Which condition is characterized by proximal muscle weakness with pseudohypertrophy and a positive Gower sign?

• A. Duchenne muscular dystrophy
• B. Spinal muscular atrophy
• C. Myotonic dystrophy
• D. Becker muscular dystrophy

Answer: (A)

Proximal muscle weakness with calf pseudohypertrophy and a positive Gower sign points to a dystrophinopathy that begins in childhood. In Duchenne muscular dystrophy, a mutation leads to absent or nonfunctional dystrophin, a protein that normally stabilizes muscle cell membranes during contraction. Without dystrophin, muscle fibers are damaged and gradually replaced by fat and connective tissue, causing the calves to look enlarged (pseudohypertrophy) even though the muscles are weakened. The weakness mainly affects proximal hip and thigh muscles, so children have trouble getting up from the floor and use their arms to push up (Gower sign).

This contrasts with other conditions: spinal muscular atrophy is a motor neuron disease with muscle atrophy rather than fatty replacement and the typical pseudohypertrophy and Gower maneuver are not defining features; myotonic dystrophy features myotonia (delayed muscle relaxation) and often distal weakness with systemic findings; Becker muscular dystrophy has a dystrophin mutation like Duchenne but with later onset and a slower, milder progression.