&p.1:Abstract We describe the occurrence of renal Encepha- litozoon (Septata) intestinalis infection in a 35-year-old AIDS patient who died with disseminated tuberculosis. The patient did not complain of specific symptoms in- volving the kidney or lower urinary tract during life, but at autopsy, light microscopic examination of the kidney revealed numerous small round or oval bodies in the tu- bules and tubular cell cytoplasm that were interpreted as intracellular protozoa. Transmission electron microscopy of tissue retrieved from paraffin-embedded samples iden- tified these organisms as microsporidia belonging to the Encephalitozoonidae family, but did not allow definitive identification of the species of infecting parasite. This was made possible only by means of Southern blot hy- bridization after the polymerase chain reaction, which recognized the micro-organism as E. intestinalis. &kwd:Key words AIDS · Microsporidium · Kidney · Transmission electron microscopy · Polymerase chain reaction&bdy: Introduction Microsporidia are obligate intracellular spore-forming protozoan parasites causing intestinal (Enterocytozoon bi- eneusi and Encephalitozoon (Septata) intestinalis and dis- seminated (E. hellem, E. cuniculi and E. intestinalis) in- fections, which are being reported with increasing fre- quency in patients with AIDS [5, 8, 9, 11]. Because of the small size of micro-organisms and spores, diagnosis by means of light microscopical examination of biopsy and cytology specimens may be difficult when routine histo- chemical stains are used, although modified Gram, War- thin-Starry and fluorescent chitin stains have made diag- nosis considerably easier [12, 14]. Diagnosis at autopsy is even more challenging, because of the presence of post- mortem tissue artifacts. Microsporidia infections are therefore undoubtedly underdiagnosed, especially in clin- ically unsuspected cases. Furthermore, their morphologi- cal speciation is a problem in autopsy specimens even when transmission electron microscopy (TEM) is used, because, as in the case of well-preserved biopsy material, all the Encephalitozoa have the same appearance with the exception of E. intestinalis, which can be identified by its unique honeycombed parasitophorous vacuole. We report an autopsy case of renal E. intestinalis in- fection in a symptom-free AIDS patient. The uncertain histological diagnosis was supported by means of TEM and DNA polymerase chain reaction (PCR) investigation Clinical history A 35-year-old, HIV-positive, male intravenous drug user was ad- mitted to the “Ospedale Maggiore della Carità”, Novara, in No- vember 1993 because of cervical lymphadenopathy. The results of the laboratory tests were unremarkable with the exception of the CD4 count (180 cells/ml), serum alaninaminotransferase (ALT; 89 U/ml) and aspartatoaminotransferase (AST; 42 U/ml). The lymph node biopsy revealed tuberculous lymphadenitis and the patient was discharged after specific therapy. In January 1995, the patient was hospitalized again following the onset of fever and lethargy. Laboratory tests revealed hypo- natraemia (Na+ 120 mEq/l). His renal function was normal (blood R. Boldorini ( ✉ ) 1 · G. Monga Dipartimento di Scienze Mediche, Facoltà di Medicina e Chirurgia di Novara, Novara, Italy A. Tosoni · M. Nebuloni · G. Costanzi V Cattedra di Anatomia Patologica, Istituto di Scienze Mediche L“Sacco”, Università di Milano, Milano, Italy E.S. Didier Department of Microbiology, Tulane Regional Primate Research Center, Covington, La., USA G. Mazzucco Dipartimento di Scienze Mediche ed Oncologia Umana, Torino J.M. Orenstein Department of Pathology, George Washington University Medical Center, Washington, D.C., USA Mailing address: 1 Servizio di Anatomia Patologica, Ospedale Maggiore della Carità, Corso Mazzini 18, I-28100 Novara, Italy, Tel.: +39-321-373594, Fax: +39-321-373485&/fn-block: Virchows Arch (1998) 432:535–539 © Springer-Verlag 1998 ORIGINAL ARTICLE &roles:Renzo Boldorini · Guido Monga · Antonella Tosoni Elizabeth S. Didier · Manuela Nebuloni Giulio Costanzi · Gianna Mazzucco · Jan M. Orenstein Renal Encephalitozoon (Septata) intestinalis infection in a patient with AIDS Post-mortem identification by means of transmission electron microscopy and PCR &misc:Received: 8 September 1997 / Accepted: 1 December 1997