Thrombotic thrombocytopenic purpura misdiagnosed as autoimmune cytopenia: Causes of diagnostic errors and consequence on outcome. Experience of the French thrombotic microangiopathies reference centre

Thrombotic thrombocytopenic purpura (TTP) has a devastating prognosis without adapted management. Sources of misdiagnosis need to be identified to avoid delayed treatment. We studied 84 patients with a final diagnosis of severe (<10%) acquired ADAMTS13 deficiency-associated TTP from our National database that included 423 patients, who had an initial misdiagnosis (20% of all TTP). Main diagnostic errors were attributed to autoimmune thrombocytopenia, associated (51%) or not (37%) with autoimmune hemolytic anemia. At admission, misdiagnosed patients were more frequently females (P=.034) with a history of autoimmune disorder (P=.017) and had organ involvement in 67% of cases; they had more frequently antinuclear antibodies (P=.035), a low/undetectable schistocyte count (P=.001), a less profound anemia (P=.008), and a positive direct antiglobulin test (DAT) (P=.008). In multivariate analysis, female gender (P=.022), hemoglobin level (P=.028), a positive DAT (P=.004), and a low schistocytes count on diagnosis (P<.001) were retained as risk factors of misdiagnosis. Platelet count recovery was significantly longer in the misdiagnosed group (P=.041) without consequence on mortality, exacerbation and relapse. However, patients in the misdiagnosed group had a less severe disease than those in the accurately diagnosed group, as evidenced by less organ involvement at TTP diagnosis (P=.006). TTP is frequently misdiagnosed with autoimmune cytopenias. A low schistocyte count and a positive DAT should not systematically rule out TTP, especially when associated with organ failure.