cause HNPPE. Absence of HNPP deletionin 17p11.2 or point mutation
Prevalence
In south western Finland prevalence is at least 16/100 000 (Meretoja et al , Neuromusc Disord 1997;7:529-32)
Acute polyradiculitis
Acute polyradiculitisGuillain-Barré Syndrome, GBSAcute inflammatory demyelinating polyneuropathy, AIDP
Clinical featuresIn most patients distal and ascendingThe presentation may be descending in a portion of patientsPain in 15-50 % of patientsFacial nerve is often involvedAutonomic nervous system may be affected, especially in patients with severe motor deficitsTendon reflexes are decreased or absent
GBS – time courseMost patients worsen over 1-2 weeks, some for up to 4 weeks
Axonal reach quicker maximal weakness than demyelinating
After plateau subsequent recovery over 6-12 monthsPatients that worsen for more than 8 weeks probably have chronic polyradiculitis
GBS - StrategyDemonstrate acute motor and sensory neuropathyIn the acute stage the motor nerves are more affected than sensory nervesTypically demyelinating with conduction blockAxonal forms are also commonProximal demyelination and distal axonopathyMost prominent findings are often in the proximal parts of the nerves – sometimes the findings are distalSometimes the neuropathy is predominantly axonal, especially if associated with Campylobacter jejuniAssess: severity, pathology, distribution
GBS - Abnormal findings
MotorConduction blockF waves delayed and few DL prolongedReduced MCV, sometimes normal initiallyDistal amplitude may be initially normal - low amplitude with normal DL indicates severe axonal involvement
SensoryReduced SCV is not necessarily seen during the first weeksReduced amplitude is seen in the presence of axonal loss
GBS - Abnormal EMG findings
< 10-18 days from onset of symptoms: only reduced interference pattern> 10-18 days from onset: signs of acute neurogenic EMG findings
GBS - ProcedureNeurography
MCS: n.medianus, n.ulnaris, n.tibialis, n.peroneus unilaterallySCS: n.radialis, n.suralis unilaterally.
EMG< 10 days from onset of symptoms not necessarily informative, but may reveal earlier onset and confirm peripheral cause of weakness > 10 days from onset,
Autonomic tests (optional)RR-intervalSSR
Sensory thresholds (optional)temperaturevibration
Chronic polyradiculitis (Chronic inflammatory demyelinating polyneuropathy, CIDP)
CIDP - CourseOccurs in all age groups from 2 yearsMay begin as a typical acute polyradiculitisMay start with subacute symptomsCourse
chronic progressive (slowly or stepwise) courserelapsing
progression > 6 weeks followed by episodes of improvement and worsening for at least 3 months
CIDP - Symptoms
Bilateral relatively symmetric weakness - distal and proximalParesthesias in toes and fingersFacial muscles may be affected (10-15% of patients)
CIDP - Prognosis
Patients with a relapsing course often resolve after a few years and they tend to have a better prognosis than those with chronic progressive course
CIDP - Other investigations
Elevated CSF protein concentration during deteriorationMRI shows increased signals on T2 weighted images at the sites of conduction blocksNerve biopsy not useful
CIDP - Abnormal neurography findings
Motor neurographyReduced CVConduction blockF waves delayed and fewDistal latency prolongedDistal ampl may be initially normal - low amplitude with normal dist.lat. indicates severe axonal involvement
Sensory neurographyReduced SCV Reduced amplitude
CIDP Abnormal EMG findings
Distal muscles and proximal muscles show neurogenic findingsDepends on severity
CIDP - Abnormal findings
Autonomic nervous system testsRR-interval often abnormalSSR may be abnormal
CIDP - ProcedureNeurography
Motor: n.medianus, n.ulnaris, n.tibialis, n.peroneus unilaterallySensory: n.radialis, n.suralis unilaterally.
EMG one proximal and distal muscle in the upper and lower extremities
Autonomic tests (optional)Sensory thresholds (optional)
Miller-Fisher syndrome
Miller- Fisher M. An unusual variant of acute idiopathic polyneuropathy (syndrome of ophthalmoplegia, ataxia and areflexia) N Eng J Med 1956;255:57-60
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Miller-Fisher syndrome - Clinical features
External ophthalmoplegia, ataxia and areflexiaDiplopia and unsteadiness of gait, either of these symptoms may be the initial signOther muscles innervated by cranial nerves may show weakness
Miller-Fisher syndrome - Clinical
Acute onset within daysPeak of symptoms in one to two weeksMild weakness and sensory symptoms may be presentUsually the course is monophasic and relatively benignRecurrences have been describedCSF protein is elevatedAntibodies against GQ1b
Miller-Fisher syndrome - Neurography
MotorF waves delayed and few due to conduction blockDL may be prolongedMildly reduced MCV, sometimes normal initiallyDistal amplitude reduced, especially in facial muscles
SensoryReduced amplitude dominates over reduced CV
Miller-Fisher syndrome - Blink reflex
Absent or mildly prolonged R1 componentsR2 may be absent, but latency is usually normal
Miller-Fisher syndrome
NeurographyMotor: n.medianus, n.ulnaris, n.tibialis, n.peroneusunilaterally, the branches of n.facialis bilaterallySensory: n.radialis, n.suralis unilaterally
EMG> 10 days from onsetFacial muscles should be studied
Blink reflexAutonomic tests (optional)
RR-intervalSSR
Sensory thresholds (optional)temperature and vibration
Utility of neurophysiological tests in the diagnosis of PNP
Role of neurophysiological tests
Diagnose PNP Characterize PNP
Axsonal-demyelinating-conduction blocksMotor-sensory-autonomicMyelinated-unmyelinated axonsSeverity
PrognosisSmall M wave amplityde in the acute stage may be related with a poor recovery
Follow-up
Timing of electrodiagnosis
In acute PNP ENMG immediately!!!Neurography shows abnormalities early Needle EMG shows abnormalities after 2-3 weeksIn the early stages it is not possible to distinguish between distal conduction block and axonal damage (pseudo block)
CharacterizationPathophysiology
AxonalDemyelinating (with or witout conduction blocks)
SeverityMildModerateSevere
DistributionDistal>proximalProximal > distalProximal=distal
Time courseAcuteChronic
Examples of characterization
Mild, chronic, symmetric, distal sensory-motor axonal polyneuropathyModerate, acute, demyelinating, distal sensory-motor-autonomic polyneuropathy with conduction blocks
Strengths
Guides the diagnostic etiological evaluationObjective and reliable in the diagnosis of symmetric sensory motor polyneuropathyQuantitativeSensitiveMost methods are non-invasiveCost is relatively low
Weaknesses
Routine methods do not measure function of thin myelinated and unmyelinated axonsVariability of repeated measurements for some of the methods is relatively highRoutine methods measure only loss of neural function
Diagnostic difficultiesAging
Normal aging causes mild neuropathic changes Mononeuritis multiplexFalse positive diagnosis
Spinal stenosis in older subjectsDistal myophyALS
False negative diagnosisMild sensory neuropathiesThin fibre neuropathy