Thrombotic microangiopathy and the kidney: a nephropathologist's perspective

Thrombotic microangiopathy is a common renal pathologic finding, which is characterized by the presence of endothelial cell injury and microvascular thrombi. The spectrum of clinical diseases that are connected by a thrombotic microangiopathic injury may appear to be unrelated, but overactivation of the complement system is emerging as an important mechanism, especially in atypical haemolytic uraemic syndrome, anti-phospholipid antibody syndrome, HELLP syndrome, and others. Although few pathologic findings enable the pathologist to establish the precise aetiology of the microvascular injury, kidney biopsy remains the gold standard for diagnosing renal thrombotic microangiopathy and excluding other potential causes of kidney injury. After this critical step, additional investigation of the clinical and laboratory data is necessary to establish the underlying aetiology and guide subsequent therapeutic options. The salient clinical and pathologic features of common diseases that are associated with thrombotic microangiopathy will be discussed.