[Nemaline myopathy with type 2 fiber predominance; a case report]

A 4-year-old boy was admitted to our hospital because of dyspnea and muscle-weakness. His developmental milestones were delayed. His face was long with opened mouth. He spoke with nasal voice. He had proximally dominant muscle weakness and his deep tendon reflexes were absent. Laboratory examination revealed normal serum creatine kinase level and a myopathic EMG pattern. Blood gas analysis revealed metabolic acidosis with PH 7.35, PCO2 55.4 mmHg, PO2 62.4 mmHg, BE 3.0, probably from the metabolic acidosis by respiratory muscle weakness. In the biopsied left biceps brachii muscle, there were scattered fibers with nemaline bodies and abnormal fiber type distribution; type 1, 2 A, 2 B and 2 C fibers comprised 7%, 70%, 21% and 2% respectively. Small type 1 fibers and type 1 fiber predominance are the characteristic and common histochemical findings in nemaline myopathy. Accordingly, type 2 fiber predominance in the present patient is a unique, rare phenomenon. The finding might result from a preferential loss of type 1 motoneurons or muscle fiber type transformation from type 1 to type 2 fibers due to a certain abnormal neuronal influence on developing muscles.