| Table 12. Electrodiagnostic Studies: Terminology | |
| Parameter | Definition |
| Amplitude | In motor-conduction studies: height in millivolts of CMAP from baseline to peak, i.e., number of muscle fibers activated by stimulus at a particular site In sensory-conduction studies: height in microvolts of SNAP from baseline to peak |
| CMAP | Summation of all muscle-fiber action potentials activated by motor nerve stimulation |
| Conduction velocity | Speed in meters per second of nerve impulse conduction |
| F wave | Assesses conduction along the proximal portion of the motor nerve; most commonly used in evaluating demyelinating neuropathies |
| Firing pattern | The number, size, and shape of motor units that initially fire and then recruit other motor units to fire, following voluntary muscle contraction |
| H reflex | Analogous to the ankle-jerk reflex but reflex is stimulated by a submaximal electrical current that selectively activates IA afferent sensory fibers (to cause a motor reflex) |
| Latency | In motor-conduction studies: time in milliseconds for conduction of a stimulus along the length of the nerve, transmission of the neurotransmitter-mediated signal across the neuromuscular junction, and depolarization of the muscle-fiber membrane In sensory-conduction studies: conduction time of the fastest-conducting fibers along a given segment |
| SNAP | Summation of individual action potentials of all the fibers activated |
| Spontaneous activity | Measures endplate muscle activity when a needle is placed near the neuromuscular junction (including spontaneous discharges - i.e., fibrillations and fasciculations - of muscle activity at rest) |
| CMAP, compound muscle action potential; SNAP, sensory nerve action potential. | |
| Based on Raynor [3], Lynn and Mendell [11]. | |
| Table 13. Electrophysiologic Findings of Axonal vs. Demyelinating Peripheral Neuropathies | ||
| Study | Axonal degeneration | Segmental demyelination |
| Motor-nerve conduction studies | ||
| CMAPa amplitude | Decreased | Normalb |
| Distal latency | Normal | Prolonged |
| Conduction velocity | Normal | Slow |
| Conduction block | Absent | Present |
| Temporal dispersion | Absent | Present |
| F wave | Normal | Prolonged or absent |
| H reflex | Normal | Prolonged or absent |
| Sensory-nerve conduction studies | ||
| SNAP amplitude Distal latency Conduction velocity |
Decreased Normal Normal |
Normal Prolonged Slow |
| Fibrillations | Present | Absent |
| Fasciculations | Present | Absent |
| Recruitment | ||
| Number of motor units | Decreased | Decreased |
|
a Compound motor action potential. b Except with conduction block. | ||
| Reprinted with permission from Barohn R: Approach to peripheral neuropathy and neuronopathy. Semin Neurol. 1998;18(1):7-18. | ||
| Table 14. Categorical Classification of Selected Peripheral Neuropathies | |
| Axonal | Demyelinating |
| Mononeuropathies | |
| Diabetes | Entrapments |
| Generalized neuropathies | |
| Diabetes Alcohol Carcinoma Vitamin deficiencies Toxic/metabolic neuropathies [Table 6], including heavy metals, industrial solvents and hydrocarbons, and medications Hereditary peroneal muscular atrophy Familial amyloidosis Porphyria Whipples disease Leprosy |
Guillain-Barre syndrome Leprosy Hereditary peroneal muscular atrophy/Dejerine-Sottas disease Diphtheria Chronic inflammatory demyelinating polyneuropathy (CIDP) Toxic neuropathies |
| Table 16. Management of Neuropathic Pain | |
| Symptom | Treatment |
| Mild neuropathic pain | Simple non-narcotic analgesics such as nonsteroidal anti-inflammatory agents or tramadol hydrochloride up to 50 mg PO t.i.d. may be helpful for all types of pain |
| Diffuse, poorly localized pain | Amitriptyline, 10-150 mg/day, in gradually increasing dosages (contraindicated in heart block, urinary tract obstruction, or narrow-angle glaucoma) If orthostatic hypotension is problematic: Other tricyclic depressants, including nortriptyline |
| Sharp, well-localized pain | Carbamazepine: initial dose, 100 mg b.i.d.; gradually increasing to 400-1,200 mg/day as tolerated If carbamazepine is not tolerated: Phenytoin, in gradually increasing doses beginning with 300 mg/day Gabapentin, beginning with 100-300 mg/day and titrating up to 600 mg t.i.d. or more Capsaicin, 0.075% topical ointment, applied q.i.d. For both diffuse and sharp pains: Mexiletine, up to 10 mg/kg/day |
| Lancinating pains | Clonazepam, 0.5-10.0 mg/day |
| Nocturnal leg pain, cramping | Clonidine, 0.1-0.5 mg q.h.s., quinine sulfate 200-400mg at bedtime |
| b.i.d., twice daily; q.h.s., before bedtime; q.i.d., 4 times a day; PO, orally; t.i.d., 3 times a day. | |
| Modified from Lynn and Mendell [11]. | |
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