Pathogenesis and electrodiagnosis of cubital tunnel syndrome.

BACKGROUND: Cubital tunnel syndrome is a well-recognized clinical condition and is the second most common peripheral compression neuropathy. This study was designed to investigate the causes of cubital tunnel syndrome by surgical means and to assess the clinical value of the neurophysiological diagnosis of cubital tunnel syndrome. METHODS: Twenty-one patients (involving a total of 22 limbs from 16 men and 5 women, aged 22 to 63, with a mean age of 49 years) with clinical symptoms and signs indicating a problem with their ulnar nerve underwent motor conduction velocity examinations at different sites along the ulnar nerve and examinations of sensory conduction velocity in the hand, before undergoing anterior transposition of the ulnar nerve. RESULTS: Electromyographic abnormalities were seen in 21 of 22 limbs [motor nerve conduction velocity (MCV) range (15.9 - 47.5) m/s, mean 32.7 m/s] who underwent motor conduction velocity examinations across the elbow segment of the ulnar nerve. Reduced velocity was observed in 13 of 22 limbs [MCV (15.7 - 59.6) m/s, mean 40.4 m/s] undergoing MCV tests in the forearms. An absent or abnormal sensory nerve action potential following stimulation was detected in the little finger of 14 of 22 limbs. The factors responsible for ulnar compression based on observations made during surgery were as follows: 15 cases involved compression by arcuate ligaments, muscle tendons, or bone hyperplasia; 2 involved fibrous adhesion; 3 involved compression by the venous plexus or a concurrent thick vein; 2 involved compression by cysts. CONCLUSIONS: Factors inducing cubital tunnel syndrome include both common factors that have been reported and rare factors, involving the venous plexus, thick veins, and cysts. Tests of motor conduction velocity at different sites along the ulnar nerve should be helpful in diagnosis cubital tunnel syndrome, especially MCV tests indicating decreased velocity across the elbow segment of the ulnar nerve.