Sickle Cell Anemia (SS)



Renal damage occurs in almost all patients homozygous for this hereditary disease, but SS is a most unusual cause of renal failure. The primary injury occurs in the renal medulla, where frequent vascular occlusion from erythrocyte sickling in the hypertonic medullary environment causes ob­literation of vasa recta. Hematuria and a reduction in urinary concentrating ability are prominent manifestations of this phenomenon.

Hematuria, usually in the microscopic range, occurs in most SS patients, but dramatic and pro­longed bouts of gross hematuria may be seen. He-maturic patients with sickle hemoglobin are most often heterozygotes. This is due simply to the greater number of patients with SS trait. Bleeding originates in the left kidney in most cases. Bed rest, forced hydration, and transfusions are the standard treatment for gross hematuria; nephrec­tomy is rarely indicated.

A decreased concentrating ability is a very com­mon defect in SS but is not usually of a magnitude sufficient to cause clinically apparent polyuria. Since these patients dilute urine normally, the de­fect is likely caused by a failure to maintain med­ullary hypertonicity due to an alteration in med­ullary blood flow. The pathology of SS is that of vasa recta obliteration with medullary interstitial edema and fibrosis. There is a pronounced ten­dency for papillary necrosis to occur.