Differential Diagnosis for Patient with Rash After Sun Exposure

The patient's symptoms of a rash all over the body after being out in the sun, accompanied by itching and the development of multiple scabs over three months, suggest several potential diagnoses. These can be categorized as follows:

• Single Most Likely Diagnosis

  • Polymorphic Light Eruption (PMLE): This is the most common photodermatosis, characterized by an itchy, bumpy rash that appears after sun exposure. The symptoms and history provided match closely with PMLE, making it a strong candidate for the single most likely diagnosis.

• Other Likely Diagnoses

  • Solar Urticaria: A condition where hives or itchy wheals appear on sun-exposed areas. While less common than PMLE, the presence of itching and the temporal relationship with sun exposure make this a plausible diagnosis.
  • Chronic Actinic Dermatitis (CAD): Also known as photosensitive eczema, CAD presents with a persistent, itchy, eczematous rash in sun-exposed areas. The chronic nature and the involvement of sun exposure fit the patient's symptoms.
  • Photoallergic Contact Dermatitis: This condition occurs when the skin reacts to a substance applied to the skin that becomes an allergen after exposure to sunlight. The rash and scabs could be consistent with this diagnosis, especially if the patient has been using new sunscreens, fragrances, or other topical products.

• Do Not Miss Diagnoses

  • Cutaneous T-Cell Lymphoma (CTCL): While less likely, CTCL can present with skin lesions that are exacerbated by sun exposure. Given the potential severity of this condition, it's crucial not to miss it, despite its lower likelihood.
  • Lupus Erythematosus: Systemic lupus erythematosus (SLE) can cause a photosensitive rash. Although the patient's symptoms do not fully align with SLE, the potential severity of the disease warrants consideration to avoid missing a critical diagnosis.
  • Porphyria Cutanea Tarda (PCT): A disorder that leads to blistering of the skin upon sun exposure, which can later crust and scar. The presence of scabs and the history of sun exposure make this a condition not to be overlooked.

• Rare Diagnoses

  • Erythropoietic Protoporphyria (EPP): A rare genetic disorder that causes sensitivity to sunlight, leading to burning pain, swelling, and blistering. The symptoms provided do not perfectly match EPP, but it remains a rare possibility.
  • Xeroderma Pigmentosum: A rare genetic disorder where the body is unable to repair DNA damage caused by ultraviolet (UV) light, leading to severe sunburn, blistering, and potentially skin cancer. The chronic and severe nature of the symptoms could align with this rare condition, although it is less likely given the age of onset and the specific symptoms described.