Thrombotic thrombocytopenic purpura associated with polyarteritis nodosa

We present a case of classical polyarteritis nodosa (PN) overlapping thrombotic thrombocytopenic purpura (TTP). A 70-year-old woman was transferred to our hospital because of general fatigue and fever. On admission, laboratory findings revealed leukocytosis, normochromic normocytic anemia and renal dysfunction. About one week later, she developed disturbance of consciousness, and laboratory findings revealed rapidly progressive thrombocytopenia and renal dysfunction. We suspected the presence of microscopic polyangiitis (MPA), based on mild elevation of myeloperoxidase (MPO) anti-neutrophil cytoplasmic antibody (ANCA). On post-admission Day 11, renal biopsy was performed but the diagnosis of MPA could not be confirmed because of the absence of glomerular crescent formation or vasculitis. However, the biopsy specimen showed many collapsed glomeruli and interstitial inflammation, indicating the presence of occlusive lesions, such as vasculitis in larger arteries. We instituted methylprednisolone pulse therapy, cyclophosphamide and plasma exchange, because the clinical symptoms also satisfied the criteria of TTP. Despite the intensive treatment, the patient died on 43rd day of hospitalization due to thalamic hemorrhage. Autopsy showed typical findings of classical PN including disruption of arterial walls and fibrinoid necrosis in the medium-sized arteries of the kidneys and colon. We detected reduced activity of von Willebrand factor-cleaving protease (VWF-CP) and the presence of plasma inhibitory IgG against VWF-CP. A better understanding of the mechanisms would be useful.