What is the most likely cause of right arm numbness that occurs at rest and resolves with movement, and what evaluation and management steps are recommended?

Right Arm Numbness at Rest, Relieved by Activity

Most Likely Diagnosis

This presentation is most consistent with a positional nerve compression syndrome, specifically radial nerve compression ("Saturday night palsy") or ulnar nerve entrapment, rather than cervical radiculopathy or vascular pathology. 1, 2

The key distinguishing feature—symptom relief with movement rather than worsening—points away from typical nerve root compression and toward mechanical compression that is position-dependent. 2

Clinical Reasoning

Why This Pattern Suggests Peripheral Nerve Compression

• Positional nerve compression causes symptoms at rest when the nerve is compressed against a hard surface or stretched in certain positions, with relief occurring when the limb is moved and the compression is released 2
• Radial neuropathy classically presents with numbness on the dorsum of the 1st to 3rd fingers and can occur from sleeping with arms in abnormal positions, hanging over armrests, or compression against surfaces 2
• Ulnar nerve entrapment is 7-10 times less common than radial compression in this presentation pattern but should be considered, particularly if symptoms involve the 4th and 5th fingers 1

Why Cervical Radiculopathy is Less Likely

• Cervical radiculopathy typically worsens with activity and neck movements, not improves 3, 4
• Pain radiating from the neck is the hallmark of cervical radiculopathy, along with dermatomal sensory changes 3, 4
• Most cervical radiculopathy patients report painful neck movements and muscle spasm as the most common examination findings 3

Critical Red Flags to Exclude

Immediately assess for these alarm symptoms that would require urgent imaging: 1, 5, 6

• Bilateral symptoms (suggests cervical myelopathy or central cord syndrome) 5, 6
• Progressive weakness in legs or arms 1, 5
• Unsteady gait or legs giving way 1, 5
• Numbness radiating from chest, groin, or involving lower extremities 1, 5
• Neck or back pain that worsens when lying down 1, 6
• Rapidly progressive or multifocal symptoms (suggests Guillain-Barré syndrome or vasculitis) 1

Diagnostic Evaluation

Initial Clinical Assessment

Perform focused neurological examination including: 1, 6

• Sensory distribution mapping: Radial nerve affects dorsum of thumb/index/middle fingers; ulnar nerve affects 4th and 5th fingers 2
• Motor strength testing: Wrist drop suggests radial neuropathy; finger abduction weakness suggests ulnar neuropathy 2
• Deep tendon reflexes: Diminished triceps reflex is most common in cervical radiculopathy if present 3
• Provocative testing: Spurling test, shoulder abduction test for cervical pathology 3

Imaging and Electrodiagnostic Studies

Imaging is NOT required initially unless red flags are present: 3

• History of trauma 3
• Persistent symptoms beyond 4-6 weeks 3
• Any red flag symptoms for malignancy, myelopathy, or abscess 3

Electrodiagnostic testing (EMG/NCS) should be performed after 2 weeks if diagnosis is unclear to differentiate peripheral neuropathy from cervical radiculopathy 2, 1

• Delayed nerve conduction velocity confirms peripheral nerve compression 2
• EMG has clinical utility when peripheral neuropathy is the likely diagnosis rather than cervical pathology 3

If cervical pathology is suspected based on red flags, MRI of the cervical spine is the first-choice imaging modality 6

Metabolic Screening

Consider screening laboratories if symptoms are bilateral or progressive: 1

• Glucose/HbA1c (diabetes) 1
• Thyroid function (hypothyroidism) 1
• Vitamin B12 level 1
• Renal function 1

Management Approach

Conservative Management (First-Line)

Reassure the patient that most cases of positional nerve compression resolve spontaneously within several weeks: 2

• Improvement typically begins after a mean of 2.4 weeks for radial neuropathy 2
• Avoid prolonged positioning of joints at end range and modify sleep positioning 6
• Ergonomic workplace assessment to identify and eliminate compression sources 6

Pharmacologic Treatment

If neuropathic symptoms (numbness, tingling) are bothersome, duloxetine is first-line pharmacologic treatment: 6, 5

• Supported by Level IB evidence for neuropathic symptoms 5

NSAIDs and muscle relaxants can be offered if there is associated musculoskeletal pain 3

When to Escalate Care

Refer to neurology or neurosurgery if: 6

• No improvement after 4-6 weeks of conservative management 3
• Progressive motor weakness develops 1, 5
• Any red flag symptoms emerge 1, 5, 6
• Bilateral symptoms develop 5, 6

MRI within 12 hours is required if clinical suspicion of cord compression exists 5, 6

Common Pitfalls to Avoid

• Do not assume unilateral arm numbness is always benign—always screen for red flag symptoms that indicate central pathology 1, 5
• Do not order MRI reflexively—imaging is not required unless red flags are present or symptoms persist beyond 4-6 weeks 3
• Do not delay urgent imaging if bilateral symptoms or myelopathy signs are present—this can lead to irreversible neurological damage 5
• Do not confuse the pattern: Symptoms that worsen with activity suggest radiculopathy; symptoms that improve with activity suggest positional compression 3, 4, 2