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MND – Medication Delivery — SCE Neurology MCQ

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HardPeripheral Neuropathy & NeuromuscularMND – Medication DeliverySCE Neurology

During ulnar motor studies, the below-elbow latency to ADM is 5.4 ms and the above-elbow latency is 7.9 ms. The measured across-elbow distance is 10 cm. Forearm conduction velocity is 58 m/s and there is no temperature artefact. What is the best interpretation?

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Reveal the answer and explanation

Correct answer: C — Across-elbow velocity is 40 m/s, supporting focal ulnar neuropathy at the elbow

Explanation lettering: E = shown as A · C = shown as B · D = shown as C · B = shown as D · A = shown as E

D is correct. Velocity equals distance divided by latency difference: 0.10 m / 0.0025 s = 40 m/s. This is below the usual 50 m/s across-elbow criterion and 18 m/s slower than the forearm, localising focal slowing to the elbow. A uses the latency difference as velocity and overcalls diffuse disease. B miscalculates. C discards the measured segment. E misses the conversion from milliseconds to seconds.

Reference: AANEM practice parameter for ulnar neuropathy at the elbow: https://www.aanem.org/docs/default-source/documents/aanem/practice/guidelines/practice-parameter-for-edx-studies-in-ulnar-neuropathy-at-the-elbow.pdf?sfvrsn=3de7ccad_1