Differential Diagnosis for Hives with URI

• Single most likely diagnosis
  • Viral exanthem (e.g., viral urticaria): This is the most likely diagnosis as hives can be a common manifestation of a viral upper respiratory infection (URI), often caused by viruses such as rhinovirus, coronavirus, or respiratory syncytial virus.
• Other Likely diagnoses
  • Allergic reaction: An allergic reaction to a medication, food, or environmental allergen could cause hives and might coincide with a URI.
  • Autoimmune urticaria: This condition involves the immune system attacking the body's own tissues, leading to hives, and could be triggered or exacerbated by a URI.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Anaphylaxis: Although rare, anaphylaxis is a life-threatening allergic reaction that can cause hives, among other symptoms, and requires immediate medical attention.
  • Serum sickness: A rare immune system reaction to certain medications or antiserum, which can cause hives and other systemic symptoms.
  • Meningococcemia: A severe infection caused by Neisseria meningitidis, which can present with a rash (sometimes resembling hives) and is life-threatening if not promptly treated.
• Rare diagnoses
  • Urticarial vasculitis: An inflammation of the blood vessels that can cause hives and is associated with various conditions, including infections, autoimmune disorders, and medications.
  • Mastocytosis: A condition characterized by an accumulation of mast cells in the skin, which can cause hives and other symptoms, often triggered by viral infections or other factors.