Diagnosis: Ulnar Neuropathy at the Wrist (Distal Ulnar Nerve Lesion)
This patient has an isolated lesion of the superficial sensory branch of the ulnar nerve at the wrist level, most likely from perioperative positioning or compression during surgery.
Key Diagnostic Features
The nerve conduction study pattern is pathognomonic for a distal ulnar nerve lesion:
- Reduced right ulnar sensory amplitude with normal motor studies indicates selective injury to the superficial sensory branch of the ulnar nerve, which branches at the wrist level 1
- Normal medial antebrachial cutaneous nerve excludes more proximal lesions at the elbow or above, as this nerve would be affected by cubital tunnel syndrome 1
- Normal dorsal ulnar cutaneous nerve is the critical finding that localizes the lesion to the wrist rather than the elbow, since the dorsal ulnar cutaneous nerve branches 5-8 cm proximal to the wrist and would be spared in wrist-level compression 1
- Absence of motor weakness with normal motor nerve conduction studies excludes deep motor branch involvement and confirms this is purely a superficial sensory branch injury 1, 2
Mechanism: Perioperative Positioning Injury
This presentation is consistent with perioperative peripheral neuropathy from surgical positioning:
- Ulnar neuropathy at the wrist can occur from direct pressure on the hypothenar eminence or ulnar aspect of the hand during surgery, particularly if the hand was positioned against hard surfaces or improperly padded 3
- The American Society of Anesthesiologists guidelines emphasize that pressure points must be adequately padded to prevent peripheral nerve injuries, and ulnar nerve injuries can occur from multiple positioning scenarios 3
- Onset upon awakening from surgery with symptoms present immediately postoperatively is classic timing for positioning-related nerve injury 3
Differential Diagnosis Excluded
- Cubital tunnel syndrome is ruled out by normal dorsal ulnar cutaneous nerve studies, as this nerve branches proximal to the elbow and would be affected in elbow-level compression 1
- Guyon's canal syndrome (compression of the deep motor branch) is excluded by absence of motor weakness and normal motor conduction studies 1
- Cervical radiculopathy is excluded by the isolated ulnar sensory distribution without motor involvement and normal medial antebrachial cutaneous nerve 4
Prognosis and Management
- Conservative management is appropriate with observation, as most perioperative positioning injuries show spontaneous recovery over weeks to months 3, 1
- Electrodiagnostic studies should be repeated if symptoms worsen or fail to improve, to assess for progression from demyelinating to axonal injury 1
- Paracetamol up to 4g daily should be used as first-line analgesia if needed, with topical NSAIDs for localized discomfort 1
- Surgical exploration is not indicated at this early stage (one week post-onset) given the purely sensory nature, absence of motor involvement, and typical perioperative etiology 1, 2