Differential Diagnosis for Red, Splotchy Rash
The patient presents with a red, splotchy rash that resembles hives, has been ongoing for a week, and appears to migrate across different parts of the body, including the arm, neck, and hip. Based on these symptoms, the following differential diagnoses are considered:
Single Most Likely Diagnosis
- Urticaria: This is the most likely diagnosis given the description of the rash as "somewhat hives" and its migratory nature. Urticaria, or hives, can be acute or chronic and is characterized by itchy, raised welts that can appear anywhere on the body and may move around.
Other Likely Diagnoses
- Contact Dermatitis: This condition could explain the rash if the patient has been exposed to an allergen or irritant that causes a reaction on the skin. The rash's appearance on different parts of the body could be due to varying exposures.
- Erythema Multiforme: A skin condition characterized by target-like lesions, which could initially be mistaken for hives. It's often triggered by infections or medications.
- Pityriasis Rosea: Although it typically starts with a herald patch, the subsequent rash could be mistaken for hives, especially if the patient doesn't recall the initial lesion.
Do Not Miss Diagnoses
- Meningococcemia: A life-threatening condition caused by Neisseria meningitidis, which can present with a rash that may initially resemble hives but quickly progresses. Early recognition is crucial for survival.
- Vasculitis: Certain types of vasculitis, like Henoch-Schönlein purpura or leukocytoclastic vasculitis, can present with a rash that might be mistaken for urticaria. These conditions can have serious systemic implications.
- Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS): A severe drug reaction that can present with a rash, fever, and systemic symptoms. It's crucial to identify and discontinue the offending drug.
Rare Diagnoses
- Sweet Syndrome (Acute Febrile Neutrophilic Dermatosis): Characterized by fever, neutrophilia, and tender, erythematous skin lesions. It's a rare condition that could be considered if other diagnoses are ruled out.
- Erythema Marginatum: A rare condition associated with acute rheumatic fever, presenting with a distinctive rash that might be confused with urticaria.
- Mastocytosis: A condition where there's an accumulation of mast cells in one or more organs, which can cause skin lesions that might resemble urticaria, among other symptoms.