Differential Diagnosis for Worsening Rash on Left Upper Arm
- Single most likely diagnosis
- Eczema (atopic dermatitis): The patient's symptoms of a worsening, itchy rash with a raised edge are consistent with eczema, a common skin condition characterized by inflammation and dryness. The lack of response to moisturizing creams does not rule out this diagnosis, as eczema can be resistant to topical treatments.
- Other Likely diagnoses
- Contact dermatitis: The rash's location on the upper arm and its itchy nature could suggest an allergic reaction to a substance that came into contact with the skin, such as a plant, metal, or chemical.
- Psoriasis: The raised edge and growth of the rash could be indicative of psoriasis, an autoimmune condition that causes skin cells to build up and form scales.
- Insect bite reaction: The itchy, raised nature of the rash could be a reaction to an insect bite, which can cause a localized skin reaction.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Cellulitis: Although less likely, cellulitis is a bacterial skin infection that can cause redness, swelling, and warmth, and can be life-threatening if left untreated. The patient's symptoms of a growing, raised rash could be indicative of a more serious infection.
- Lyme disease: The rash's appearance and growth could be consistent with erythema migrans, the characteristic rash of Lyme disease, which is caused by a tick-borne bacterial infection.
- Rare diagnoses
- Dermatofibroma: A rare, benign skin growth that can cause a raised, itchy rash.
- Granuloma annulare: A rare skin condition characterized by a ring-shaped rash with a raised edge, which can be itchy and grow over time.
- Cutaneous T-cell lymphoma: A rare type of skin cancer that can cause a variety of skin lesions, including itchy, raised rashes.