Muscle fibre type changes in hypothyroid myopathy

Abstract

Changes in muscle fiber type in hypothyroid myopathy were studied by serial percutaneous needle biopsy of vastus lateralis before and during treatment with L thyroxine. A type II fiber atrophy and loss was found, which correlated with the clinical and biochemical evidence of a myopathy. The type II fiber atrophy was corrected by L thyroxine but type II fiber loss was still apparent in severely myopathic patients up to two years after starting treatment. The pathogenesis and significance of type II fiber atrophy and loss are discussed in relation to prognosis.