Question

A mother brings her 5-year-old boy, who has a 2-year history of progressive muscle weakness, to the pediatrician. She notices that the boy has trouble moving himself from a sitting position to a standing position and that he has to push off of the floor or pull himself up in order to stand. Physical examination reveals a happy boy with normal height and weight, normal reflexes, and large calves. A biopsy of his gastrocnemius would most likely show which of the following?

A. Fibrofatty replacement of muscle fibers
B. Increased proportion of slow-twitch red muscle fibers
C. Massive necrosis of all muscle fibers
D. Unusually high capillary density
E. Hypertrophy of fast-twitch white muscle fibers

Answer 1

In the case of the 5-year-old boy with progressive muscle weakness and enlarged calves, a biopsy of his gastrocnemius muscle would most likely show fibrofatty replacement of muscle fibers, indicative of Duchenne muscular dystrophy (DMD).

Step-by-step explanation:

A mother brings her 5-year-old boy, who has a 2-year history of progressive muscle weakness, to the pediatrician. She notices that the boy has trouble moving himself from a sitting position to a standing position and that he has to push off of the floor or pull himself up to stand. Physical examination reveals a happy boy with normal height and weight, normal reflexes, and large calves. A biopsy of his gastrocnemius would most likely show A. Fibrofatty replacement of muscle fibers.

This is suggestive of Duchenne muscular dystrophy (DMD), a genetic disorder characterized by progressive muscle degeneration and weakness. Due to a mutation that prevents the production of dystrophin, a protein essential for muscle function, muscle fibers are damaged and over time replaced with fibrous, fatty tissue, reflecting the fibrofatty replacement observed in the biopsy.