Hereditary increased muscle mechanical irritability and progressive contracture with stretch-induced electromyographic activity.

A son and mother are reported with autosomal dominantly transmitted painless, increased mechanical irritability in the limb and trunk muscles and progressive finger contracture. Immediately after a tap, muscle swelling appeared. With light tapping, wavelike muscle surface movements appeared. Progressive contractures developed first in the proximal interphalangeal finger joints and subsequently involving the lower arm muscles. The contractures disappeared in the local curare test. No spontaneous activity was recorded on concentric needle recording. Serial repetitive activity was recorded with fine wire electrode recording, induced by muscle stretch, performed by percussion hammer blows or by prolonged finger grasp. A slight, irritative peripheral nervous lesion could be the cause. The chronic sensorimotor polyneuropathy may be also a part of the syndrome.