A 52-year-old woman with recurrent fever of unknown origin: a case report

Abstract Background Recurrent fever of unknown origin (FUO) poses a significant diagnostic challenge. While nutritional deficiencies, particularly of vitamin D, are recognized for their immunomodulatory roles, their potential as a plausible contributing factor of recurrent fever remains underappreciated. This case report aims to describe the resolution of recurrent fever after vitamin D repletion. Case presentation A 52-year-old woman presented with a one-month history of recurrent high-grade fever (peak 39.4 °C), leukopenia, anemia, and systemic symptoms. An exhaustive diagnostic workup was performed to exclude infectious, autoimmune, and neoplastic etiologies. Comprehensive investigations, including metagenomic sequencing of cerebrospinal fluid, ruled out common FUO etiologies. A subsequent nutritional assessment revealed the underlying cause——severe vitamin D deficiency (25-hydroxyvitamin D: 8.7 nmol/L, equivalent to 3.48 ng/mL), attributed to insufficient sun exposure. Upon initiation of oral vitamin D supplementation, the patient’s fever resolved entirely. No recurrence was observed during an 18-month follow-up period, coinciding with the normalization of her vitamin D levels. Conclusions This case identifies severe vitamin D deficiency as an underrecognized potential contributing factor of recurrent fever. It underscores the critical importance of integrating nutritional assessment, specifically vitamin D status evaluation, into the standard diagnostic algorithm for FUO. This approach may contribute to targeted treatment and should be considered as a complementary component of the comprehensive FUO diagnostic workup.