Differential Diagnosis for Unilateral, Horizontal, Linear, Erythematous Rash
- Single most likely diagnosis
- Shingles (Herpes Zoster): This is the most likely diagnosis due to the description of a unilateral, horizontal, linear, erythematous rash that is painful. Shingles typically presents with a painful rash that follows a dermatomal distribution, which could span from the abdomen to the back on one side of the body.
- Other Likely diagnoses
- Contact Dermatitis: This could be considered if the patient has come into contact with an irritant or allergen that has caused a linear, erythematous rash. However, the pain associated with the rash might be less severe compared to shingles.
- Lichen Striatus: A rare, inflammatory condition that can cause a linear, erythematous rash, but it is more common in children and not typically painful.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Necrotizing Fasciitis: Although extremely rare and unlikely given the description, any rapidly progressing, painful skin lesion or rash, especially if accompanied by systemic symptoms like fever, should prompt consideration of necrotizing fasciitis, a life-threatening condition.
- Erythema Multiforme: A skin condition characterized by target lesions, which can sometimes appear linear and can be associated with significant morbidity if not recognized and treated appropriately.
- Rare diagnoses
- Linear IgA Bullous Dermatosis: An autoimmune condition that can cause linear, erythematous lesions, but it is rare and typically involves blistering, which is not mentioned in the scenario.
- Phytocontact Dermatitis: Caused by plant allergens, this could result in a linear, erythematous rash if the patient has been in contact with certain plants, but it would be less likely to cause significant pain compared to shingles.