Differential Diagnosis for Buttock to Posterior Thigh Erythematous Well-Circumscribed Patch
- Single Most Likely Diagnosis
- Contact dermatitis: This is a common condition that can occur due to an allergic reaction or irritation from substances like soaps, detergents, or certain fabrics coming into contact with the skin. The well-circumscribed nature of the patch suggests a localized exposure to an offending agent.
- Other Likely Diagnoses
- Psoriasis: Characterized by well-defined erythematous plaques, psoriasis can occur on the buttocks and posterior thighs. The presence of scaling can help differentiate it from other conditions.
- Eczema (atopic dermatitis): Although it typically presents in flexural areas, atopic dermatitis can appear anywhere, including the buttocks and posterior thighs, especially in adults. It may not always be as well-circumscribed as in the question but can be considered.
- Seborrheic dermatitis: This condition can cause erythematous patches in areas rich with sebaceous glands, including the buttocks, though it's less common here than on the face or torso.
- Do Not Miss Diagnoses
- Erythema migrans (Lyme disease): Although less common in this location, erythema migrans, the rash associated with Lyme disease, can appear as a well-circumscribed erythematous patch. Given its potential for serious complications if untreated, it's crucial not to miss this diagnosis.
- Cellulitis: While typically more diffuse and less well-circumscribed, cellulitis can present with erythema and should be considered, especially if there are signs of infection like warmth, swelling, or fever.
- Rare Diagnoses
- Erythema multiforme: A skin condition characterized by target lesions, which can sometimes appear as well-circumscribed patches. It's often associated with infections or medications.
- Fixed drug eruption: This condition causes well-defined, circular patches that recur at the same sites each time the offending drug is taken. The lesions can be erythematous and may appear on the buttocks or thighs.
- Granuloma gluteale infantum (or adultum): A rare condition characterized by reddish-brown to purple nodules or patches on the buttocks, more commonly seen in infants but can occur in adults.