Cubital tunnel syndrome is a rare condition causing compression of the ulnar nerve, resulting in neuropraxia as the nerve transverses the cubital tunnel of the elbow. Symptoms typically include numbness and/or tingling of the pinky and ulnar half of the ring finger and, in more severe cases, may cause weakness of muscles innervated by the ulnar nerve, namely the thenar, hypothenar, interossei, and the lumbrical muscles (intrinsics). 

Causes of cubital tunnel syndrome include osteoarthritis related to prior fracture, tumor/cysts, and excessive leaning on the elbow. The differential diagnosis typically requires elimination of other causes of ulnar nerve dysfunction such as cervical radiculopathy. Cervical radiculopathy will sometimes occur without neck pain but it typically affects the whole ring finger rather than only the ulnar side. Symptoms of a brachial plexus injury will include numbness of a whole finger, and ulnar tunnel syndrome involves wrist pain rather than elbow pain.

Treatment of cubital tunnel syndrome depends on the underlying cause. Low-dose, short-term steroids and halting any activity that aggravates the condition may be an effective treatment when the cause is temporary or reversible. When there is anatomic compression that cannot be relieved by activity modification, such as bone growth or an enlarging cyst, surgery will likely be required to reduce pressure on the radial nerve. Even after treatment, neuropraxia can take up to 6 months to resolve.


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Outcome

In this case, an outpatient magnetic resonance imaging (MRI) showed an acute on chronic tear of the common flexor tendon at the medial humeral epicondyle. The MRI also confirmed advanced hypertrophic osteoarthritis at the elbow causing partial effacement of the cubital tunnel. 

Clinical Pearl

When a patient presents with half of the ring finger numb (along with other fingers), this usually means that the ulnar or median nerve is involved rather than a spinal nerve.

Brady Pregerson, MD, is an emergency physician at Tri-City Medical Center in Oceanside, California, and at Scripps Coastal Urgent Care in Oceanside, California.

Reference

Pregerson DB. Nerve injuries. In: Emergency Medicine 1-Minute Consult Pocketbook. 5th ed. 2017;5. http://www.erpocketbooks.com/emergency_medicine_reference_books/quick-essentials-emergency-medicine/