Malakoplakia in the Urinary Bladder of 4 Puppies

Abstract

Malakoplakia in humans most often affects the urinary bladder and is characterized by inflammation with von Hansemann-type macrophages, with or without Michaelis-Gutmann bodies, and is frequently associated with Escherichia coli infection. We describe the microscopic features of malakoplakia in the urinary bladder of 4 puppies. In all cases, the lamina propria of the urinary bladder was markedly expanded by sheets of large, round to polygonal macrophages with intracytoplasmic, periodic acid-Schiff-positive granules and granular inclusions, and rare Prussian blue-positive inclusions. Macrophages were positive for CD18 and Iba1. In 2 cases, Michaelis-Gutmann bodies were detected with hematoxylin and eosin stain and were best demonstrated with von Kossa stain. E. coli infection was confirmed in 2 cases with bacterial culture or polymerase chain reaction (PCR) and sequencing of the bacterial 16S ribosomal RNA gene. Transmission electron microscopy of one case demonstrated macrophages with abundant lysosomes, phagolysosomes, and rod-shaped bacteria. Microscopic features were similar to human cases of malakoplakia. In dogs, the light microscopic characteristics of malakoplakia closely resemble granular cell tumors and histiocytic ulcerative colitis.

Keywords: Michaelis-Gutmann bodies; dog; granulomatous; macrophage; malakoplakia; urinary bladder.

Figures 1–5.

Malakoplakia, urinary bladder, dogs. Figure 1. Case 1, formalin-fixed. The mucosa is markedly thickened and has a nodular surface. Figure 2. Case 1. The lamina propria (double arrow) is markedly expanded by cellular infiltrates. The urothelium is mildly hyperplastic. Hematoxylin and eosin (HE). Figure 3. Case 3. The cellular infiltrate consists of sheets of large, round to polygonal macrophages with abundant eosinophilic granular cytoplasm and round eosinophilic granular inclusions (arrowheads). HE. Figure 4. Case 2. Macrophages and mixed leukocytes express CD18. Scattered leukocytes infiltrate between urothelial cells. Immunohistochemistry (IHC) for CD18. Figure 5. Case 2. Macrophages express Iba1. IHC for Iba1.

Figures 6–11.

Malakoplakia, urinary bladder, dogs. Figure 6. Case 3. Macrophage cytoplasmic granules and inclusions are intensely periodic-acid Schiff (PAS)–positive. PAS. Figure 7. Case 2. Multiple macrophages contain dark blue cytoplasmic rod-shaped bacteria. Giemsa. Figure 8. Case 4. Within the inner tunica muscularis are multiple Michaelis-Gutmann (MG) bodies (arrowheads). Inset: A MG body is in the cytoplasm of a macrophage. HE. Figure 9. Case 4. Macrophages contain numerous black-staining cytoplasmic inclusions (mineral). Von Kossa. Figure 10. Case 1. Macrophages contain rare blue cytoplasmic inclusions. Prussian blue. Figure 11. Case 1. A macrophage has a large phagolysosome (asterisk) containing multiple rod-shaped bacteria (arrowheads). The nucleus (N) is peripheralized. Bar = 1 μm. Transmission electron microscopy