Differential diagnosis between fibrodysplasia ossificans progressiva and childhood dermatomyositis with calcinosis.

Both fibrodysplasia ossificans progressiva (FOP) and childhood dermatomyositis with calcinosis are rare diseases, and present with ossifying or calcifying processes. Six cases of FOP and one case of childhood dermatomyositis with calcinosis are studied. All six FOP patients had the typical digital anomalies and the characteristic ectopic bone formation starting from the trunk. Calcification in the case of childhood dermatomyositis occurred in the limbs. A carefully differentiated diagnosis between these two diseases is needed, because they share common clinical and radiologic features, but require different management. Delay in the diagnosis of FOP is common, although early recognition of FOP prevents a child from accidental or iatrogenic injury, which can precipitate ectopic ossification. Surgical removal of the ectopic bone or release of the contracture in three FOP patients was followed by rapid recurrence. Entrapment neuropathy and a mild myopathic pattern in two FOP patients, who underwent nerve conduction and electromyographic studies, were secondary to ectopic bone formation. One FOP patient received a computed tomography examination which showed basal ganglia calcification. No coexistence of FOP and childhood dermatomyositis with calcinosis was found.