Differential Diagnosis

The patient presents with itchy bites that have evolved into hives, which have been persistent for 3 to 4 weeks. The symptoms worsen with hot water and have not responded to hydrocortisone. Here's a differential diagnosis based on the provided information:

• Single Most Likely Diagnosis
  • Insect Bite Reaction: This is the most likely diagnosis given the initial presentation of bites that later developed into hives. The reaction to insect bites can vary, and some individuals may experience more severe reactions, including the formation of hives around the bite site.
• Other Likely Diagnoses
  • Contact Dermatitis: This could be a possibility, especially if the patient has come into contact with an allergen or irritant that is causing the skin reaction. The fact that hydrocortisone did not provide relief could suggest a more complex dermatitis.
  • Urticaria: The description of hives around the bite sites could indicate urticaria, which can be acute or chronic. The triggers for urticaria can be varied, including insect bites, and the condition can be exacerbated by heat.
  • Eczema (Atopic Dermatitis): Although less likely given the acute onset, eczema could be considered, especially if the patient has a history of atopic conditions. The itchiness and the fact that symptoms worsen with hot water could support this diagnosis.
• Do Not Miss Diagnoses
  • Bullous Pemphigoid: An autoimmune skin disease that can present with itchy blisters, which might resemble hives. It's crucial to consider this diagnosis due to its potential for significant morbidity if left untreated.
  • Cutaneous Mastocytosis: A condition characterized by the accumulation of mast cells in the skin, leading to symptoms like itching, hives, and sometimes blistering. It's a rare condition but important to consider due to its potential impact on the patient's quality of life.
• Rare Diagnoses
  • Erythema Multiforme: A skin condition characterized by target lesions, which could be considered if the "hives" have a distinctive target-like appearance. It's often associated with infections or medications.
  • Papular Urticaria: A condition that presents with itchy papules, often as a result of an allergic reaction to insect bites. It could be considered if the patient's symptoms are primarily papular and itchy.

Each of these diagnoses should be considered and investigated further with a thorough medical history, physical examination, and potentially diagnostic tests to determine the underlying cause of the patient's symptoms.