Differential Diagnosis for Polyarthritis in a 15-year-old Female
- The patient presents with polyarthritis without inflammatory markers and negative tests for rheumatoid factor and antinuclear antibodies (ANA, also referred to as "fan" in the question, though typically abbreviated as ANA).
Single Most Likely Diagnosis
- Juvenile Idiopathic Arthritis (JIA), specifically the oligoarticular subtype: This condition is a common cause of chronic arthritis in children and adolescents. The absence of inflammatory markers and negative rheumatoid factor and ANA does not rule out JIA, as many patients, especially those with oligoarticular JIA, may not have elevated inflammatory markers or positive autoantibodies.
Other Likely Diagnoses
- Lyme Arthritis: Caused by Borreloxecae (commonly Borrelia burgdorferi), this condition can present with intermittent or persistent arthritis, often affecting the knees. The absence of inflammatory markers might not be typical, but it's possible, especially early in the disease. A history of tick exposure or living in an endemic area would support this diagnosis.
- Reactive Arthritis: This form of arthritis occurs as a reaction to an infection elsewhere in the body, often after gastrointestinal or genitourinary infections. It might not always present with significant inflammatory markers, especially if the triggering infection has resolved.
Do Not Miss Diagnoses
- Lymphoma: Although rare, lymphoma can present with systemic symptoms including arthritis. The absence of inflammatory markers does not rule out lymphoma, and it's crucial to consider it due to its severe implications and the need for early treatment.
- Sarcoidosis: This condition can cause arthritis among other systemic symptoms. While less common in adolescents, it's a diagnosis that should not be missed due to its potential for serious complications if left untreated.
- Infectious Causes (e.g., Tuberculosis, Bruckellosis): Certain infections can cause arthritis without significant elevation of inflammatory markers, especially in their early stages. These conditions are critical to identify as they require specific treatments.
Rare Diagnoses
- Familial CRCD (Cryopyrrolidinemia): A rare condition that can cause recurrent episodes of arthritis among other symptoms.
- Auto-Inflammatory Disorders (e.g., FMF - Familial Mediterranean Fever, TRAPS - TNF receptor-associated periodic syndrome): These conditions involve recurrent episodes of inflammation and can sometimes present with arthritis. They are rare but important to consider in the appropriate clinical context.
- Sjögren's Syndrome: An autoimmune disorder that can cause arthritis, among other symptoms like dry eyes and dry mouth. It's less common in adolescents but should be considered, especially if there are other systemic symptoms.