Differential Diagnosis for the Patient's Condition

The patient's symptoms of full body hives, difficulty breathing, and the progression of symptoms from itchy to painful and fluid-filled after stopping prednisone, suggest an allergic or autoimmune reaction. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Urticarial Vasculitis: This condition is characterized by inflammation of the blood vessels and can present with hives that are painful and fluid-filled, distinguishing it from typical urticaria. The worsening of symptoms after stopping prednisone, a steroid used to reduce inflammation, supports this diagnosis, as vasculitis often requires ongoing immunosuppressive treatment.

• Other Likely Diagnoses

  • Angioedema: Although typically associated with swelling of deeper tissues, angioedema can present with hives and significant respiratory distress. The fluid-filled nature of the hives could be consistent with this diagnosis, especially if there's significant swelling.
  • Autoimmune Urticaria: This condition involves the immune system attacking the body's own tissues, leading to chronic hives. The symptoms worsening after stopping prednisone could indicate an autoimmune component.
  • Allergic Reaction: A severe allergic reaction could cause the initial symptoms, and the progression could be due to ongoing exposure to the allergen or a secondary reaction.

• Do Not Miss Diagnoses

  • Anaphylaxis: Although the patient has already been treated and the condition seems to have progressed beyond the initial anaphylactic reaction, anaphylaxis is a life-threatening condition that must be considered, especially with difficulty breathing and widespread hives.
  • Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis (SJS/TEN): These are severe skin conditions usually triggered by medications or infections. They can present with skin lesions, blisters, and detachment of the skin, which could be mistaken for fluid-filled hives. SJS/TEN are medical emergencies.

• Rare Diagnoses

  • Mastocytosis: A condition characterized by the accumulation of mast cells in one or more organs. It can cause a variety of symptoms, including hives, itching, and difficulty breathing, due to the release of histamine and other mediators from mast cells.
  • Erythema Multiforme: An immune-mediated skin condition that can be triggered by infections or medications. It presents with target lesions and can sometimes involve mucous membranes, but it's less likely given the description of fluid-filled hives.