Differential Diagnosis for a Big Red Patch on the Right Back
- Single most likely diagnosis
- Contact dermatitis: This is a common condition that occurs when the skin comes into contact with an irritant or allergen, causing a red, itchy, and inflamed patch. The location on the back suggests possible contact with an allergen or irritant, such as a plant, insect bite, or a new laundry detergent.
- Other Likely diagnoses
- Eczema (atopic dermatitis): A chronic skin condition characterized by dry, itchy, and inflamed skin. It can appear anywhere on the body, including the back.
- Psoriasis: An autoimmune condition that causes red, scaly patches on the skin. It can appear on the back, elbows, or scalp.
- Insect bite or sting: A large red patch on the back could be the result of an insect bite or sting, especially if the person has been outdoors.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Cellulitis: A bacterial skin infection that can cause redness, swelling, and warmth. If left untreated, it can lead to serious complications, such as sepsis.
- Necrotizing fasciitis: A rare but life-threatening bacterial infection that can cause severe pain, redness, and swelling. It requires immediate medical attention.
- Erythema migrans (Lyme disease): A rash that can appear as a large red patch, often with a distinctive "bull's-eye" pattern. If left untreated, Lyme disease can lead to serious complications, such as arthritis and neurological problems.
- Rare diagnoses
- Pityriasis rubra pilaris: A rare skin condition characterized by reddish-orange patches on the skin, often accompanied by scaling and itching.
- Sweet syndrome: A rare condition characterized by sudden onset of fever, leukocytosis, and tender, erythematous skin lesions.
- Erythema multiforme: A rare skin condition characterized by target-shaped lesions, often triggered by infections or medications.