Congenital fiber type disproportion

Type I muscle fiber atrophy in childhood can be encountered in a variety of neuromuscular disorders. Congenital fiber type disproportion (CFTD) is one such condition which presents as a nonprogressive muscle weakness. The diagnosis is often made after excluding other differential diagnostic considerations. We present a 2-year-9-month-old full term boy who presented at 2 months with an inability to turn his head to the right. Over the next couple of years, he showed signs of muscle weakness, broad based gait and a positive Gower’s sign. He had normal levels of creatine kinase and normal electromyography. A biopsy of the vastus lateralis showed a marked variation in muscle fiber type. The adenosine triphosphate (ATP)-ase stains highlighted a marked type I muscle atrophy with rare scattered atrophic type II muscle fibers. No abnormalities were observed on the nicotinamide adenine dinucleotide (NADH), succinate dehydrogenase (SDH) or cytochrome oxidase stained sections. Ragged red fibers were not present on the trichrome stain. Abnormalities of glycogen or lipid deposition were not observed on the periodic acid–Schiff or Oil-Red-O stains. Immunostaining for muscular dystrophy associated proteins showed normal staining. Ultrastructural examination showed a normal arrangement of myofilaments, and a normal number and morphology for mitochondria. A diagnosis of CFTD was made after excluding other causes of type I atrophy including congenital myopathy. The lack of specific clinical and genetic disorder associated with CFTD suggests that it is a spectrum of a disease process and represents a diagnosis of exclusion.