Differential Diagnosis for High Grade Fever with Chills, Arthralgia, and Erythematous Rash

Single Most Likely Diagnosis

• Viral Exanthem: This is a common condition characterized by a rash and fever, often accompanied by other symptoms like chills and arthralgia. The combination of high-grade fever, chills, arthralgia, and an erythematous rash is typical for various viral infections, making viral exanthem a leading consideration.

Other Likely Diagnoses

• Bacterial Sepsis: Sepsis can present with fever, chills, and systemic symptoms including arthralgia and rash, especially if the causative bacteria induce a toxin-mediated response.
• Lyme Disease: Caused by Borrelia burgdorferi, transmitted by tick bites, it can present with fever, arthralgia, and a characteristic erythema migrans rash.
• Rocky Mountain Spotted Fever (RMSF): A tick-borne illness caused by Rickettsia rickettsii, characterized by fever, headache, and a rash that can be erythematous.

Do Not Miss Diagnoses

• Meningococcemia: A severe infection caused by Neisseria meningitidis, which can rapidly progress from a flu-like illness with rash to septic shock and death. The rash can be erythematous and may evolve into purpura.
• Toxic Shock Syndrome (TSS): Caused by bacterial toxins, typically from Staphylococcus aureus or Streptococcus pyogenes, TSS presents with high fever, rash, hypotension, and involvement of three or more organ systems.
• Endocarditis: Although less common, infective endocarditis can present with fever, arthralgia, and a rash (e.g., Janeway lesions), especially in individuals with pre-existing heart conditions.

Rare Diagnoses

• Ehrlichiosis/Anaplasmosis: Tick-borne bacterial infections that can cause fever, chills, arthralgia, and sometimes a rash.
• Southern Tick-Associated Rash Illness (STARI): Characterized by a distinctive rash similar to erythema migrans, caused by the bite of the lone star tick.
• Kawasaki Disease: An acute febrile illness of childhood, characterized by fever, rash, conjunctivitis, and changes in the lips and oral cavity, which can sometimes present with arthralgia.

Each of these diagnoses should be considered based on the patient's history, physical examination, and laboratory findings to ensure accurate diagnosis and appropriate treatment.