The first human case of malakoplakia was described by von Hansemann, who coined the term 'malakoplakia' [1
]. The aetiology of this condition is probably inflammatory. This benign non-neoplastic condition is believed to result from inadequate killing of bacteria, most commonly Escherichia coli, by a defect in monocytes and macrophages phagolysosomal activity. This response can also be seen with mycobacterial and fungal infections in immunocompromised patients. More than one organ can be affected simultaneously.
Clinically and macroscopically malakoplakia can simulate tumours or abscesses. Histologically sheets and aggregates of histiocytes (von Hansemann cells) with fine eosinophilic granular cytoplasm are seen on haematoxylin and eosin stain. They are characterised by intracellular and extracellular, round basophilic concretions, called the Michaelis-Gutmann (MG) bodies. These stain with PAS diastase, von Kossa stain and Perls' Prussian blue. Electron microscopically, MG bodies show concentric crystalline laminations with a dense central zone containing partially digested bacteria and a thin outer zone. Immunohistochemically the cells are positive with CD68, lysozyme and α-chymotrypsin.
Blackshear first reported Malakoplakia in the appendix in 1970 in a case of pulmonary nocardiosis [2
]. Since then four more cases of malakoplakia of the appendix have been reported [3
]. This includes an intriguing case of malakoplakia of the appendix associated with the eggs of Taenia species [5
Although gastrointestinal malakoplakia is associated with a variety of conditions including ulcerative colitis, tuberculosis, diverticular disease, adenomas and carcinomas, these conditions have not been described with malakoplakia of the appendix. Histologically malakoplakia in the gastrointestinal tract (GIT) must be differentiated from Whipple's disease, other infectious and noninfectious granulomatous disorders and histiocyte storage diseases. The most common location for malakoplakia in the GIT is the colon and this is most commonly associated with carcinoma [6
The exact aetiology of malakoplakia is ill understood. Malakoplakia is diagnosed primarily on histological grounds. Irrespective of the site, all malakoplakias share the same morphological features. Gram-negative bacteria, most commonly E. coli, have been frequently isolated from the cases of genitourinary malakoplakia. Various organisms that have been associated with this condition include E. coli, Mycobacterium tuberculosis, Shigella boydii, Paracoccidioides species, Rhodococcus equi, Yersinia enterocolitica, Klebsiella pneumoniae, Proteus mirabilis, Staphylococcus aureus, Pseudomonas aeruginosa, Enterobacter aerogenes and Taenia species [5
]. The initial event in the pathogenesis of malakoplakia is partial digestion of the offending organism in macrophages by phagolysosomes. These are eventually damaged, resulting in calcification [7
]. Some studies suggest that the underlying defect is a 3',5'-guanosine monophosphate dehydrogenase deficiency, causing diminished phagolysosomal and bactericidal activity.
Immunosuppressive conditions have been linked with malakoplakia. A case of ulcerative colitis treated with proctocolectomy showed immunoglobulins and muramidase within the malakoplakia histiocytes and an unusually high E. coli serum antibody titre [9
Multiple blocks from the small and large intestine in our case failed to show malakoplakia that was just limited to the appendix and showed no other changes. The colon showed a reduced amount of mucosa associated lymphoid tissue (MALT) and extensive active inflammation and we propose that this may have led to the local immunosuppression, which allowed the organisms to be inefficiently cleared and proliferated. The patient's symptoms in our case were attributable to ulcerative colitis and not to malakoplakia, which was an incidental finding. No pre-operative clinical or radiological evidence of malakoplakia was found and the condition was diagnosed incidentally at histopathology. The underlying disease in our case was ulcerative colitis and the malakoplakia was limited to the appendix. The significance of this finding is not clear but we feel that this was a localised manifestation of the underlying immunosuppressive state. Ulcerative colitis and treatment with steroids may make a patient immunosuppressive and the local and systemic change in the immunity may facilitate the proliferation of the organisms and modify the phagocytic abilities of the macrophages.