Hereditary continuous muscle fiber activity is a rare, non-dystrophic myopathy characterized by generalized myokymia and increased muscle tone associated with delayed motor milestones, leg stiffness, spastic gait, hyperreflexia and Babinski sign. Symptoms may be worsened by febrile illness or anesthesia. The disease is MONDO_0019943 (hereditary continuous muscle fiber activity). Also known as: continuous muscle fiber activity hereditary, continuous muscle fiber activity, hereditary, continuous muscle fibre activity hereditary, continuous muscle fibre activity, hereditary.