Differential Diagnosis for a 50-year-old Male with Intermittent Inflammatory Arthritis of Knees/Ankles and Fevers

• Single Most Likely Diagnosis
  • Rheumatoid Arthritis (RA): This is a common autoimmune disorder that often presents with symmetric, inflammatory arthritis affecting the hands and feet, but can also involve knees and ankles. The presence of fevers and intermittent symptoms could be part of the disease's fluctuating course.
• Other Likely Diagnoses
  • Gout: Although gout typically presents with acute, monoarticular attacks, it can sometimes cause polyarticular symptoms and systemic inflammation, including fevers. The involvement of knees and ankles is common in gout.
  • Psoriatic Arthritis (PsA): This condition often presents with asymmetric, inflammatory arthritis, and can involve any joint, including knees and ankles. The presence of psoriasis, dactylitis, or enthesitis can support this diagnosis, though not all patients have obvious skin manifestations.
  • Reactive Arthritis: Following a gastrointestinal or genitourinary infection, reactive arthritis can develop, characterized by inflammatory arthritis, often affecting the knees and ankles, and sometimes accompanied by systemic symptoms like fever.
• Do Not Miss Diagnoses
  • Lyme Arthritis: Caused by Borrelia burgdorferi, Lyme disease can lead to intermittent, inflammatory arthritis, particularly of the knee, and may be accompanied by systemic symptoms such as fever. Early recognition is crucial for effective treatment.
  • Septic Arthritis: Although typically presenting as a monoarticular condition, septic arthritis can be life-threatening and requires immediate diagnosis and treatment. The presence of fever and inflammatory arthritis, especially if acute in onset, should prompt consideration of this diagnosis.
  • Hematologic Malignancies (e.g., Lymphoma): Certain cancers can present with systemic symptoms, including fevers and arthritis. Although less common, these conditions are critical to identify due to their significant impact on prognosis and treatment.
• Rare Diagnoses
  • Adult-Onset Still's Disease (AOSD): Characterized by high fevers, salmon-colored rash, and inflammatory arthritis, AOSD is a rare condition that can mimic other rheumatologic diseases but has a distinct set of criteria for diagnosis.
  • Sarcoid Arthritis: Part of sarcoidosis, a systemic granulomatous disease, sarcoid arthritis can present with inflammatory arthritis and systemic symptoms, including fevers. It is less common but should be considered, especially if other systemic manifestations of sarcoidosis are present.
  • Whipple's Disease: A rare, systemic bacterial infection caused by Tropheryma whipplei, which can lead to arthritis, fever, and other systemic symptoms. Diagnosis is challenging and often requires intestinal biopsy.