Human T-lymphotropic Virus Type 1 (HTLV-1)-Associated Uveitis Presenting With Frosted Retinal Vasculitis

Retinal vasculitis is a manifestation observed in various forms of uveitis. However, frosted retinal vasculitis, a severe type of retinal vasculitis, is seen in only a limited number of cases, typically associated with severe infections or autoimmune inflammatory conditions. A 65-year-old woman presented to our hospital after noticing a decline in vision in both eyes over the preceding month. Examination revealed vitritis and frosted retinal vasculitis in both eyes. Fluorescein angiography showed marked leakage from the optic disc and retinal vessels. Optical coherence tomography (OCT) revealed a serous retinal detachment at the right fovea. Sarcoidosis and Behçet's disease were ruled out based on blood tests, chest computed tomography (CT) scans, and the absence of extraocular symptoms or findings. There were no abnormalities in the white blood cell count or differential, and no elevation of C-reactive protein (CRP) was observed. While infections caused by various bacteria, viruses, and Toxoplasma were ruled out, elevated anti-human T-lymphotropic virus type 1 (HTLV-1) antibodies were detected. Based on these findings, the patient was diagnosed with HTLV-1-associated uveitis, and oral prednisolone therapy was initiated at a dosage of 30 mg. The vasculitis improved dramatically, and the dosage was gradually tapered while the condition remained stable. However, 16 months after the initial visit, the vasculitis worsened, necessitating an increase in the prednisolone dosage back to 30 mg. Subsequently, the dosage was tapered again, and treatment was discontinued 27 months after this resumption (43 months after the initial start of prednisolone). There was no recurrence of vasculitis thereafter, and the affected vascular areas transformed into degenerative lesions. Thus, HTLV-1-associated uveitis should be considered as a potential underlying cause of frosted retinal vasculitis.