Differential Diagnosis for Hives with Distinguished Border

• Single most likely diagnosis
  • Urticaria: This is the most common cause of hives and can present with a distinguished border. Urticaria can be acute or chronic and is often triggered by allergic reactions, infections, or autoimmunity.
• Other Likely diagnoses
  • Erythema multiforme: Characterized by target lesions with a distinguished border, often due to infections or medications. It's a skin condition that can sometimes resemble hives but has a more specific appearance.
  • Contact dermatitis: An allergic or irritant reaction to substances coming into contact with the skin, which can cause hives or rash with distinct borders.
  • Insect bites or stings: Can cause hives with distinct borders, especially if there's an allergic reaction to the bite or sting.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Anaphylaxis: Although it presents more systemically, anaphylaxis can start with hives and rapidly progress to a life-threatening condition. Early recognition is crucial.
  • Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN): These are severe skin and mucous membrane disorders, usually a reaction to medication or infection. They can start with what looks like hives but quickly escalate.
• Rare diagnoses
  • Malignant otitis externa: Though not typically presenting with hives, in rare cases, especially in diabetic or immunocompromised patients, it can cause skin manifestations with distinct borders due to the spread of infection.
  • Sweet syndrome (Acute Febrile Neutrophilic Dermatosis): Characterized by fever, neutrophilia, and tender, erythematous skin lesions that can mimic hives. It's rare and often associated with underlying conditions like infections, inflammatory bowel disease, or malignancies.