Differential Diagnosis for Skin Pruritus during Sunlight Exposure

• Single Most Likely Diagnosis
  • Polymorphic Light Eruption (PMLE): This is the most common photodermatosis, characterized by an itchy, bumpy rash that appears after sunlight exposure. It's more prevalent in fair-skinned individuals and often occurs in the spring or early summer when sun exposure increases.
• Other Likely Diagnoses
  • Solar Urticaria: A rare condition where hives or itchy wheals appear on sun-exposed skin. It's an immune-mediated reaction to sunlight.
  • Phototoxicity: This occurs when certain medications (like antibiotics or antihistamines) react with sunlight to cause a skin reaction, which can include pruritus.
  • Photoallergic Contact Dermatitis: An allergic reaction to substances that become active when exposed to sunlight, leading to itchy skin lesions.
• Do Not Miss Diagnoses
  • Porphyria Cutanea Tarda (PCT): A disorder that can cause blistering, scarring, and pruritus upon sun exposure due to a deficiency in the enzyme responsible for heme synthesis. Missing this diagnosis could lead to significant morbidity.
  • Xeroderma Pigmentosum: A rare genetic disorder where the body is unable to repair DNA damage caused by UV light, leading to severe sun sensitivity, skin cancers, and potentially pruritus.
• Rare Diagnoses
  • Erythropoietic Protoporphyria (EPP): A rare genetic disorder causing increased sensitivity to sunlight, leading to burning pain, swelling, and potentially pruritus within minutes of sun exposure.
  • Chronic Actinic Dermatitis: A condition characterized by a persistent, itchy, eczematous eruption in sun-exposed areas, more common in older men.
  • Hydroa Vacciniforme: A rare photodermatosis of childhood, characterized by itchy, blistering lesions on sun-exposed skin.