**Core Concept**
Perifascicular atrophy, a hallmark of dermatomyositis, refers to the selective degeneration and atrophy of muscle fibers located at the periphery of muscle fascicles. This phenomenon is a result of the inflammatory and autoimmune processes that characterize dermatomyositis.

**Why the Correct Answer is Right**
Dermatomyositis is an inflammatory muscle disease characterized by the presence of autoantibodies and perifascicular atrophy. The perifascicular atrophy is thought to occur due to the presence of complement and immune complexes at the periphery of the muscle fascicles, leading to damage and atrophy of the surrounding muscle fibers. The perifascicular distribution is a result of the muscle's blood supply, with the end-arterial circulation of the muscle leading to a greater susceptibility to ischemia and damage in the perifascicular region.

**Why Each Wrong Option is Incorrect**
**Option A:** Steroid myopathy, on the other hand, typically presents with type II fiber atrophy and does not exhibit perifascicular atrophy.

**Option B:** Inclusion body myositis is characterized by endomysial inflammation and the presence of inclusion bodies within the muscle fibers, but it does not typically present with perifascicular atrophy.

**Option D:** Viral myositis can cause inflammation and damage to muscle fibers, but it does not specifically exhibit perifascicular atrophy.

**Clinical Pearl / High-Yield Fact**
Perifascicular atrophy is a key histopathological feature of dermatomyositis, and its presence can help differentiate this condition from other myopathies.

**Correct Answer:**
✓ Correct Answer: A. Dermatomyositis