Cryptosporidium Diarrhea in a Patient With Class IV Lupus Nephritis on Cyclophosphamide: An Underreported Case.

is a protozoan parasite that typically causes self-limited diarrhea in healthy individuals but can result in prolonged, severe illness in those who are immunocompromised. While this infection is well recognized in HIV-positive patients, it is less frequently reported in individuals with lupus nephritis on immunosuppressive therapy. We report the case of a 27-year-old man with biopsy-confirmed class IV lupus nephritis who was receiving cyclophosphamide and corticosteroids. He was admitted with generalized edema, ascites, and declining kidney function. On hospital day 6, he developed acute-onset watery diarrhea. Stool microscopy identified , and he was treated with nitazoxanide and rifaximin, resulting in improvement of his diarrhea. His hospital stay was complicated by the development of left-sided parotitis with abscess formation, bilateral pleural effusions, worsening renal failure requiring hemodialysis, and interstitial lung changes. He was discharged with symptomatic improvement but was later readmitted elsewhere, received additional cyclophosphamide, and ultimately died from septic shock and multi-organ failure. This case highlights the need for heightened clinical suspicion for opportunistic infections, such as cryptosporidiosis, in patients with lupus nephritis who present with new-onset diarrhea, particularly when on potent immunosuppression. It also reflects the broader challenges in managing such patients, where balancing immunosuppressive treatment against infection risk is both complex and critical.