Renal thrombotic microangiopathy revisited: when a lesion is not a clinical finding

Despite advances in the field of thrombotic microangiopathy (TMA) and associated syndromes such as thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS), they still leave several issues unresolved. For instance, actual diagnostic criteria on which therapeutic decisions rely are relatively narrow and focused on TTP-HUS, with the consequence that non-idiopathic and atypically-presenting TMA are overlooked. In addition, nosologic classifications of TMA disorders have varied substantially over the years, but are still devised from historical rather than mechanistic data. As such, it is perhaps not surprising that even today TMA is erroneously used as an interchangeable term with TTP-HUS, and missed or inappropriately diagnosed on various occasions. Yet, recognizing TMA is of crucial importance given that this lesion often manifests with potentially reversible renal failure. In this editorial, which is presented from a Nephrologist's perspective, we propose that TMA disorders need to be reclassified to include most types of presentations and confirmed or excluded through more elaborate diagnostic approaches.