Differential Diagnosis for Red Patch on Back
- Single most likely diagnosis
- Erythema migrans (Lyme disease): A round, expanding red patch that is warm to the touch and not painful, fitting the description provided. It often extends past the midline and can be a single lesion.
- Other Likely diagnoses
- Cellulitis: A bacterial infection of the skin that can cause redness, warmth, and swelling, although it is typically painful.
- Contact dermatitis: An allergic or irritant reaction to something that came into contact with the skin, which can cause a red, warm patch.
- Nummular dermatitis: A type of eczema that can cause round, red patches on the skin, although they are often itchy.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Erythema marginatum (Acute Rheumatic Fever): A rare but serious condition that can cause a red, expanding rash, often accompanied by other symptoms like fever and joint pain.
- Necrotizing fasciitis: A life-threatening bacterial infection that can cause redness, swelling, and warmth of the skin, although it is typically extremely painful.
- Rare diagnoses
- Erythema multiforme: A rare skin condition that can cause target-shaped red patches, although they are often accompanied by other symptoms like fever and mouth sores.
- Sweet syndrome (Acute Febrile Neutrophilic Dermatosis): A rare condition that can cause red, warm patches on the skin, often accompanied by fever and other systemic symptoms.