Differential Diagnosis for Light Brown Rash on Lower Leg

• Single most likely diagnosis
  • Stasis dermatitis: This condition is common in individuals with poor circulation, varicose veins, or those who stand for long periods. The light brown rash, often accompanied by swelling and itching, is a typical presentation.
• Other Likely diagnoses
  • Eczema (atopic dermatitis): Can present with a light brown rash, especially if the skin has been scratched or rubbed, leading to post-inflammatory hyperpigmentation.
  • Contact dermatitis: An allergic reaction or irritant contact dermatitis could cause a rash on the lower leg, depending on exposure to allergens or irritants.
  • Tinea infection (ringworm): Although typically more circular and red, some fungal infections can present with a light brown appearance, especially if partially treated or in certain skin types.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
  • Malignancy (e.g., melanoma): Although rare, any new or changing skin lesion should be evaluated for malignancy, especially if there are other concerning features like asymmetry, irregular borders, color variation, diameter >6mm, or evolving.
  • Insect-borne illnesses (e.g., Lyme disease): Depending on geographical location and exposure history, a rash on the lower leg could be the initial presentation of a tick-borne illness.
• Rare diagnoses
  • Sarcoidosis: Can cause skin lesions, including rashes, but is less common and usually accompanied by systemic symptoms.
  • Pityriasis versicolor: A fungal infection that can cause discolored patches on the skin, though it's more common on the trunk and may not typically be described as a light brown rash on the lower leg.
  • Schamberg disease (progressive pigmentary purpura): A rare condition characterized by pigmented purpuric dermatosis, which could be considered in the differential for a light brown rash, especially if there are elements of purpura.