Relapse of thrombotic thrombocytopenic purpura: is it a continuum of disease?

The recurrence of thrombotic thrombocytopenic purpura (TTP) in 20 to 50% of patients who survive their initial episode, is not only a challenge to manage clinically, but brings to light our lack of understanding of the underlying pathophysiology. Recurrence may occur close to apparent hematologic remission or remotely, months later. Given that surveillance of TTP relies on surrogate measures such as hematologic recovery, normalization of serum lactate dehydrogenase (LDH) and resolution of clinical signs, it is plausible that some recurrences are actually a continuum of disease. Standardizing definitions for remission, exacerbation, and relapse are important for consistency of patient management and interpreting the medical literature. When TTP recurs, several adjuncts to therapeutic plasma exchange (TPE) have been used, including splenectomy, vincristine, and rituximab. Although it would seem intuitive that more severe disease would predict a greater likelihood of relapse, the degree of thrombocytopenia at presentation, the persistence of schistocytosis at discontinuation of TPE, the elevation of LDH, and the length of time to attain clinical remission are not reliable indicators of the clinical outcome of any individual TTP patient. Measurement of ADAMTS13 activity and its inhibitor offer new promise for prognostic and pathophysiologic significance; however, more extensive scientific investigation is needed.