Type 2 Muscle Fiber Predominance: A Case Report

Abstract

Skeletal muscles are a heterogeneous group of tissues categorized into different fiber types.1 These fibers are divided into slow-twitch type 1 and fast-twitch type 2 fibers, which are identified by their expression of specific myosin heavy chain isoforms.5,7,9 The predominance of type 2 muscle fibers has been observed in various diseases involving skeletal muscle such as Duchenne muscular dystrophy, hyperthyro-idism, and type 2 muscle fiber predominance.2,4 Type 2 muscle fiber predominance is a rare muscular disease whose primary manifestations include proximal muscle weakness, exertional myalgia, fasciculations, and episodes of prolonged painful muscle cramping.3,4 These symptoms eventually led our patient to be wheel-chair bound with subsequent disuse muscle atrophy. In this case we describe a patient with type 2 muscle fiber predominance, the progression of his disease, and his experience in our inpatient rehabilitation facility.