Differential Diagnosis for Elevated Lesion with Blanching

Single Most Likely Diagnosis

• Urticaria: A common condition characterized by itchy, elevated lesions with well-defined borders, often caused by allergic reactions or autoimmune responses. The blanching is due to the transient nature of the lesions, which can resolve and reappear.

Other Likely Diagnoses

• Insect Bite Reaction: Similar to urticaria, reactions to insect bites can cause elevated, blanching lesions, especially if there is an allergic component to the reaction.
• Contact Dermatitis: An allergic or irritant reaction to substances in contact with the skin, leading to elevated, sometimes blanching lesions, depending on the severity and type of reaction.
• Erythema Multiforme: A skin condition characterized by target lesions, which can appear as elevated and may blanch, often associated with infections or medications.

Do Not Miss Diagnoses

• Cellulitis: Although typically not well-demarcated, in early stages or certain types (like erysipelas), cellulitis can present with elevated, blanching lesions. It's crucial to differentiate from other causes due to its potential for serious complications if not treated promptly with antibiotics.
• Necrotizing Fasciitis: A severe infection that can initially present with skin lesions, including blanching and elevation, before progressing to more severe signs. Early recognition is critical due to its high mortality rate.

Rare Diagnoses

• Mastocytosis: A condition characterized by the accumulation of mast cells in the skin, which can lead to lesions that may blanch and urticate upon stroking (Darier's sign).
• Leukocytoclastic Vasculitis: A form of small vessel vasculitis that can present with palpable purpura but may also have blanching lesions in some cases, depending on the stage and severity of the disease.