Muscle biopsy in PAN shows –
**Core Concept**
Muscle biopsy is a diagnostic tool used to assess muscle damage and inflammation in various neuromuscular disorders, including Polyarteritis Nodosa (PAN). PAN is a systemic vasculitis that affects medium-sized arteries, leading to necrotizing inflammation and granuloma formation.
**Why the Correct Answer is Right**
In PAN, the muscle biopsy typically shows perivascular inflammation and necrotizing vasculitis, characterized by the presence of granulomas and fibrinoid necrosis around the affected blood vessels. This is due to the immune-mediated damage to the blood vessel walls, leading to ischemia and subsequent necrosis of the surrounding muscle tissue. The granulomas are formed as a result of the aggregation of immune cells, such as T lymphocytes and macrophages, in response to the antigenic stimulus.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately represent the typical histopathological findings in PAN. While muscle biopsy may show some degree of muscle damage, the characteristic perivascular inflammation and granulomas are not typically seen in other conditions like dermatomyositis.
**Option B:** This option is incorrect because it suggests a specific type of muscle fiber atrophy, which is not a hallmark feature of PAN. While muscle atrophy may occur in various neuromuscular disorders, it is not a diagnostic feature of PAN.
**Option C:** This option is incorrect because it implies a specific type of muscle injury, such as rhabdomyolysis, which is not typically associated with PAN. While muscle injury may occur in various conditions, it is not a characteristic feature of PAN.
**Clinical Pearl / High-Yield Fact**
A key feature of PAN is the presence of granulomas in the muscle biopsy, which can be distinguished from other conditions like dermatomyositis by the absence of significant muscle fiber atrophy and the presence of perivascular inflammation.
**Correct Answer:** C.