Isolated finger flexion: a novel form of focal neuromyotonia

Two almost identical elderly women are described who presented with gradually progressive painless involuntary flexion of the ring and middle fingers over 12 months, leading eventually to contractures. The flexion deformity persisted during sleep and was the sole neurological abnormality. Both patients had advanced chronic obstructive pulmonary disease and were on long term salbutamol and oxygen. Neurophysiological studies indicated that this was due to neuromyotonia mainly involving flexor digitorum superficialis muscles without evidence of underlying peripheral neuropathy, proximal conduction block, or generalised neuromyotonia. Voltage gated potassium channel antibodies were negative. The clinical and neurophysiological picture remained static over a 2 year follow up period. It is suggested that this is a novel form of acquired focal neuromyotonia and speculate both on its cause and distribution.