1/22/2019. Nerve conduction studies. Learning objectives: Jeffrey Allen MD University of Minnesota Minneapolis, MN

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1 Jeffrey Allen MD University of Minnesota Minneapolis, MN February 9, 2019 Learning objectives: Describe electrophysiologic features of peripheral nerve demyelination Identify electrophysiology findings in acquired demyelination and genetically determined demyelination Identify common errors that are made during the interpretation of demyelinating electrophysiologic studies Nerve conduction studies Learning A brief introduction objectives: Describe electrophysiologic features of peripheral nerve demyelination Identify electrophysiology findings in acquired demyelination and genetically determined demyelination Identify common errors that are made during the interpretation of demyelinating electrophysiologic studies 1

2 Nerve conduction studies A brief introduction Nerve conduction studies A brief introduction Number of muscle fibers that fire Number of muscle fibers that fire Synchronicity of firing Synchronicity of firing Velocity of fastest conduction fibers + time to cross NMJ + muscle depolarization Velocity of fastest conduction fibers + time to cross NMJ + muscle depolarization Conduction Velocity = Distance/Time Conduction Velocity = Distance/Time 2

3 Axon loss Small responses Demyelination Slow responses Axon loss Small responses Electrophysiologic slowing manifests as: Conduction Demyelination velocity slowing Distal Slow latency responses prolongation Demyelination Temporal Slow Dispersion responses Duration increase >30% Area stable Electrophysiologic slowing manifests as: 3

4 Conduction Temporal Dispersion Block Amplitude Duration increase drop > 50% >30% Duration Area stable increase 30% Area reduced > 50% Conduction Block Amplitude drop > 50% Duration increase 30% Area reduced > 50% Electrodiagnostic criteria for CIDP according to EFNS/PNS criteria (2010) Definite: at least one of the following Motor distal latency prolongation 50% ULN in two nerves Reduction of motor conduction velocity 30% below LLN in two nerves Prolongation of F-wave latency 30% above ULN in two nerves Absence of F-waves in two nerves if these nerves have distal CMAP amplitudes 20% of LLN + 1 other demyelinating parameter Partial motor conduction block: 50% amplitude reduction in two nerves Abnormal temporal dispersion (>30% duration increase) Distal CMAP duration increase in 1 nerve (specific cut offs provided in criteria) + one or more parameter in other nerve Probable Partial motor conduction block: 30% amplitude reduction in two nerves, or in one nerve + 1 other demyelinating parameter Possible As in definite but in only one nerve 4

5 Electrodiagnostic Differential diagnosis criteria for of CIDP according Demyelinating to EFNS/PNS polyneuropathies criteria (2010) Definite: at least one of the following Motor Immune distal latency mediated prolongation 50% ULN in two nerves Reduction GBS of motor (AIDP) conduction velocity 30% below LLN in two nerves Prolongation CIDP of F-wave latency 30% above ULN in two nerves MMN Absence of F-waves in two nerves if these nerves have distal CMAP amplitudes Anti-MAG 20% of polyneuropathy LLN + 1 other demyelinating parameter POEMS Partial motor conduction block: 50% amplitude reduction in two Toxic nerves(diphtheria, others) Abnormal Medications temporal dispersion (tacrolimus, (>30% duration TNFα increase) Distal CMAP duration increase in 1 nerve (specific cut offs provided antagonists in criteria), + others) one or more parameter in other nerve Probable Genetically determined Partial motor conduction block: 30% amplitude reduction in two nerves, Charcot-Marie-Toot or in one nerve + 1 other demyelinating type I parameter HNPP Possible As in definite Others but in only (Farbers, one nerve Refsum, mitochondrial, others) Differential diagnosis of Demyelinating polyneuropathies Immune mediated GBS (AIDP) CIDP MMN Anti-MAG polyneuropathy POEMS Toxic (diphtheria, others) Medications (tacrolimus, TNFα antagonists, others) Genetically determined Charcot-Marie-Toot type I HNPP Others (Farbers, Refsum, mitochondrial, others) Differential diagnosis of Demyelinating polyneuropathies Immune mediated GBS (AIDP) CIDP MMN Anti-MAG polyneuropathy POEMS Toxic (diphtheria, others) Medications (tacrolimus, TNFα antagonists, others) Genetically determined Charcot-Marie-Toot type I HNPP Others (Farbers, Refsum, mitochondrial, others) Suspect acquired immune neuropathy: Variable degree of CV slowing often with CB or TD Suspect hereditary neuropathy: Uniform CV slowing typically without CB or TD Evidence Differential of diagnosis peripheral of Demyelinating polyneuropathies Immune mediated GBS (AIDP) Distal CIDPlatency prolongation Prolonged MMN CMAP duration Anti-MAG polyneuropathy POEMS Suspect acquired immune neuropathy: Variable degree of CV slowing often with CB or TD Accurately determining demyelinating parameters is critically important Genetically determined Charcot-Marie-Toot type I Suspect hereditary neuropathy: Uniform CV slowing typically without CB or TD 5

6 Technical pitfalls: Suspect acquired immune neuropathy: Adequate Variable degree temperature of CV slowing often Markers with CB or TD are correctly placed Stimulation supramaximal No Accurately co-stimulation determining demyelinating parameters is critically important Technical pitfalls: Adequate temperature Markers are correctly placed Stimulation supramaximal No co-stimulation Suspect hereditary neuropathy: Uniform CV slowing typically without CB or TD Common Interpretive Errors: 1. Amplitude dependent slowing in length-dependent polyneuropathies or ALS 2. Amplitude independent slowing in diabetic patients 3. Slowing is limited to compressible sites 4. Fibular nerve to EDB muscle is the primary diagnostic abnormality Interpretive pitfalls: Demyelinating abnormalities should be unequivocal Technical pitfalls: Adequate temperature Markers are correctly placed Stimulation supramaximal No co-stimulation Published guidelines can help! Technical pitfalls: Conclusions: Interpretive pitfalls: 1. Adequate Electrophysiologic temperature features of demyelination Demyelinating abnormalities Markers Conduction are correctly velocity slowing placed should be unequivocal Stimulation Distal latency supramaximal prolongation No co-stimulation 2. Common Acquired Interpretive vs Genetically Errors: determined demyelination 1. Amplitude Acquired: dependent Variable slowing degree in of CV slowing often with CB or TD length-dependent Genetic: Uniform polyneuropathies CV slowing or without CB or TD ALS Amplitude Electrophysiologic independent slowing pitfalls in diabetic Technical: patients Ensure adequate temperature, Published marker placement, guidelines 3. Slowing stimulation is limited to compressible sites 4. Fibular Interpretive: nerve to EDB Ensure muscle that is the the demyelinating can changes help! can not be easily primary explained diagnostic by abnormality something else 6

7 Conclusions: 1. Electrophysiologic features of demyelination Thank you 2. Acquired vs Genetically determined demyelination Acquired: Variable degree of CV slowing often with CB or TD Genetic: Uniform CV slowing without CB or TD 3. Electrophysiologic pitfalls Technical: Ensure adequate temperature, marker placement, stimulation Interpretive: Ensure that the demyelinating changes can not be easily explained by something else Published guidelines can help! 7