Neurology · Peripheral Nerve Disorders
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The most common site of ulnar nerve entrapment is the cubital tunnel at the medial epicondyle of the elbow.
Patients typically present with paresthesias and sensory loss involving the fifth digit and the ulnar half of the fourth digit.
Advanced cases manifest as intrinsic hand muscle atrophy, specifically the interossei and hypothenar eminence, leading to a claw hand deformity.
The Froment sign is positive when the patient compensates for adductor pollicis weakness by flexing the flexor pollicis longus during a paper-pulling test.
Physical examination reveals weakness in finger abduction and adduction and weakness in wrist flexion/adduction.
Diagnosis is confirmed via electromyography (EMG) and nerve conduction studies (NCS) showing decreased conduction velocity across the elbow.
Initial management for mild cases includes nocturnal elbow splinting in extension and avoidance of repetitive elbow flexion.
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A 45-year-old male construction worker presents with a 3-month history of numbness and tingling in his left small finger and ring finger. He reports that his symptoms worsen when he is working and keeping his elbow bent for long periods. On physical exam, there is atrophy of the dorsal interossei muscles and the hypothenar eminence. When asked to hold a piece of paper between his thumb and index finger, he exhibits flexion of the interphalangeal joint of the thumb to maintain the grip.
What is the most likely diagnosis and the name of the physical exam finding described?
Ulnar neuropathy at the cubital tunnel; Froment sign.
The patient's sensory distribution and intrinsic muscle atrophy are classic for ulnar nerve entrapment at the elbow, and the compensatory thumb flexion is the pathognomonic Froment sign.
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Etiology / Epidemiology
Most common at the cubital tunnel due to prolonged elbow flexion or repetitive trauma.
Clinical Manifestations
Paresthesias in the 4th and 5th digits with Froment's sign and intrinsic muscle wasting.
Diagnosis
Electromyography (EMG) and Nerve Conduction Studies (NCS) are the gold standard for localization.
Treatment
Night splinting in extension is first-line; avoid repetitive elbow flexion.
Prognosis
Early intervention prevents permanent claw hand deformity; surgical success depends on nerve conduction velocity recovery.
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Epidemiology & Etiology
Ulnar neuropathy is the second most common entrapment neuropathy after carpal tunnel syndrome. It is frequently seen in patients with occupational repetitive flexion or those who lean on their elbows. Chronic compression at the cubital tunnel is the primary etiology.
Pertinent Anatomy
The ulnar nerve passes posterior to the medial epicondyle within the cubital tunnel. It innervates the flexor carpi ulnaris and the intrinsic muscles of the hand, including the interossei and the adductor pollicis.
Pathophysiology
Compression leads to focal demyelination followed by axonal degeneration. Prolonged flexion increases pressure within the cubital tunnel, causing ischemia to the nerve. Chronic injury results in denervation of the intrinsic hand muscles, leading to the classic ulnar claw deformity.
Clinical Manifestations
Patients present with numbness and tingling in the 4th and 5th digits. Physical exam reveals Froment's sign (compensatory thumb IP flexion during paper-pull test) and atrophy of the first dorsal interosseous muscle. Red flags include sudden onset or associated trauma, which may indicate a fracture or hematoma.
Diagnosis
Nerve Conduction Studies (NCS) confirm the diagnosis by demonstrating slowed conduction velocity across the elbow. Electromyography (EMG) is used to assess for denervation in the ulnar-innervated muscles. Imaging is reserved for suspected masses or bony abnormalities.
Treatment
Conservative management includes night splinting in extension and elbow pads to prevent direct pressure. Avoid prolonged elbow flexion during daily activities. If conservative measures fail after 3-6 months or if there is progressive muscle wasting, surgical ulnar nerve transposition is indicated.
Prognosis
Mild cases often resolve with conservative therapy. Severe cases with intrinsic muscle atrophy have a poorer prognosis for full motor recovery. Monitoring requires serial clinical exams to assess for worsening motor deficits.
Differential Diagnosis
C8 radiculopathy: involves sensory loss in the medial forearm and weakness in non-ulnar muscles
Thoracic outlet syndrome: involves diffuse arm pain and vascular symptoms
Guyon canal syndrome: spares the dorsal cutaneous sensory branch
Medial epicondylitis: presents with localized pain without sensory deficits
Brachial plexopathy: involves multiple nerve distributions