Does Saturday night radiculopathy affect the ulnar or radial nerve?

Saturday Night Palsy Affects the Radial Nerve, Not the Ulnar Nerve

Saturday night palsy exclusively affects the radial nerve, causing characteristic wrist drop and finger extension weakness due to compression of the radial nerve against the spiral groove of the humerus. 1, 2, 3

Clinical Presentation and Pathophysiology

Saturday night palsy (also called "Saturday night radiculopathy" in your question) is actually a misnomer - it is a peripheral neuropathy, not a radiculopathy. The condition occurs when the radial nerve is compressed against the spiral groove of the humerus, typically during deep sleep with the arm draped over a firm object, often after alcohol consumption. 1, 3

The clinical presentation includes:

• Wrist drop (inability to extend the wrist)
• Inability to extend the fingers and thumb
• Sensory changes on the dorsum of the first to third fingers
• Preserved ability to flex the wrist and fingers (ulnar and median nerve functions)

Anatomical Considerations

The radial nerve is particularly vulnerable to compression because:

• It travels through the spiral groove of the humerus
• It has a relatively superficial course at the lateral aspect of the arm
• It lacks significant surrounding protective tissue in certain areas

The ulnar nerve, by contrast, is not typically affected in Saturday night palsy. Ulnar nerve compression more commonly occurs at the elbow (cubital tunnel) or wrist (Guyon's canal), presenting with different symptoms including:

• Weakness of finger abduction/adduction
• Clawing of the 4th and 5th digits
• Sensory changes in the 4th and 5th digits

Diagnostic Evaluation

When evaluating suspected Saturday night palsy:

1. Clinical examination: Look for inability to extend the wrist, fingers, and thumb, with preserved finger flexion and grip strength. 3

2. Electrodiagnostic studies: These should be performed after approximately 2 weeks and typically show:

   • Delayed nerve conduction velocity of the radial nerve
   • Evidence of axonal loss in severe cases 3

3. Imaging: MRI is not typically required for straightforward cases but may be useful to exclude other causes of wrist drop. 4, 5

Differential Diagnosis

Important conditions to differentiate from Saturday night palsy include:

• Cervical radiculopathy: Presents with neck pain radiating to the arm with dermatomal sensory changes and myotomal weakness. MRI of the cervical spine would show nerve root compression. 4, 5

• Posterior cord brachial plexopathy: Affects multiple nerves including radial, causing more widespread deficits.

• Lead poisoning (saturnine palsy): Historically confused with Saturday night palsy due to similar presentation and name similarity. 1, 2

• Acute porphyrias: Can cause motor neuropathy with wrist and finger drop. 1

Management and Prognosis

The prognosis for Saturday night palsy is generally excellent:

• Improvement typically begins within 2-3 weeks 3
• Complete recovery occurs in most cases within 6 months 1
• Conservative management with wrist splinting and physical therapy is usually sufficient
• Surgical intervention is rarely necessary unless there is no improvement after 3-4 months

Common Pitfalls

1. Misdiagnosing as stroke or cervical radiculopathy: The sudden onset of wrist drop can be mistaken for a central nervous system problem. 3

2. Unnecessary imaging: Extensive imaging is often not required for typical cases with clear history of compression. 4, 5

3. Overlooking the historical context: The term "Saturday night palsy" likely evolved from "saturnine palsy" (lead poisoning), which has a similar clinical presentation. 2

4. Failing to recognize severe cases: While most cases resolve spontaneously, prolonged compression can lead to "Crush Syndrome" with rhabdomyolysis and potential renal failure. 6