[Isolated finger flexion caused by continuous muscle fiber activity].

We report two patients who presented with progressive involuntary flexion of fingers. Both of them were women (Case 1 and 2 were 23 year old and 86 year old, respectively), and developed involuntary finger flexions, particularly of the ring and little fingers, following a localized pain of their hands and forearms. The other neurological findings were not present. There was no abnormal finding in their serum, and anti-voltage-gated potassium channel antibodies were negative. Nerve conduction velocity studies revealed no obvious peripheral neuropathy or conduction block. EMG studies revealed continuous muscle fiber activities only in the flexor digitorum superficialis muscles in both patients. Additionally, in Case 1, neuromyotonic discharges at frequencies of 100-200 Hz were recorded only from the flexor digitorum superficialis muscle. The present findings are likely to be similar to those of a novel form of focal neuromytonia reported recently as 'isolated finger flexion'.