Bilateral Herpetic Keratitis following Cladribine Immunosuppression: A Case Report.

Introduction: Disease-modifying therapies for multiple sclerosis (MS), including cladribine, alter immune function and may increase susceptibility to viral reactivation. While herpesvirus infections have been reported with cladribine, herpetic keratitis has not been previously described. We report a case of bilateral recurrent micro-dendritic keratitis following cladribine therapy in a patient with relapsing-remitting MS (RRMS). Case Presentation: A 60-year-old male with RRMS developed progressive leukopenia after completing two cycles of cladribine. Four months after treatment, he presented with decreased vision OD and was found to have a dendritic corneal lesion consistent with herpetic keratitis, confirmed by positive herpesvirus PCR. Despite antiviral therapy, he developed sequential involvement of the left eye and recurrent bilateral episodes characterized by multiple, micro-dendritic lesions, stromal haze, ocular discomfort, and photophobia. Visual acuity declined during flares but improved with oral valacyclovir and ganciclovir gel drops. At peak severity, multiple Thygeson-like lesions with underlying stromal inflammation were present in both eyes. With continued therapy, visual acuity recovered to 20/20 bilaterally, though the disease course fluctuated over several months. Conclusion: This case demonstrates a rare presentation of bilateral, recurrent micro-dendritic herpetic keratitis in the setting of cladribine-induced immunosuppression. The temporal relationship between lymphocyte depletion and symptom onset suggests impaired cell-mediated immunity as a contributing factor. Clinicians should consider atypical herpetic ocular disease in immunosuppressed patients and may need prolonged antiviral therapy and close monitoring to reduce recurrence and preserve vision.