Renal malakoplakia mimicking a complicated renal cyst infection and abscess invading psoas muscles: a case report

Malakoplakia is a chronic granulomatous disease resulting from defective macrophage function. It affects any organ and frequently involves the urinary bladder and skin, particularly in immunocompromised patients. Owing to its rarity and the presence of space-occupying lesions, renal malakoplakia presents a significant challenge in diagnosis, as it is often mistaken for malignancies or abscesses. Here, we report a rare case of renal malakoplakia mimicking a complicated renal cyst infection and abscess in a 77-year-old Korean man. The patient initially presented with a 6-day fever and was treated for a presumed complicated renal cyst infection and psoas muscle abscess. Despite antibiotic therapy, the lesions persisted and continued to increase in size. Percutaneous needle biopsy revealed atypical inflammation with abscess formation, and pathological von Kossa staining confirmed the diagnosis of malakoplakia. The patient was successfully treated with oral trimethoprim/sulfamethoxazole, which resulted in lesion reduction and clinical improvement. This case report highlights the importance of considering malakoplakia in the differential diagnosis of renal infections with space-occupying lesions and emphasizes the significance of timely diagnosis and appropriate treatment.