Diagnosis: Cubital Tunnel External Compression Syndrome (Ulnar Neuropathy)
The diagnosis is cubital tunnel external compression syndrome, a form of ulnar nerve entrapment caused by prolonged direct pressure on the ulnar nerve at the elbow from leaning on hard surfaces. 1, 2
Clinical Presentation
The classic presentation includes:
- Local tenderness over the cubital tunnel (the groove on the inner/medial aspect of the elbow where the ulnar nerve passes) 3
- Paresthesias (tingling/numbness) in the ring and little fingers, often with sudden onset 3, 4
- Resting pain in the proximal forearm that may radiate distally 4
- Neurological deficit in ulnar nerve distribution while typically sparing the flexor digitorum profundus and flexor carpi ulnaris muscles (these are spared because their nerve branches arise proximal to the compression site) 3
Diagnostic Confirmation
Start with plain radiographs of the elbow to rule out bony pathology, fractures, or heterotopic ossification that could mimic or contribute to nerve compression. 5, 6
If radiographs are normal or nonspecific:
- Dynamic ultrasound is the preferred initial advanced imaging to directly visualize ulnar nerve subluxation during elbow flexion and assess nerve cross-sectional area/thickness with high accuracy. 1
- T2-weighted MR neurography serves as the reference standard if ultrasound is inconclusive, showing characteristic high signal intensity and nerve enlargement. 5, 1
- Electromyography and nerve conduction studies help confirm the diagnosis in atypical presentations and differentiate between demyelinating versus axonal injury patterns. 1, 3
Pathophysiology
This condition represents the subacute form of ulnar nerve compression at the elbow, distinct from chronic cubital tunnel syndrome. 2 The external pressure from prolonged elbow contact with hard surfaces (tables, armrests) compresses the ulnar nerve within the cubital tunnel, leading to ischemia and nerve dysfunction. 2, 3 A compressed nerve becomes more sensitive to subsequent ischemia from additional pressure, creating a cycle of worsening symptoms. 2
Critical Differential Considerations
While cubital tunnel external compression syndrome is the primary diagnosis, be aware that:
- Olecranon bursitis can coexist and presents with posterior elbow swelling and pain, diagnosed through bursal fluid analysis if infection is suspected. 6, 7
- Medial epicondylitis (golfer's elbow) causes pain at the medial epicondyle itself (not the cubital tunnel) with resisted wrist flexion/pronation. 8
- Anconeus epitrochlearis muscle (present in up to 34% of people) can cause similar symptoms but typically presents in younger patients with more rapid progression, distinct velocity drop on nerve conduction studies, and muscle edema on MRI. 9
Common Pitfalls to Avoid
- Never proceed directly to surgery without a 3-6 month conservative trial unless significant motor weakness or muscle atrophy is present. 1
- Do not rely on corticosteroid injections as first-line treatment—unlike tendinopathy, injections are not recommended as primary therapy for nerve compression. 1
- Avoid positions that flex the elbow beyond 90 degrees during the conservative treatment period, as this increases compression and subluxation risk. 1
- Never use padding that is too tight, as this creates a tourniquet effect and paradoxically worsens compression. 1