CASE PRACTICE
32 original case and concept questions. Read the explanation after each answer and revisit the relevant chapter.
Choose one best answer. Practice history is stored only in this browser.
Stimulation sites are 240 mm apart. Distal onset latency is 3.2 ms and proximal onset latency is 8.0 ms. What is the segmental motor velocity?
Answer: 50 m/s
240 ÷ (8.0 − 3.2) = 50 m/s. Use the latency difference; mm/ms already has the numerical value of m/s.
Review the related chapterWhich latencies are compared when calculating motor conduction velocity between two stimulation sites?
Answer: CMAP onset latencies
Segmental motor velocity uses proximal minus distal CMAP onset latency, removing the shared distal pathway time. Peak position is also influenced by dispersion.
Review the related chapterHand skin temperature is 28°C and several sensory latencies are prolonged. What is the best next step?
Answer: Warm the limb, document temperature and repeat measurements
Cold may prolong latency and slow velocity. Restore method-matched acquisition conditions before distinguishing technical effects from disease.
Review the related chapterRadial digits become numb at night. After warming, matched same-hand comparisons show relative median slowing. Which site is best supported?
Answer: Median nerve at the wrist
Focal median delay relative to neighboring nerves supports wrist localization. The AIN has no cutaneous supply. Clinical findings and the remaining study must still agree.
Review the related chapterThumb IP and index DIP flexion are weak without cutaneous sensory loss. Which branch best fits?
Answer: Anterior interosseous
FPL and index FDP are AIN muscles, and the AIN has no skin territory. Assess PQ and consider tendon injury or a more proximal fascicular lesion.
Review the related chapterHand intrinsic weakness and ulnar palmar numbness occur with a preserved DUC response. Which site deserves particular assessment?
Answer: Guyon canal
DUC leaves proximal to the wrist and is commonly spared in Guyon canal disease. This is not diagnostic alone; assess the across-elbow segment and other muscles.
Review the related chapterFinger extension is weak, wrist extension is preserved with radial deviation, and radial dorsal hand sensation is normal. Which branch best fits?
Answer: PIN
The PIN supplies most finger extensors and has no cutaneous supply. ECRL branches more proximally, allowing wrist extension with radial deviation. Compare proximal radial and C7–C8 muscles.
Review the related chapterTo distinguish common fibular neuropathy from an L5 root lesion, which muscle gives L5 information outside the common fibular nerve?
Answer: Tibialis posterior
Tibialis posterior has tibial supply and L5 contribution. EDB, TA and EHL are deep fibular muscles. TP and TFL add cross-nerve information.
Review the related chapterWhich muscle helps distinguish a sciatic fibular-division lesion from a fibular-head lesion?
Answer: Biceps femoris, short head
The short head of biceps femoris receives fibular-division supply above the knee. Abnormality adds proximal information but still needs comparison with other muscles and root hypotheses.
Review the related chapterKnee extension is weak and the knee reflex is reduced, while hip adduction is preserved. Which mononeuropathy best fits?
Answer: Femoral
Quadriceps has femoral supply; hip adduction is mainly obturator. Saphenous SNAPs, adductors and paraspinals help compare lumbar plexus and L2–L4 lesions.
Review the related chapterAnterolateral thigh burning and numbness occur with normal strength and knee reflexes. Which nerve best matches?
Answer: Lateral femoral cutaneous
The LFCN is sensory, and its dysfunction may cause meralgia paresthetica. Weakness or reflex abnormalities require a broader localization.
Review the related chapterWhy are distal SNAPs often preserved in a typical preganglionic root lesion?
Answer: The lesion is usually proximal to the dorsal root ganglion
Distal sensory axons and their ganglion cell bodies are relatively preserved in typical preganglionic disease. Exceptions and coexisting conditions prevent this clue from being diagnostic alone.
Review the related chapterCorresponding SNAPs are reduced and abnormal muscles span terminal nerves within a plexus distribution. Which pattern is more plausible?
Answer: A postganglionic plexus lesion
Plexus disease may affect both corresponding SNAPs and muscles across terminal nerves. Exclude generalized neuropathy, multiple local nerve injuries and mixed root/plexus disease.
Review the related chapterOnly one paraspinal site has spontaneous activity; sampled limb muscles are normal. What is the most appropriate interpretation?
Answer: Consider nonspecific changes and sampling limitations
Isolated paraspinal abnormalities can be influenced by age or prior surgery. Interpret with limb findings and the clinical picture rather than assigning a precise root or disease alone.
Review the related chapterWhat is the best interpretation of fibrillation potentials and positive sharp waves?
Answer: Muscle-fiber membrane instability; assess distribution and cause
They occur with denervation and some myopathies, and are not specific to one disease or an exact injury date.
Review the related chapterFasciculations are observed without progressive weakness or other neurogenic evidence. What should you conclude?
