Polyarteritis nodosa and antiphospholipid syndrome: a systematic review of a rare and challenging overlap between vasculitis and thrombotic vasculopathy

BACKGROUND: The coexistence of polyarteritis nodosa (PAN) and antiphospholipid syndrome (APS) is rarely reported and remains poorly characterized. Both conditions may involve vascular injury, but through distinct mechanisms-necrotizing inflammation in PAN and thrombotic vasculopathy in APS. Their overlap may result in a unique and potentially severe clinical phenotype, posing diagnostic and therapeutic challenges. In addition, differentiating inflammatory vasculitic injury from thrombotic vascular occlusion may be particularly difficult in this overlap setting, especially in patients with catastrophic presentations. OBJECTIVE: To systematically review all published cases describing the association between PAN and APS, focusing on clinical features, laboratory findings, pathophysiological insights, management strategies, and outcomes. METHODS: A systematic search was conducted in PubMed/MEDLINE, Scopus, and Web of Science from inception through 2026. The search included terms related to "polyarteritis nodosa" and "antiphospholipid syndrome." Only studies reporting cases fulfilling accepted diagnostic or classification criteria for PAN and APS were included. Data extraction encompassed demographic characteristics, temporal relationship between diseases, clinical manifestations, antiphospholipid antibody profiles, imaging and histopathological findings, treatments, and outcomes. Due to heterogeneity and limited sample size, a descriptive analysis was performed. Because of the rarity of this overlap syndrome, the available evidence consisted predominantly of case reports and small case series, which were critically analyzed within a systematic review framework. RESULTS: A small number of cases were identified, all reported as case reports or small case series. Most patients were middle-aged males, although one pediatric case was described. The temporal relationship varied, with simultaneous diagnosis being most common, while in some cases APS developed after PAN onset. Clinically, patients exhibited features of systemic PAN, including visceral involvement, neuropathy, and hypertension, alongside thrombotic events characteristic of APS, such as arterial occlusions, renal infarctions, stroke, and limb ischemia. Antiphospholipid antibodies-particularly anticardiolipin antibodies and lupus anticoagulant-were frequently detected. A distinctive feature was the coexistence of aneurysmal lesions and thrombosis. Treatment generally included corticosteroids and cyclophosphamide, often combined with anticoagulation. Outcomes were heterogeneous, ranging from clinical improvement to severe complications, including amputations and death. Several reports also raised the possibility of catastrophic antiphospholipid syndrome (CAPS), further complicating the distinction between inflammatory multiorgan vasculitis and thrombotic microangiopathic disease. CONCLUSIONS: The association between PAN and APS represents a rare but clinically significant overlap syndrome characterized by the interplay between inflammatory vasculitis and thrombotic mechanisms. Recognition of this entity is essential, as it has important implications for diagnosis and management. Emerging evidence suggests that endothelial dysfunction, complement activation, NETosis, and thromboinflammatory pathways may contribute to the pathogenesis of this overlap phenotype. Future studies are needed to better define its pathogenesis, optimize therapeutic strategies, and improve outcomes.