A Chinese boy with a DYT1 gene mutation presented with muscle stiffness, painful muscle spasms, myoclonus, and dystonia, compatible with stiff child syndrome, and is reported from Queen Mary Hospital, the University of Hong Kong. Stiffness of the left ankle began at age 4 years and spread to the right lower limb over a few months. Severely painful muscle spasms of the lower limbs developed 1 year later, and gradually extended to the trunk. Spasms were abolished by rectal diazepam 5 mg, and they decreased with sleep. EMG showed normal motor unit potentials on exertion, and continuous motor uinit activity during muscles spasms. Nerve conduction studies, and MRI of brain and spinal cord were normal. Improvement followed plasmapheresis, with 75% reduction in painful muscle spasms within 4 weeks. One year later, he developed progressive dystonia and painful muscle spasms, becoming wheelchair bound at age 7 years. After a third plasmapheresis, and treatment with baclofen, Artane, clobazam, and gabapentin, muscle spasms were partially controlled, and he is maintained on baclofen. Analysis of the DYT1 gene mutation was prompted by the appearance of dystonia, and his asymptomatic mother has the same mutation. 
COMMENT. The “stiff man” syndrome was first described by Moersch FP and Woltman HW, at the Mayo Clinic . I recall a 7-year-old, African-American, male child with the syndrome at Children’s Memorial Hospital, Chicago, in 1964; he responded partially to oral diazepam; the pathology was thought to be located in the spinal cord interneurons. The syndrome is rare in children, and has been described in newborns . The present authors recommend screening for DYT1 mutation in a child with muscle stiffness or spasms. Stiff child syndrome is distinguished from Isaac’s syndrome, characterized by muscle stiffness and cramps, with myokymia and fasciculations, and evidence of terminal motor fiber abnormality.