What is the appropriate work‑up for a patient who developed left hand weakness after sleeping in an uncomfortable position for 90 minutes, with mild weakness of left wrist and finger extension and decreased sensation over the dorsal left thumb?

Radial Nerve Palsy ("Saturday Night Palsy") - Clinical Diagnosis Without Imaging

This presentation is classic for radial nerve compression neuropraxia (Saturday night palsy), and no imaging is required for initial management—this is a clinical diagnosis that typically resolves spontaneously with conservative treatment.

Clinical Reasoning

The clinical picture is pathognomonic for radial nerve injury:

• Weakness of wrist extension (extensor carpi radialis/ulnaris)
• Weakness of finger extension (extensor digitorum)
• Sensory loss over dorsal thumb (superficial radial nerve distribution)
• Mechanism: Prolonged compression during sleep in awkward position (90 minutes)

This constellation of findings localizes the lesion to the radial nerve in the spiral groove of the humerus, where it is most vulnerable to compression injury.

Immediate Management Steps

1. Complete Neurological Examination

Document the following specific deficits:

• Motor: Test wrist extension, finger MCP extension, thumb extension/abduction, brachioradialis strength
• Sensory: Map out exact distribution of numbness (first dorsal web space is classic)
• Reflexes: Check brachioradialis reflex
• Rule out: Posterior interosseous nerve syndrome (spares wrist extension, affects only finger/thumb extension)

2. Exclude Alternative Diagnoses

While the provided guidelines focus on trauma 1, this is not a traumatic injury requiring imaging. The key differentiators:

• No trauma history = no indication for radiographs
• No fracture suspected = imaging guidelines don't apply
• Compressive neuropathy = different diagnostic pathway

Critical pitfall: Don't order unnecessary imaging. A recent case report 2 describes isolated wrist drop from stroke, but this patient lacks vascular risk factors acutely and has a clear compressive mechanism.

3. Conservative Management Protocol

• Wrist cock-up splint in neutral position to prevent contracture
• Avoid further compression (no tight watches, arm positioning awareness)
• Physical therapy referral for passive range of motion
• Patient education: Expected recovery timeline is 6-12 weeks for neuropraxia

4. Electrodiagnostic Studies - Timing Matters

Do NOT order EMG/NCS immediately. Wait 3-4 weeks if:

• No clinical improvement by 2-3 weeks
• Progressive weakness develops
• Need to confirm diagnosis or assess severity

Electrodiagnostic studies are most informative after Wallerian degeneration is complete (3+ weeks), allowing differentiation between neuropraxia (good prognosis) versus axonotmesis (slower recovery).

When to Consider Advanced Imaging

MRI with neurography sequences 1 is indicated only if:

• Suspected mass lesion compressing nerve
• Concern for nerve transection (not applicable here)
• No improvement after 3 months
• Atypical features suggesting alternative diagnosis

The ACR guidelines 1 specifically address traumatic injuries and foreign bodies—none apply to this compressive neuropathy scenario.

Red Flags Requiring Urgent Evaluation

Immediately escalate if patient develops:

• Bilateral symptoms (consider central lesion/stroke) 2
• Proximal weakness (shoulder, elbow flexion)
• Other neurological signs (facial droop, speech changes, leg weakness)
• Severe pain out of proportion to examination
• Rapid progression over hours

Expected Prognosis

Most compression neuropraxias recover completely within 6-12 weeks with conservative management. Document baseline examination meticulously to track recovery objectively at 2-week intervals.

The absence of trauma, clear compressive mechanism, and classic radial nerve distribution make this a straightforward clinical diagnosis requiring reassurance, splinting, and watchful waiting—not imaging.