Arthrogryposis multiplex congenita: histochemical study of biopsied muscles.

Morphometric analysis was performed after histochemical staining on 12 biopsied muscles of the affected limbs from 12 patients with arthrogryposis multiplex congenita. Except for one muscle, samples demonstrated variation in fiber size associated with abnormal fiber type distribution suggesting abnormal innervation: large groups of atrophic fibers in one muscle, either type 1 or 2 fiber predominance with occasional fiber type grouping in five, a complete lack of type 2 fibers in one, type one fiber atrophy in one, both type 2A and 2B fiber atrophy in two, and increased number of type 2C fibers in four. In most patients with arthrogryposis multiplex congenita, a defect in neural influence on the developing muscles may be responsible for the absence or maldevelopment of some muscle groups. Underdeveloped muscles are then assumed to induce imbalance of agonists and antagonists resulting in permanent contractures.