Board Review: Photodistributed Dermatoses

Overview / Definition Photodistributed dermatoses refer to a group of skin disorders that become exacerbated or triggered by ultraviolet (UV) radiation from sunlight. These conditions are often characterized by specific distributions on sun-exposed areas of the skin, leading to significant morbidity and impacting the quality of life for affected individuals. Epidemiology Photodistributed dermatoses can affect individuals of any age, gender, and ethnicity; however, certain conditions may exhibit demographic preferences. Commonly seen in adults aged 20-50. Women are more frequently affected than men, particularly in conditions like polymorphous light eruption. Incidence varies based on geographic location, with higher rates in areas with greater sun exposure. Pathophysiology / Mechanism The pathophysiology of photodistributed dermatoses is complex and varies among different conditions. Common mechanisms include: Immune response: Many photodistributed dermatoses involve a hypersensitivity reaction to UV radiation, leading to inflammation. Genetic predisposition: Certain genetic factors can increase the risk of developing conditions such as lupus erythematosus. Photoallergy: Some diseases are triggered by the formation of photoallergic compounds upon UV exposure. Clinical Presentation Clinical manifestations vary widely among different photodistributed dermatoses. Key features include: Polymorphous Light Eruption (PLE): Itchy papules and plaques primarily on sun-exposed areas, often occurring in the spring. Chronic Actinic Dermatitis: Erythema, scaling, and lichenification in sun-exposed areas, predominantly in older males. Lupus Erythematosus: Butterfly rash across the cheeks and nose, with potential systemic involvement. Porphyrias: Photosensitivity leading to blistering, scarring, and changes in pigmentation. Diagnosis / Workup Diagnosis is primarily clinical but may involve additional workup: History and Physical Examination: Detailed patient history regarding expos