Answer: Clinical integration is needed; this alone does not diagnose ALS
Fasciculation is a discharge phenomenon occurring in benign and pathological settings. ALS assessment requires progression, distribution, neuronal evidence and exclusion of alternatives.
Review the related chapterMany short, small MUAPs appear with slight effort. Which pattern is most consistent?
Answer: Myopathic early recruitment
When each unit contains fewer effective fibers, more units are recruited for the same force. Interpret morphology with recruitment; severe or chronic myopathy may look mixed.
Review the related chapterA patient is in pain, with a few units firing slowly and inconsistently. What should you consider first?
Answer: Poor activation and participation limits
Poor activation differs from true reduced recruitment. Document pain and effort limitations rather than overcalling motor-unit loss.
Review the related chapterA distal CMAP is still present one day after trauma. Does this exclude axonal injury?
Answer: No; distal degeneration takes time
Distal responses can persist before degeneration. Recruitment and other observations may still be useful. Decide follow-up from the clinical question rather than overinterpreting an early study.
Review the related chapterThe proximal CMAP has lower amplitude and longer duration. What is the best next step?
Answer: Check stimulation, area, dispersion and applicable criteria
Dispersion and phase cancellation may reduce amplitude; inadequate stimulation is also common. Assess the whole waveform and disease-specific criteria before supporting block.
Review the related chapterUlnar proximal/distal CMAPs differ atypically, and median stimulation also activates the relevant hand muscle. What should you consider?
Answer: Martin–Gruber communication
Forearm median-to-ulnar motor communication can alter CMAP distribution. Confirm systematically with consistent recording rather than diagnosing block from amplitude loss alone.
Review the related chapterWhich best describes an F wave?
Answer: A late response from backfiring of some motor neurons
F waves arise from backfiring of a subset of motor neurons after stimulation. H reflexes include Ia input. An F-wave abnormality alone cannot precisely identify a root.
Review the related chapterThe first RNS response is 10 mV and the fourth is 8.5 mV. What is the decline relative to the first?
Answer: 15%
(10 − 8.5) ÷ 10 × 100 = 15%. The baseline is the denominator. Clinical meaning also requires reproducibility, technique and appropriate limits.
Review the related chapterIs increased jitter found only in myasthenia gravis?
Answer: No; reinnervation and other conditions may increase it
Jitter is sensitive to transmission abnormality but is not specific to one cause. Interpret alongside routine EMG and clinical context.
Review the related chapterBurning feet and altered pain/temperature sensation occur with normal routine NCS. Which statement is correct?
Answer: Small-fiber disease and other causes remain possible
Routine NCS predominantly tests larger myelinated fibers. It does not exclude small-fiber disease, but symptoms plus normal NCS do not automatically establish that diagnosis either.
Review the related chapterOne common compression segment is mildly slow and other evidence is insufficient. Can this diagnose CIDP?
Answer: No; the full clinical and multinerve criteria are needed
CIDP requires time course, phenotype and the complete electrophysiological framework. Exclude cold, entrapment, very low CMAPs and other confounders.
Review the related chapterRapid limb weakness and swallowing difficulty occur with nondiagnostic early NCS. What matters most?
Answer: Continue urgent clinical assessment; early testing cannot exclude GBS
Respiratory, bulbar and autonomic risks need immediate assessment. Early EDX may be atypical and must not delay necessary care.
Review the related chapterRepetitive single-muscle-fiber activity waxes and wanes in frequency and amplitude. Which pattern fits?
Answer: Myotonic discharge
Myotonic discharges commonly wax and wane. Distinguish them from fixed repetitive CRDs and motor-unit-origin neuromyotonic discharges.
Review the related chapterHow should a learner respond when a person scheduled for testing takes anticoagulants?
Answer: Have the appropriate clinical team assess risk and the study plan
Bleeding and thrombotic risks must be balanced by the clinical team. A learning website cannot replace individualized medication or deep-muscle sampling decisions.
Review the related chapterCan a plantar mixed-nerve amplitude limit be applied directly to another pure sensory technique?
Answer: No; match the stimulation, recording and parameter definitions
Distance, recording method and amplitude definition determine whether reference data apply. Different techniques cannot be interchanged directly.
Review the related chapterWhat are the main input and output nerves of the conventional blink reflex?
Answer: V1 input, VII output
The blink reflex integrates ophthalmic trigeminal input, brainstem circuits and facial output. The pupillary reflex is a different circuit.
Review the related chapterOnly routine large-fiber NCS was performed, without needle EMG. Which conclusion is appropriate?
Answer: Describe the tested responses and state the needle and small-fiber limitations
Conclusions must match the scope of testing. Without needle or specialized small-fiber assessment, a report cannot claim a complete exclusion of those conditions.
Review the related chapter