Neuromyotonic discharges are electrophysiologically characterised as bursts of motor unit potentials firing at more than 150 Hz for 0.5 to 2 seconds. The amplitude of the response typically wanes. Discharges may occur spontaneously or be initiated by needle movement.1 Walsh described a case of a mediastinal tumour and neuromyotonia with very high frequency discharges that outlasted voluntary effort.2

We report a case of an acquired paraneoplastic neuromyotonia associated with thymoma, clinically manifested myotonia-like muscle stiffness, and an unusual electrophysiological pattern of neuromyotonic discharges that were evoked voluntarily or with electrical stimulation but were absent spontaneously and were not elicited by needle displacement.

A 71 year old women presented with a 6 month history of muscle stiffness, paraesthesias provoked mostly by movement, disturbed speech, and difficult walking. At the time of examination she could not walk independently.

Clinical examination disclosed pronounced dysarthria and ataxic-like limb movement interrupted by superimposed tonic involuntary contractions. The muscle decontraction was prolonged and percussion myotonia was absent. Fasciculations and myokymia-like movements were seen in her arms, but occurred only sparsely and intermittently. The distal foot and hand muscles were slightly paretic and atrophic. Tendon reflexes were weak in the arms and absent in the legs. A decreased perception of vibration was present …