Differential Diagnosis for High Fever, Leukocytosis, and Arthralgia

The combination of high fever, leukocytosis (an increase in white blood cell count), and arthralgia (joint pain) can be indicative of a wide range of conditions, from infections to autoimmune diseases. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Septic Arthritis: This condition, characterized by joint infection, often presents with high fever, leukocytosis, and severe arthralgia. The presence of these symptoms, especially if localized to a single joint, makes septic arthritis a leading consideration due to its potential for rapid joint destruction and the need for prompt antibiotic treatment.

• Other Likely Diagnoses

  • Rheumatoid Arthritis (RA): While RA typically has a more insidious onset, acute presentations can occur, especially in the context of a systemic flare, which might include fever and elevated white blood cell count alongside arthralgia.
  • Lyme Disease: Caused by the bacterium Borrelia burgdorferi, transmitted by tick bites, Lyme disease can present with fever, joint pain, and elevated white blood cell count, especially in its early stages.
  • Viral Arthritis: Certain viral infections, such as parvovirus B19, can cause arthralgia and arthritis, often accompanied by fever and leukocytosis.

• Do Not Miss Diagnoses

  • Endocarditis: Although more commonly associated with heart valve abnormalities and systemic emboli, endocarditis can present with fever, joint pain (due to immune complex deposition or embolic phenomena), and leukocytosis. Missing this diagnosis can be fatal.
  • Osteomyelitis: Bone infection can cause localized pain, fever, and elevated white blood cell count. While not always associated with arthralgia, adjacent joint involvement can occur, making it a critical diagnosis not to miss.
  • Meningococcemia: A severe infection caused by Neisseria meningitidis, it can present with fever, rash, and joint pain, alongside leukocytosis. This condition requires immediate recognition and treatment due to its high mortality rate.

• Rare Diagnoses

  • Adult-Onset Still's Disease (AOSD): A rare autoimmune condition characterized by high fevers, salmon-colored rash, and arthralgia, often accompanied by leukocytosis. It's a diagnosis of exclusion but should be considered in the appropriate clinical context.
  • Whipple's Disease: A rare, systemic bacterial infection (Tropheryma whipplei) that can cause fever, arthralgia, and a range of other systemic symptoms, including gastrointestinal and neurological manifestations.
  • Relapsing Polychondritis: An autoimmune disease that can cause inflammation of cartilaginous structures, leading to arthralgia, fever, and other systemic symptoms, including respiratory and auditory manifestations.

Each of these diagnoses requires careful consideration of the patient's history, physical examination, and laboratory findings to guide further investigation and management.