Renal malacoplakia reappraised.

Renal malacoplakia is an unusual form of chronic tubulointerstitial nephritis with a predilection for patients with recurrent urinary tract infections and an immunocompromised state. Its characteristic feature is the parenchymal infiltration by macrophages with ample cytoplasm containing abundant periodic acid-Schiff-positive granules, known as von Hansemann cells, and the presence of diagnostic extracytoplasmic or intracytoplasmic calcospherites, known as Michaelis-Gutmann bodies. Renal malacoplakia is more common in women (female to male ratio 3:1), in whom the lesions develop in a younger age group (third to fifth decade) than in men (over 50 years). Enlarged kidneys in the presence of persistent urinary infection should lead to the consideration of this entity. The diagnosis can only be established by pathologic examination of renal tissue. Renal biopsy early in the course of the disease is essential since in an increasing number of cases medical therapy has resulted in resolution of the disease process and preservation of renal function.