ABCA4-associated retinopathy complicated by didanosine-associated retinal toxicity.

Purpose: To describe a rare case of severe central and peripheral chorioretinal atrophy in a patient with ABCA4-associated retinopathy and prior didanosine exposure. Observations: A 66-year-old man with a 20-year history of Stargardt disease and HIV/AIDS treated with didanosine for almost ten years in the late '90s presented with progressive bilateral visual loss and color desaturation. Best-corrected visual acuity was 20/400 in both eyes. Multimodal imaging revealed extensive retinal pigment epithelium and choroidal atrophy involving both the macula and mid-periphery, with macular thinning and structural damage confirmed on optical coherence tomography. The peripheral atrophy pattern was consistent with known didanosine toxicity, while the macular degeneration was typical of ABCA4-associated disease. Genetic testing identified three heterozygous ABCA4 variants: one pathogenic nonsense mutation, one likely pathogenic missense mutation, and one variant of uncertain significance. Segregation analysis was not possible due to lack of parental samples. Conclusions and importance: This case suggests that prior mitochondrial-toxic drug exposure may exacerbate the course of inherited retinal dystrophies, producing unusually severe panretinal degeneration. Clinicians should review medication history in patients with inherited retinal diseases and consider long-term retinal monitoring even years after discontinuing potentially toxic agents.