Calf pseudohypertrophy in Duchenne muscular dystrophy is primarily due to replacement of muscle by which tissues?

• A. Edema and inflammatory infiltrates within the muscle
• B. Adipose tissue infiltrating muscle but not fibrous tissue
• C. Fibrous tissue replacing muscle without fat
• D. Fat and fibrous tissue replacing muscle

Answer: (D)

Calf pseudohypertrophy in Duchenne muscular dystrophy happens because degenerating muscle fibers are progressively replaced with noncontractile tissue. In DMD, the lack of dystrophin leads to repeated cycles of muscle fiber death, and the muscle is gradually replaced not just by fat but also by fibrous connective tissue. This combination of fat and fibrous tissue expands the calf region, making it look larger while the muscle’s strength is actually decreased. Edema and inflammatory infiltrates describe an active, acute process, which isn’t the chronic replacement pattern seen in established pseudohypertrophy. Fat infiltration alone doesn’t capture the full, stiff, nonfunctional replacement that fibrous tissue adds, and fibrosis plus fat together best explain the enlargement with functional loss.