CD163+ Foamy Histiocytes in the Vitreous of a Patient with West Nile Virus-Associated Chorioretinitis

Purpose: Macrophages play a central role in the non-specific defense against viruses. We aim to report on the abundance of CD163+ foamy histiocytes in the vitreous humor of a patient with chorioretinitis secondary to West Nile Virus (WNV). Methods: Observational case report. Results: A 57-year-old diabetic woman with prior Hodgkin’s lymphoma presented with confusion, difficulty walking, and decreased vision in the right eye (RE). Visual acuity was 0.5 in the RE and 0.8 in the left eye (LE). Right relative afferent pupillary defect (RAPD) was elicited. Anterior segments were normal bilaterally. Vitreous cells and chorioretinal lesions were detected bilaterally. Few peripheral dot blot retinal hemorrhages and blurred optic disc margins were noted in RE. Diagnostic vitrectomy ruled out lymphoma. Cytokine analysis of the aqueous humor showed increased interleukin-6 (IL-6). Cytological examination of the vitreous revealed abundant foamy histiocytes with positive CD163 immunoreactivity. Serological tests confirmed acute WNV infection. Eventually, the patient developed RE optic disc pallor and an inferior scotoma. Conclusion: We present the first documented cytological evidence of CD163+ histiocytes in the vitreous humor in WNV-associated chorioretinitis. CD163+ macrophages participate in inflammation resolution, wound healing, and angiogenesis. We speculate that the CD163+ histiocytes in the vitreous may represent circulating CD163+ monocytes that have infiltrated the eye, as described in other viral infections such as HIV, as well as uveal resident macrophages activated in response to viral infection. While the clinical implications remain to be established, this observation may provide a basis for further investigation, particularly given that no approved vaccines or specific treatments for WNV currently exist.