The antiphospholipid syndrome is an autoimmune and multisystem disorder of recurrent thrombosis, pregnancy loss, and thrombocytopenia associated with the presence of antiphospholipid antibodies, persistently positive anticardiolipin antibodies, anti–β2-glycoprotein I antibodies, or antilupus anticoagulant (Table 4).15,16 Of 5 patients in the present case series, 4 had positive antiphospholipid antibodies. Based on the latest revised classification criteria for antiphospholipid syndrome, none of these patients fulfilled the clinical or laboratory criteria for definite antiphospholipid syndrome.16 Histologic findings in antiphospholipid syndrome are those of thrombosis without significant evidence of inflammation in the vessel wall (Table 5).16,17 In the biopsy specimens of all the present patients, there was a dense mononuclear infiltrate in the deep dermal arterioles, a feature not consistent with vasculopathy primarily due to the antiphospholipid syndrome. Antiphospholipid antibodies have also been positive for disease in a variety of primary systemic vasculitides, including Wegener granulomatosis, giant cell arteritis, polyarteritis nodosa, and Churg-Strauss syndrome.18- 22 In a recent study,23 17% of patients with primary systemic vasculitis had positive anticardiolipin antibodies or lupus anticoagulant on at least 1 occasion. It has been suggested that anticardiolipin antibodies present in these situations were an epiphenomenon of exposed endothelial cells and did not have prothrombotic properties.18,19 This could explain why 2 of the present patients who initially tested negative for antiphospholipids had low positive titers on repeated testing months later. The pathogenicity of the antibodies may also be affected by host genetic factors, antibody isotype, and vessel wall integrity.22 In the presence of anticardiolipin or anti–β2-glycoprotein I antibodies, a vasculitis or mutation in thrombophilic genes may be the “second or third hit” necessary for the generation of thrombosis in patients with the antiphospholipid syndrome.24 It is unclear what role antiphospholipid antibodies play in the pathogenesis of lymphocytic thrombophilic arteritis. However, the low levels of antiphospholipid antibodies, the lack of significant systemic involvement, the absence of evidence of macrovascular thrombosis, the absence of antiphospholipid antibodies in 1 patient, and the presence of a prominent lymphocytic component are points against antiphospholipid antibodies contributing significantly to the pathogenicity of this condition.