Malacoplakia

Abstract

A case of malacoplakia of the bladder and intestinal tract is reported in which bacilliform organisms are demonstrated within the malacoplakic macrophages by light and electron microscopy. On electron microscopy, two types of cytoplasmic inclusions are found, those corresponding to the periodic acid Schiff-positive granules which are phagolysosomes, and the Michaelis-Gutmann bodies. Bacteria, probably coliforms, in various stages of degradation, are found within phagocytic vacuoles and phagolysosomes, sometimes in close apposition to phospholipid membranes. The Michaelis-Gutmann bodies develop within the phagolysosomes. It is postulated that the following sequence of events occurs in the pathogenesis of Michaelis-Gutmann bodies. Bacteria are phagocytosed by the malacoplakic macrophages, incorporated into phagolysosomes, and killed, but are incompletely digested. They persist as dense amorphous aggregates and phospholipid membranes which later become encrusted with calcium phosphate crystals to form the laminated Michaelis-Gutmann bodies. Why the macrophages respond in this unusual fashion to a common infectious organism is not clear. It may be due to an immunological abnormality affecting intracellular digestion. Other factors, such as infection with an unusual strain of coliform or intrinsically abnormal macrophages, are discussed. The world literature of intestinal malacoplakia is reviewed and the aggressive nature of intestinal involvement is stressed.