Electrophysiologic evidence for anterior horn cell disease in amyoplasia.

Amyoplasia is the most common subtype of arthrogryposis multiplex congenita. Children exhibit congenital muscle aplasia or hypoplasia, resulting in symmetric limb contractures that occur in a characteristic pattern. A high incidence of midforehead capillary hemangiomas, micrognathia, and minor genital anomalies also occurs with this disorder. The etiology and specific site of injury in amyoplasia remain unclear. Previous muscle biopsy and electrophysiologic studies could not differentiate between neurogenic or myogenic causes. We describe five children with amyoplasia. Four children demonstrated electrophysiologic features consistent with motor neuronopathy. A careful segmental needle electromyography study revealed variable involvement at different myotomes. We hypothesize that the anterior horn cell may represent the site of disease in a subset of children with amyoplasia.