1660 Malakoplakia of the Rectum Masquerading as a Tumor: A Case Report

Abstract

INTRODUCTION: Malakoplakia is a rare inflammatory disorder that occurs in the clinical setting of persistent infections, immunosuppression and tumors. The most common sites of involvement are the urinary, gastrointestinal and respiratory tracts, skin, brain and lymph nodes where they can mimic malignancies. CASE DESCRIPTION/METHODS: A 60-year-old woman with myasthenia gravis and stage IV metastatic thymoma (status-post resection and chemo-radiation) presented with persistent weight loss, bloating, nausea, tenesmus and hematochezia. Her recent history included treatment-resistant Giardia lambia infection for one year as well as recently diagnosed Norovirus and Enteroaggregative Escherichia coli, diagnosed by stool pathogen PCR testing. On colonoscopy, the rectum contained a 7 cm region of polypoid, non-circumferential, non-obstructing nodules (Figure 1) which were highly suspicious for tumor. Microscopically, biopsies revealed rectal lamina propria infiltration by epithelioid cells with small central nuclei, eosinophilic cytoplasm (Figure 2) and lamellated cytoplasmic calcifications (Figure 3). The cells expressed cytoplasmic CD68 (Figure 2) and Von Kossa stain highlighted the calcifications, consistent with Michaelis-Gutmann bodies (Figure 3). Immunostain for pancytokeratin and Ziehl-Neelsen and Gomori's methenamine silver stains were negative. The final diagnosis was malakoplakia. A re-biopsy of the lesion showed positivity for Cytomegalovirus (CMV) immunostain and high levels of CMV viremia (1010IU/mL), for which she was treated with Gancyclovir. DISCUSSION: Malakoplakia is a rare gastrointestinal disorder without specific symptoms, endoscopic features or gross findings and tends to masquerade as a tumor. As illustrated herein, it is often an unexpected diagnosis that depends on pathological recognition of characteristic microscopic features. The correct diagnosis is critical to avoid inappropriate radical treatment. Various micro-organisms have been implicated in its development including bacteria, most commonly E. coli, viruses, fungi and even protozoa such as Taeniaspecies and it is characterized by defective bactericidal activity of the macrophages. Pathologists should be aware that malakoplakia can coexist with malignancy and tuberculosis, therefore, thorough sampling of mass lesions and appropriate adjunctive stains are advisable. Risk factors in our case included an immunocompromised state, multiple concurrent infections, and advanced malignancy, although no malignancy was identified in the biopsies.