Snapshot A 2-year-old boy presents with fatigue and difficulty with walking. The mother describes her child as “clumsy,” as he usually falls while walking. The mother also reports difficultly with climbing the stairs, which is new. The mother recalls that a relative died in his teens and also experienced muscle weakness when he was very young. On physical exam, there is weakness in the proximal muscles of the lower extremity, bilateral enlargement of the calves, and a positive Gower sign. (Duchenne muscular dystrophy) Introduction Clinical definition inherited disorder of skeletal muscle leading to progressive muscle weakness Epidemiology Incidence Duchenne muscular dystrophy most common early onset form Becker muscular dystrophy a relatively common form that typically presents later in life Demographics male children recall that males have only one X-chromosome Etiology X-linked recessive mutation in the dystrophin gene Duchenne muscular dystrophy frameshift or deletion of the dystrophin gene login to view 1 more bullet Becker muscular dystrophy non-frameshift login to view 2 more bullets Pathogenesis Normal biology dystrophin is one of the largest human genes and appears to be involved in preventing muscle fiber degeneration by providing mechanical stability between the myofiber and its cell membrane login to view 1 more bullet cell signaling dystrophin is expressed in cardiac, skeletal, and neural tissue Pathology absent or decreased function of dystrophin leads to cycles of muscle fiber degeneration and regeneration this subsequently leads to fatty replacement and a distorted fascicular architecture Presentation Symptoms progressive muscle weakness most severe in the proximal muscles and lower extremity waddling gait Physical exam Gower sign a patient using their upper extremity to stand login to view 1 more bullet calf pseudohypertrophy lumbar lordosis hypo- or areflexia DMD onset age 3-6 vs BMD onset in adolescence Studies Creatine kinase elevated Genetic analysis gold standard if negative, do muscle biopsy Muscle biopsy degeneration and regeneration muscle replacement by fat and connective tissue Immunostaining absent dystrophin Differential Limb-girdle muscular dystrophy Spinal muscular atrophy Becker muscular dystrophy Treatment Approach to management treatment for both Duchenne and Becker muscular dystrophy is multidisciplinary to manage symptoms and complications e.g., physical therapy to maintain ambulation and prevent contractures Medical glucocorticosteroids indication login to view 1 more bullet drugs login to view 2 more bullets adverse effects login to view 3 more bullets Complications Muscular wheel chair bound Cardiac dilated cardiomyopathy arrhythmia especially with BMD Orthopedic fractures secondary to falling Prognosis Duchenne muscular dystrophy mean age of death is 25 to 30 years of age secondary to heart failure respiratory failure Becker muscular dystrophy less severe than Duchenne muscular dystrophy