Muscular dystrophies (also called myopathies) are noninflammatory inherited disorders of progressive muscle weakness.
There are several types, distinguished by their inheritance patterns. Duchenne’s muscular dystrophy is an X-linked recessive disorder of young boys that is characterized by clumsy walking, decreasing motor skills, lumbar lordosis, and muscle weakness. The hip extensors are usually affected first. Muscle biopsy demonstrates foci of necrosis and connective tissue infiltration, with absence of the dystrophin protein and elevated creatine phosphokinase (CPK) on DNA testing. These individuals typically lose independent ambulation by age 10 and become wheel- chair dependent by age 15 years. They usually die of cardiorespiratory complications before age 20 years. Becker’s muscular dystrophy has a similar but less severe pathophysiology. Affected individuals also have an abnormal absence of dystrophin and histologic evidence of necrosis with connective tissue infiltration. However, they can often live beyond age 20 years without respiratory support. Other rare types of muscular dystrophy are seen in older individuals. Facioscapulohumeral muscular dystrophy is an autosomal dominant disorder seen in individuals between 6 and 20 years of age. They have facial muscle abnormalities, normal CPK, and winging of the scapula. Limb-girdle muscular dystrophy is an autosomal recessive disorder diagnosed in individuals be- tween 10 and 30 years of age and is characterized by pelvic or shoulder girdle involvement and elevated CPK.