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Diagnosis and Discussion: Case 1168

Final Diagnosis

Renal malakoplakia

Discussion

Malakoplakia, meaning “soft plaque” in Greek, is a rare chronic inflammatory condition that typically affects immunocompromised individuals, as seen in this case.1,2 Described by Michaelis, Gutmann and von Hansemann in the early 1900s, this granulomatous disease presents as soft plaque-like lesions, most commonly affecting the genitourinary tract, although involvement of other organ sites has been well documented.1-3 Most cases are associated with gram-negative infections, particularly Escherichia coli.1,2,4

Though poorly understood, pathogenesis is thought to be due to a bactericidal defect in macrophages leading to decreased clearance of bacteria. A deficiency in beta-glucuronidase and intracellular cGMP leads to inadequate microtubular function and lysosomal activity and subsequent incomplete elimination of bacteria from phagocytes.2 The pathognomonic Michaelis–Gutmann bodies, which appear as basophilic intracytoplasmic inclusions, represent calcified undigested bacterial elements, and can be highlighted with Prussian blue stain, von Kossa calcium stain, and periodic acid-Schiff stain.2–4  Histologic findings also include abundant histiocytes with small nuclei and granular acidophilic cytoplasm, termed von Hansemann cells, admixed with lymphocytes, plasma cells, and fibroblasts.2

The treatment of malakoplakia depends on disease extent. Bilateral or multifocal disease is commonly treated with antibiotics and may also include a cholinergic agonist to address lysosomal defects.2 Surgical excision is the preferred treatment for patients with unifocal disease, in which case complete resection is often curative.2,3 Nephrectomy may also be necessary in cases of extensive renal damage.2

References

  1. Stanton MJ, Maxted W. Malacoplakia: A Study of the literature and current concepts of pathogenesis, diagnosis and treatment. J Urol. 1981;125(2):139-146. doi:10.1016/S0022-5347(17)54940-X
  2. Purnell SDK, Davis B, Burch-Smith R, Coleman P. Renal malakoplakia mimicking a malignant renal carcinoma: a patient case with literature review. BMJ Case Rep. 2015;2015:bcr2014208652. doi:10.1136/bcr-2014-208652
  3. Wielenberg AJ, Demos TC, Rangachari B, Turk T. Malacoplakia presenting as a solitary renal Mass. Am J Roentgenol. 2004;183(6):1703-1705. doi:10.2214/ajr.183.6.01831703
  4. Bagnasco S, Gautam SC. Renal Malakoplakia. N Engl J Med. 2024;390(8):746-746. doi:10.1056/NEJMicm2301676