A 52-year-old woman with systemic lupus erythematosus has been on hydroxychloroquine 400 mg daily (6.2 mg/kg real body weight) for 8 years. She is asymptomatic but routine screening ophthalmology reveals the fundoscopic appearance marked **B** in the diagram—a parafoveal ring of retinal pigment epithelium depigmentation with central foveal sparing. Which of the following best describes the pathophysiologic mechanism underlying this retinal toxicity pattern?
A. Mitochondrial cytochrome c oxidase inhibition resulting in selective parafoveal photoreceptor apoptosis
B. Binding of hydroxychloroquine to melanin in the RPE with accumulation, leading to disruption of lysosomal function and inhibition of autophagy in retinal cells
C. Immune-mediated destruction of retinal pigment epithelium triggered by hydroxychloroquine acting as a hapten
D. Direct photochemical injury to photoreceptor outer segments from ultraviolet light exposure potentiated by hydroxychloroquine
Explanation
Why option 1 is correct
The bull's-eye maculopathy pattern marked B in the diagram is the hallmark of hydroxychloroquine retinal toxicity. According to the AAO 2016 Revised Recommendations, hydroxychloroquine (and chloroquine) are 4-aminoquinoline compounds that bind melanin in the retinal pigment epithelium and accumulate over time. This accumulation disrupts lysosomal function and inhibits autophagy in retinal cells, leading to progressive photoreceptor and RPE damage in a parafoveal distribution (with foveal sparing in Caucasians). The pathophysiology is fundamentally one of lysosomal dysfunction and impaired cellular autophagy, not direct photochemical injury or immune mechanisms. This mechanism explains why toxicity is cumulative (duration >5 years) and dose-dependent (>5 mg/kg real body weight daily is the critical risk threshold).
Why each distractor is wrong
Option 2 (Photochemical injury): While hydroxychloroquine does accumulate in the retina, the toxicity is not mediated by potentiation of UV-induced photochemical damage. The mechanism is intracellular lysosomal dysfunction, not photochemistry. Hydroxychloroquine toxicity occurs regardless of sun exposure.
Option 3 (Immune-mediated/hapten): Hydroxychloroquine retinopathy is not an immune-mediated or allergic phenomenon. The patient's underlying SLE does not drive the retinal toxicity; rather, the drug itself causes direct cellular damage through lysosomal disruption. This would not explain the dose- and duration-dependent pattern.
Option 4 (Mitochondrial cytochrome c oxidase inhibition): While mitochondrial dysfunction may occur secondarily, the primary and established mechanism is lysosomal dysfunction and impaired autophagy, not primary mitochondrial enzyme inhibition. This distractor conflates hydroxychloroquine toxicity with other mitochondrial toxins (e.g., some antiretrovirals).
High-YieldNEET PG
Hydroxychloroquine binds melanin → lysosomal accumulation → autophagy inhibition → parafoveal photoreceptor/RPE loss with foveal sparing; risk rises sharply above 5 mg/kg/day and after 5 years; early toxicity is asymptomatic—screening by visual fields and OCT (not fundus photos) is essential.
AAO 2016 Revised Recommendations on Screening for Chloroquine and Hydroxychloroquine Retinopathy
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