Differential Diagnosis for Tinea Corporis and Lichen Planus

When differentiating between tinea corporis and lichen planus, it's crucial to consider various diagnoses based on their likelihood and potential impact on patient health. The following categories help organize the thought process:

• Single Most Likely Diagnosis

  • Tinea corporis: This is often the most likely diagnosis for a ring-shaped, itchy rash on the body, given its common occurrence and the typical presentation of lesions with a clear center.
  • Lichen planus: In cases where the rash is more purplish, polygonal, and flat-topped, and especially if it involves the mucous membranes or nails, lichen planus becomes a strong consideration.

• Other Likely Diagnoses

  • Eczema (atopic dermatitis): Can present with itchy, inflamed skin that might resemble tinea corporis or lichen planus, especially if the eczema is severe or has a distinct morphology.
  • Psoriasis: Although typically distinguished by its silvery scales, psoriasis can sometimes be confused with these conditions, particularly if the scales are minimal or if the psoriasis is in an early stage.
  • Nummular dermatitis: Characterized by coin-shaped patches of eczema, which can be mistaken for tinea corporis due to their shape.

• Do Not Miss Diagnoses

  • Lupus erythematosus: While less common, systemic lupus erythematosus (SLE) can present with skin manifestations that might be confused with lichen planus or tinea corporis. Missing this diagnosis could have severe consequences due to the potential for systemic involvement.
  • Cutaneous T-cell lymphoma (Mycosis fungoides): A rare form of skin cancer that can mimic various dermatoses, including eczema, psoriasis, and lichen planus. Early diagnosis is crucial for effective treatment.
  • Infectious diseases (e.g., leprosy, secondary syphilis): Certain infectious diseases can cause skin rashes that might be mistaken for tinea corporis or lichen planus. These conditions require prompt diagnosis and treatment to prevent long-term complications.

• Rare Diagnoses

  • Granuloma annulare: A benign condition that can cause ring-shaped lesions, similar to tinea corporis, but typically without the itching.
  • Sarcoidosis: A systemic disease that can cause skin lesions, among other symptoms. While rare, it's an important consideration due to its potential systemic implications.
  • Pityriasis rosea: Although it usually has a distinctive "herald patch" followed by a secondary eruption, in some cases, it might be confused with the other conditions listed here, especially if the typical pattern is not recognized.