Abstract
distal latency with preserved distal amplitude and mild partial sensory conduction block at the wrist. 2. Right median thenar CMAP was reduced in amplitude with initial positive deflection; normal amplitude was restored with stimulation over the ulnar nerve. Median CMAP at lumbrical II was mildly delayed with borderline decreased amplitude. 3. Needle EMG examination of the right APB was normal. Impression: 1. Mild to moderate right median neuropathy at the wrist (carpal tunnel syndrome). 2. Right Riche-Cannieu anastomosis. Discussion: Riche-Cannieu anastomosis is a common neuroanatomical variant involving a deep ulnar motor-to-recurrent median branch anastomosis. The “all ulnar hand“ may initially appear on nerve conduction studies to resemble a severe median neuropathy. This misdiagnosis may lead to unnecessary surgical intervention. Conclusions: Riche-Cannieu anastomosis should be included in the differential when median thenar CMAP is severely reduced in the setting of well-preserved thenar musculature.
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