Quantitative assessment of light discomfort thresholds in a patient with photoallodynia treated with topical naltrexone 0.01 %

Background Photoallodynia is a rare but disabling condition in which mild non-painful light triggers pain. Novel reliable diagnostic tools and effective treatments are desirable. Case presentation A 68-year-old female patient with dry eye owing to Sjogren syndrome reported severe photoallodynia not controlled by a wide armamentarium of topical treatments (eyelid hygiene, lubricants, corticosteroids, cyclosporine, and autologous serum). Patient symptoms were evaluated using visual analogue scale (VAS). Light discomfort thresholds under different lighting conditions (continuous warm, continuous cold and flashing warm) were measured using the Lumiz 100 device (Essilor International, Paris, France). All the evaluations were performed at presentation (T0), after proparacaine test (T1), and after 1 month of therapy with naltrexone 0.01 % eye drops instilled 4 times/day (T2). At T0, VAS score was 10; light discomfort thresholds were 1.83 log10[lux] for continuous warm, 1.79 log10[lux] for continuous cold, and 1.87 log10[lux] for flashing warm. At T1, a partial improvement of symptoms was reported and VAS score decreased to 8; light sensitivity thresholds slightly increased to 2.06 log10[lux] for continuous warm, 2.02 log10[lux] for continuous cold, and 2.18 log10[lux] for flashing warm. At T2, patient experienced a clinically meaningful improvement of symptoms and VAS score decreased to 4; in parallel, light discomfort thresholds increased to 2.78 log10[lux] for continuous warm, 2.82 log10[lux] for continuous cold, and 2.66 log10[lux] for flashing warm. Conclusions Naltrexone 0.01 % eye drops successfully controlled a severe case of photoallodynia refractory to all previous treatments. This improvement was quantitatively detected by the increase of light discomfort thresholds under all lighting conditions.