An unusual cause of swan neck deformity of the fingers.

OBJECTIVE To describe a patient who presented with nonfixed swan neck deformity of the fingers and generalized body aches. DESIGN Case report. SETTING Tertiary care teaching hospital. PATIENT A 38-year-old woman who presented with swan neck deformity of the fingers. MAIN OUTCOME MEASURES Electromyographic finding and electromyographic and clinical response to intravenous immunoglobulin. RESULTS Needle electromyography revealed continuous motor unit activity in the 50- to 70-Hz frequency during the resting state for all the muscles sampled, which suggests the possibility of neuromyotonia. After ruling out possible secondary causes, we treated the patient with intravenous immunoglobulin, considering primary neuromyotonia. The body ache improved by 100% on the visual analogue scale, and the electromyographic discharges disappeared from the paraspinal and tibialis anterior muscles and changed in its morphology to doublets, triplets, and multiplets in the first dorsal interossei and flexor digitorum profundus. CONCLUSION Neuromyotonia should be considered in the differential diagnosis of swan neck deformity of the fingers, especially in cases that show no fixed deformity and are not associated with any other rheumatologic stigmata.