West Nile Virus Neuroinvasive Disease Presenting with Acquired Fanconi Syndrome, Which Resolved on Recovery.

Background: West Nile virus (WNV) is a mosquito-borne flavivirus that can cause neuroinvasive disease. Renal involvement is uncommon and acquired Fanconi syndrome has not been previously described in association with WNV. Case presentation: An 81-year-old male from Cyprus presented with fever, headache, disorientation, and signs of meningoencephalitis. Cerebrospinal fluid (CSF) analysis and neuroimaging supported the diagnosis of viral encephalitis. Extensive microbiological testing revealed WNV ribonucleic acid in urine and blood, but not in the CSF. The patient developed persistent hypokalaemia, metabolic acidosis, hypomagnesemia, and hypouricemia, with elevated fractional excretion of these solutes-findings consistent with Fanconi syndrome. Acyclovir was discontinued, and supportive treatment was provided. Renal function and electrolyte levels normalized by day 9. At 2-month follow-up, the patient had fully recovered with normal renal parameters. Conclusion: Renal complications of WNV are rarely documented and this case of WNV associated acquired Fanconi syndrome underscores the importance of evaluating kidney function and electrolyte status in WNV-infected patients. Early recognition of tubular dysfunction may prevent complications and improve outcomes. LEARNING POINTS: While renal complications of West Nile virus (WNV) are documented in rare cases, this is the first reported case of WNV-associated Fanconi syndrome.