Polyarteritis nodosa (PAN) is a vasculitis of small- and medium-sized vessels, characterized by vascular aneurysms that can lead to ischemia and infarction. We present the case of a patient with classic polyarteritis nodosa in abdominal organs who additionally demonstrated antitreponemal and antiphospholipid antibodies, resulting in a severe cerebral thrombosis. This case highlights: 1. The potential for false-positive syphilis serology in PAN patients, and 2. The rare coexistence of polyarteritis nodosa and the catastrophic antiphospholipid syndrome.