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Ulnar Neuropathy at Guyon Canal — SCE Neurology MCQ

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ModeratePeripheral Neuropathy & NeuromuscularUlnar Neuropathy at Guyon CanalSCE Neurology

A 55-year-old man presents with progressive weakness of the right hand grip over 3 months. He has wasting of the first dorsal interosseous and hypothenar muscles. He also has sensory loss affecting the medial 1.5 fingers and the medial palm. NCS show reduced ulnar SNAP and CMAP amplitudes with normal median nerve studies. The lesion is at the wrist. What structure is compressed?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: E — Guyon canal (ulnar tunnel at the wrist)

Ulnar neuropathy at the wrist occurs at Guyon canal, between the pisiform and hook of hamate. It can affect motor fibres (deep branch — hand intrinsic weakness without sensory loss), sensory fibres (superficial branch — medial 1.5 finger numbness without weakness), or both. This patient has both motor and sensory involvement suggesting proximal Guyon canal compression. Causes include ganglion cysts, fractures (hook of hamate — common in cyclists and racquet sport players), and repetitive trauma. A: Carpal tunnel affects median nerve. C: Cubital tunnel is at the elbow. D: TOS has different features. E: C8 root affects multiple nerves.

Reference: AANEM Ulnar Neuropathy Guidelines; Preston & Shapiro