Key diagnostic features of granulomatous interstitial nephritis due to Encephalitozoon cuniculi in a lung transplant recipient.

Microsporidia are increasingly recognized as opportunistic pathogens in immunocompromised organ transplant recipients (OTR). Disseminated infection due to Encephalitozoon sp. is reported mainly in human immunodeficiency virus (HIV)-positive patients and rarely in HIV-negative OTR. The clinical spectrum ranges from keratoconjunctivitis, to pneumonitis, to acute kidney injury. The kidney is a common site for disseminated infection; however, specialized techniques are required for definitive diagnosis. We report the first case of disseminated Encephalitozoon cuniculi infection in an HIV-negative lung transplant recipient diagnosed on renal biopsy. Five months after transplant, he presented with fever and a lung infiltrate and developed acute kidney injury. Renal biopsy showed granulomatous interstitial nephritis with gram-positive rod-shaped organisms with a "belt-like stripe" in tubular epithelial cells. Electron microscopy, polymerase chain reaction, and mammalian cell cultures of the urine sediment confirmed E. cuniculi infection. Retrospective review of a previous lung biopsy showed similar organisms. On the basis of electron microscopy findings, the patient was treated with albendazole, and immunosuppressive therapy was reduced. However, the patient expired due to Aspergillus pneumonia and disseminated E. cuniculi infection. Microsporidia should be considered in cases of fever of unknown origin and/or multiorgan infection in HIV-negative OTR when other causes have been excluded, as successful treatment requires early detection.