Differential Diagnosis for Bright Red Lesions on Buttocks

Single Most Likely Diagnosis

• Cellulitis: Given the description of bright red lesions with sharp margins and an "orange peel" appearance (peau d'orange), cellulitis is a strong consideration. This condition is characterized by a bacterial infection of the skin and subcutaneous tissues, often presenting with redness, warmth, swelling, and sometimes systemic symptoms like fever, although the patient is afebrile in this case.

Other Likely Diagnoses

• Contact Dermatitis: This could be a possibility if the lesions are due to an allergic or irritant reaction to something that came into contact with the skin. The "orange peel" appearance might not be as typical, but the sharp margins and bright red color could fit.
• Eczema (Dyshidrotic or Nummular): Certain types of eczema can present with well-demarcated, red lesions. However, the "orange peel" texture is less common in eczema.
• Psoriasis: Although less likely given the "orange peel" description, psoriasis can cause well-defined red plaques. The absence of scale might make this less likely, but it's worth considering.

Do Not Miss Diagnoses

• Necrotizing Fasciitis: Although the patient is afebrile, necrotizing fasciitis is a life-threatening condition that requires immediate attention. It can present with redness, swelling, and sometimes a peau d'orange appearance due to the underlying tissue destruction. The sharp pain out of proportion to the appearance is a key distinguishing feature, but it's not mentioned here.
• Erythema Multiforme: A skin condition characterized by target lesions, but it can sometimes present with atypical lesions. It's often associated with infections or medications.

Rare Diagnoses

• Lymphoma Cutis: Rarely, cutaneous lymphomas can present with red lesions, but they typically have a more chronic course and might not have such sharp margins.
• Kaposi's Sarcoma: This can cause red lesions, but they are usually more nodular and associated with immune suppression, particularly in HIV/AIDS patients.
• Angiosarcoma: A very rare and aggressive malignancy that can present with bruise-like lesions that might resemble the described "orange peel" appearance due to blood accumulation.

Treatment

The treatment would largely depend on the diagnosis. For cellulitis, antibiotics are the mainstay. For other conditions like contact dermatitis or eczema, removing the offending agent and using topical corticosteroids might be appropriate. In cases of necrotizing fasciitis, immediate surgical intervention and broad-spectrum antibiotics are crucial. Each condition's treatment is unique and requires a precise diagnosis for effective management.