What is the definitive diagnostic test for Polyarteritis nodosa?

The definitive diagnostic test for Polyarteritis nodosa (PAN) is a vessel biopsy, particularly when performed during angiography. This condition is characterized by systemic vasculitis affecting medium-sized muscular arteries, which can lead to ischemia and necrosis in various organs. A vessel biopsy allows for the direct examination of the inflamed artery to observe the characteristic fibrinoid necrosis and the presence of inflammatory cell infiltrates, which are pivotal in confirming the diagnosis.

While MRI, skin biopsy, and serological tests can provide valuable information, they do not provide the direct evidence needed to confirm the diagnosis of PAN. MRI can show changes in the affected tissues but lacks the specificity required for a definitive diagnosis of vasculitis. Skin biopsy is often used to evaluate cutaneous manifestations of vasculitis but is not adequate for diagnosing systemic involvement. Serological tests might reveal markers of inflammation or certain antibodies but are not specific for Polyarteritis nodosa itself, thus cannot confirm the diagnosis. The vessel biopsy remains the most definitive approach for diagnosing this complex condition.