Perifascicular atropy of muscle fibres is seen in
**Core Concept**
Perifascicular atrophy of muscle fibers refers to a specific pattern of muscle damage characterized by the selective loss of muscle fibers at the periphery of the fascicle, which is a group of muscle fibers surrounded by a connective tissue sheath. This condition is often associated with muscle diseases that affect the muscle's blood supply or the muscle's contractile function.
**Why the Correct Answer is Right**
Perifascicular atrophy is a hallmark feature of dermatomyositis, a type of inflammatory muscle disease that affects the muscle's blood supply and leads to muscle weakness and atrophy. The condition is thought to result from the inflammation of the capillaries and small blood vessels that supply the muscle, leading to ischemia and muscle fiber death. The perifascicular location of the atrophy is due to the fact that the capillaries and small blood vessels are more densely packed at the periphery of the fascicle.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because perifascicular atrophy is not typically associated with polymyositis, another type of inflammatory muscle disease that primarily affects the muscle's contractile function rather than its blood supply.
**Option B:** This option is incorrect because perifascicular atrophy is not a characteristic feature of inclusion body myositis, a type of muscle disease that primarily affects the muscle's contractile function and is associated with the presence of abnormal protein deposits within the muscle fibers.
**Option C:** This option is incorrect because perifascicular atrophy is not typically associated with muscular dystrophy, a group of genetic muscle diseases that primarily affect the muscle's contractile function rather than its blood supply.
**Clinical Pearl / High-Yield Fact**
Perifascicular atrophy is a key diagnostic feature of dermatomyositis, and its presence should prompt a careful evaluation for this condition, particularly in patients with muscle weakness and characteristic skin changes.
**Correct Answer: A. Dermatomyositis.**