A Diagnostic Odyssey: Successfully Treated Cytomegalovirus-Induced Immunodeficiency with Tuberculosis Coinfection Presenting as Fever of Unknown Origin in a Young Male

Background: Fever of unknown origin (FUO) in tuberculosis-endemic regions presents a significant diagnostic challenge. This complexity is heightened when concurrent infections and immune dysregulation, such as that caused by cytomegalovirus (CMV), confound the clinical picture and mimic other immunodeficiency states. Case Presentation: A previously healthy 20-year-old Filipino male presented with a three-week history of intermittent fever, malaise, and left cervical lymphadenopathy. An extensive workup for common infectious, autoimmune and malignant causes was unrevealing. However, laboratory testing revealed CMV viremia (463 copies/mL) with CD4⁺ T cell lymphopenia (332 cells/μL), despite a negative HIV evaluation. An excisional lymph node biopsy confirmed rifampicin-sensitive Mycobacterium tuberculosis, while bacterial culture also yielded Enterobacter cloacae. The patient received sequential antibacterials, then two weeks of valganciclovir—resulting in CMV clearance (undetectable viral load) and CD4⁺ T cell recovery (661 cells/μL). A follow-up examination four months later confirmed sustained CMV clearance and normal CD4⁺ T cell count (695 cells/μL). Anti-tuberculosis therapy, complicated by a drug-induced rash but successfully rechallenged, was completed with excellent tolerance and full clinical recovery. Conclusion: This case illustrates the diagnostic complexity of FUO in endemic areas, highlighting how CMV-induced immunosuppression, even in immunocompetent individuals, can mimic HIV infection and predispose to opportunistic coinfection. Careful evaluation and thorough infectious workup were pivotal in achieving diagnostic clarity and therapeutic success.