Differential Diagnosis for Skin Lesions

The patient presents with skin lesions on the arms and top of thighs, which have recurred, are irregularly shaped, and exhibit some redness without itchiness. The use of OTC cortisone cream has shown improvement. Based on these symptoms, the following differential diagnoses are considered:

• Single Most Likely Diagnosis

  • Eczema (Atopic Dermatitis): Given the recurrence, irregular shape, and redness of the lesions, along with the improvement with cortisone cream, eczema is a strong candidate. Eczema can present with a wide range of symptoms, including red, itchy, and inflamed skin, but the absence of itch in this case does not rule it out, as not all eczema is itchy.

• Other Likely Diagnoses

  • Contact Dermatitis: This condition could explain the skin lesions, especially if the patient has been exposed to new substances or allergens on the arms and thighs. The improvement with cortisone cream supports this diagnosis, as corticosteroids are a common treatment for contact dermatitis.
  • Psoriasis: Although psoriasis typically presents with well-defined, scaly plaques, some forms can be less typical, and the response to cortisone cream could fit this diagnosis. However, the absence of scaling and the specific locations might make this less likely.
  • Keratosis Pilaris: This condition causes small, rough patches on the skin, often on the arms and thighs, but it typically doesn't respond as well to cortisone cream and is often accompanied by a rough texture, which isn't mentioned.

• Do Not Miss Diagnoses

  • Skin Cancer (e.g., Basal Cell Carcinoma, Squamous Cell Carcinoma): Although less likely given the description and the response to cortisone cream, skin cancers can present in various ways, including as irregularly shaped lesions. It's crucial to not miss these diagnoses due to their potential severity.
  • Infectious Diseases (e.g., Cellulitis, Abscess): While the description doesn't strongly suggest an infectious process, especially given the lack of systemic symptoms and the response to cortisone, it's essential to consider these diagnoses, especially if the lesions were to suddenly change or worsen.

• Rare Diagnoses

  • Granuloma Annulare: A rare skin condition characterized by bumpy, ring-shaped lesions, which could fit the description of irregularly shaped lesions. However, it's less common and might not respond as predictably to cortisone cream.
  • Lichen Planus: An inflammatory condition that can affect the skin, presenting with purplish, itchy, flat bumps. While the patient's lesions are not itchy, variants of lichen planus exist, and it could be considered, especially if other diagnoses are ruled out.