Differential Diagnosis for a 23-year-old Female with Maculopapular Rash, Fever, and Sore Throat

• Single most likely diagnosis:
  • Infectious mononucleosis (caused by Epstein-Barr virus): This is a common illness in young adults, characterized by fever, sore throat, and rash, which often appears as a maculopapular rash. The combination of symptoms and the age of the patient make this a highly plausible diagnosis.
• Other Likely diagnoses:
  • Group A beta-hemolytic streptococcal pharyngitis with a rash (possibly scarlet fever): Although the rash in scarlet fever is typically more diffuse and erythematous, some cases can present with a maculopapular appearance. The recent sore throat supports this possibility.
  • Viral exanthem (such as roseola or enteroviral infection): These are common viral infections that can cause fever, sore throat, and a maculopapular rash in young adults.
  • Allergic reaction or drug rash: If the patient has recently started a new medication or been exposed to a new allergen, an allergic reaction could explain the rash and possibly the other symptoms if there's a systemic response.
• Do Not Miss diagnoses:
  • Kawasaki disease: Although more common in children, Kawasaki disease can occur in young adults and is characterized by fever, rash, and other systemic symptoms. It's crucial to consider this diagnosis due to the risk of cardiac complications if left untreated.
  • Secondary syphilis: This condition can cause a maculopapular rash, fever, and sore throat, among other symptoms. Given the potential for serious complications if untreated, it's essential to rule out syphilis, especially in sexually active individuals.
  • Meningococcemia: This is a severe infection caused by Neisseria meningitidis, which can present with a rash (often petechial or purpuric but can be maculopapular in early stages), fever, and sore throat. It's a medical emergency due to its high mortality rate if not promptly treated.
• Rare diagnoses:
  • Erythema infectiosum (Fifth disease): Caused by parvovirus B19, this typically presents with a "slapped cheek" appearance but can sometimes cause a more generalized maculopapular rash. It's less common in adults but can occur.
  • Acute HIV infection: Some individuals with acute HIV infection may develop a rash, fever, and sore throat as part of the initial seroconversion illness. This is a rare but important consideration, especially in individuals at high risk for HIV exposure.