Isolated Solar Angioedema: A Rare Case Successfully Treated With Dapsone.

Isolated solar angioedema (ISA) is an exceptionally rare photodermatosis characterized by transient, painless angioedema triggered by ultraviolet (UV) or visible light exposure, typically presenting without urticaria or pruritus, which complicates diagnosis and treatment. To date, fewer than 10 cases of ISA have been documented in the literature, and the most effective management strategies remain unclear. We describe the case of a 31-year-old woman who presented with recurrent, asymptomatic facial edema affecting her left cheek, perioral region, and eyelids after sun exposure. Each episode resolved within 24 hours without residual urticaria or systemic symptoms. The patient denied urticaria, pruritus, tongue swelling, or respiratory difficulties. Initial treatments, including cetirizine, montelukast, and prednisone, provided minimal relief, suggesting a mechanism beyond histamine-mediated pathways. Laboratory workup with normal complement C4 helped exclude hereditary angioedema, and C-reactive protein (CRP) was mildly elevated, consistent with a nonspecific inflammatory process. A diagnosis of ISA was made based on the consistent temporal relationship with sun exposure, the absence of urticaria, and the exclusion of alternative diagnoses. Given the patient's poor response to conventional therapies, dapsone was initiated due to its efficacy in other forms of idiopathic angioedema and chronic inflammatory dermatoses. Dapsone modulates inflammation by inhibiting neutrophil recruitment, suppressing prostaglandin and leukotriene activity, and scavenging reactive oxygen species. Since dapsone does not directly target the bradykinin pathway and primarily modulates inflammatory processes, its observed clinical benefit in this case may suggest involvement of alternative inflammatory pathways. After three months of therapy, the patient reported a notable decrease in the frequency and severity of flare-ups, as well as enhanced tolerance to sun exposure. This case suggests dapsone may represent a potential therapeutic option for ISA refractory to conventional antihistamines or corticosteroids, although further studies are needed. Awareness of this rare entity and the potential benefits of dapsone may help improve outcomes in patients presenting with refractory ISA.