Correct!
4. Malakoplakia
The histopathologic features do not indicate the presence of malignancy, either related to bronchogenic carcinoma or a lymphoproliferative disorder. Histopathological features of sclerosing pneumocytoma include surface and round cells, the latter with abundant eosinophilic cytoplasm with indistinct cell borders and nucleoli, oval nuclei, possibly even chromatin, and indistinct nucleoli; vacuolization, hyperchromasia, pleomorphism may be present. A sclerotic stroma may be seen. However, none of these features were mentioned in the biopsy specimen, making sclerosing pneumocytoma an unlikely diagnosis. Furthermore, sclerosing pneumocytoma- a benign neoplasm- would be expected to grow slowly, rather than the rapid interval enlargement seen with this lesion. No evidence of fungal hyphae to suggest Aspergillus infection was seen after biopsy; rather bacteria were recovered. Michaelis-Gutmann bodies were present histopathologically in the biopsy specimen; these structures represent concentrically layered basophilic inclusions, thought to reflect the remains of incompletely digested bacterial remnants that have undergone mineralized by calcium or iron. While most commonly encountered in the urinary tract, Michaelis-Gutmann bodies are typical of malakoplakia.
Clinical Course: The patient had been started on ciprofloxacin, but her Escherichia coli urinary tract infection was found to be resistant to this drug and she was switched to Augmentin. She completed this therapy and chest CT was repeated 4 months after diagnosis (Figure 7), showing that the nodule had decreased in size from its largest measurement of 20 mm to 12 mm.
Figure 7: Unenhanced chest CT performed 4 months after the diagnosis of malakoplakia was made and following prolonged antibiotic therapy shows decreased size of the left upper lobe nodule, now 12 mm, previously 20 mm.
One year after diagnosis the patient is doing well.
Diagnosis: Malakoplakia presenting as a growing solitary pulmonary nodule
Discussion: Malakoplakia is a rare, often chronic, multisystem granulomatous inflammatory condition that typically presents as single or multiple soft plaques affecting various organs, most commonly the genitourinary system. The mean age of diagnosis is approximately 50 years, although malakoplakia may present at any age. While whites are more commonly affected than other races, sources differ regarding the sex predilection of malakoplakia. A history of immunosuppression, such as diabetes mellitus, malignancy, organ transplantation, alcoholism, lymphoproliferative disorder, or chronic corticosteroid therapy is a common predisposing factor.
Although the urinary tract is the most commonly affected site, malakoplakia has been reported in a number of other organ systems, such as the gastrointestinal tract, skin, neck, lungs, and central nervous system. When presenting in the urinary tract, patients often complain of dysuria, hesitancy, and urgency, often in the context of a urinary tract infection. The presentation of malakoplakia in other organ systems results in symptoms referable to those systems, with a pulmonary presentation typically manifesting as one or more pulmonary nodules that may be detected asymptomatically.
The pathogenesis of malakoplakia is thought to be related to a defective response to bacterial infection, particularly impaired phagolysosomal activity by monocytes and macrophages- these cells are able to ingest bacteria but cannot digest them, and the partially digested bacteria accumulate in the cytoplasm of phagocytic cells, leading to an immune-mediated granulomatous response. The residual bacterial glycolipid provides a substrate for iron and calcium deposition within the phagocytic cells, leading to the formation of the histopathologically pathognomonic feature of malakoplakia- the basophilic inclusion body known as the Michaelis-Gutmann body. The most commonly associated infection in patients with malakoplakia is Escherichia coli; Klebsiella and Proteus species are less commonly associated.
Treatment of malakoplakia may consist of surgical resection for amenable lesions, particularly when the presentation of the disorder resembles malignancy. Antibiotic therapy directed at Escherichia coli is commonly employed. Reduction in immunosuppression may be required induce malakoplakia regression.
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