Pseudomyotonia in cervical myelopathy: A case report

A 68-year-old man began, a year ago, to complain of pain in the legs with frequent cramps, stiffness and increased difficulty in walking. Six months later, he started to experience pain in the arms, with difficulty in relaxing the fingers after a forceful contraction of hand muscles; this was more evident on the right. On admission, the neurological examination showed generalized myokymia in the limbs with increased tone, bilateral Hoffmann sign, spastic gait, and mild paralysis of the right leg. Dexter finger movements were impaired bilaterally. Fingers and wrist flexion of both hands were performed smoothly, but the subsequent extension was slower. This phenomenon was not evocable with percussion; however, it was exaggerated by repeated movements. It disappeared completely when the patient was asked to relax the flexed fingers rather than extend them actively. Cervical MRI showed a congenital reduction of the neurocanal, with posterior osteophytosis more evident at C3-C6 level, where the spinal medulla was strongly compressed and had a alteration of signal. We have studied with electrophysiological methods the so-called pseudomyoton- ic reaction, which is rarely associated with cervical myelopathy. Routine electromyographic records did not show myotonic discharges. After voluntary contraction of the right extensor digitorurn communis and flexor carpi radialis, there was a persistence of motor action potentials for a few milliseconds. We recorded the electromyographic surface activity from flexor-extensor forearm muscles of both arms simultaneously: during externally paced rapid movement of the left wrist we recorded a "mirror" activation of right extensor-flexor muscles with the same latency, but not vice versa. This might be due to a maladaptive reorganization along the corticospinal pathways. Transcranial magnetic stimulation of the brain revealed increased latency of motor evoked potentials from the abductor pollicis brevis (27.8 ms on the left side and 28.6 on the right side) with normal latency from cervical root stimulation, hence, resulting in an increased central conduction time (12.8 ms on the left side and 13.2 on the right side).