Muscle hypertrophy in Duchenne muscular dystrophy. A pathological and morphometric study

Area of Science:

• Neurology
• Pathology
• Muscle Biology

Background:

• Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by progressive muscle degeneration.
• Muscle hypertrophy, particularly in the calf muscles, is a common clinical feature in DMD, but its pathological basis is not fully understood.

Purpose of the Study:

• To investigate the pathological basis of apparent muscle hypertrophy in Duchenne dystrophy.
• To compare the pathological and histochemical changes in gastrocnemius muscles (with apparent hypertrophy) and vastus lateralis muscles (atrophied) in DMD patients.

Main Methods:

• Semi-quantitative assessment of pathological and histochemical changes in muscle biopsy specimens.
• Comparison of 9 gastrocnemius and 7 vastus lateralis biopsies from DMD patients aged 4-11 years.
• Evaluation of hypercontracted fibers, endomysial fibrosis, fat infiltration, fiber type differentiation, and fiber diameter.

Main Results:

• Quadriceps muscles showed significantly higher numbers of hypercontracted fibers, endomysial fibrosis, and fat infiltration compared to gastrocnemius muscles.
• Gastrocnemius muscles exhibited better fiber type differentiation and increased mean fiber diameter (above normal), but also increased fat-fibrosis.
• Early fiber hypertrophy in quadriceps progressed to atrophy in older patients, while gastrocnemius showed persistent fiber hypertrophy despite increased fat-fibrosis.

Conclusions:

• The apparent calf muscle hypertrophy in DMD is not true hypertrophy but rather a combination of increased fat and fibrosis.
• The dystrophic process is more active in the quadriceps muscles than in the gastrocnemius muscles.
• Persistent fiber hypertrophy in the gastrocnemius may relate to postural abnormalities observed in Duchenne dystrophy.