Differential Diagnosis for Rash

• Single most likely diagnosis
  • Tinea versicolor: This condition is characterized by a non-pruritic rash that can appear on the trunk and in skin folds, and it can persist for years if left untreated. The fact that the rash is non-pruritic and has been present for over 2 years makes tinea versicolor a strong candidate.
• Other Likely diagnoses
  • Seborrheic dermatitis: This is a common skin condition that can cause a non-pruritic rash on the trunk and in skin folds. It often has a chronic course, which fits with the 2-year duration.
  • Pityriasis rosea: Although typically pruritic, some cases can be non-pruritic. It often starts with a herald patch followed by a widespread rash on the trunk, which could fit the description.
  • Contact dermatitis: This could be a possibility if the patient has been exposed to an allergen or irritant for an extended period, although it's less likely given the non-pruritic nature.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
  • Cutaneous T-cell lymphoma (Mycosis fungoides): This is a rare form of skin cancer that can present with non-pruritic patches or plaques, often in skin folds or on the trunk. Given its potential severity, it's crucial not to miss this diagnosis.
  • Secondary syphilis: This condition can cause a wide range of skin manifestations, including non-pruritic rashes on the trunk. It's essential to consider syphilis due to its serious consequences if left untreated.
• Rare diagnoses
  • Sarcoidosis: This is a systemic disease that can cause skin lesions, including non-pruritic rashes. It's less common but should be considered, especially if other systemic symptoms are present.
  • Granuloma annulare: This condition can cause non-pruritic skin lesions, often on the trunk or in skin folds, although it's more commonly seen in children and young adults.