Differential Diagnosis for Fever with Rheumatoid Factor (RF) Positive
Single Most Likely Diagnosis
- Rheumatoid Arthritis (RA): This is the most likely diagnosis because RF is a common autoantibody found in the majority of patients with RA, especially those with more severe and longstanding disease. The presence of fever, along with joint symptoms such as morning stiffness, swelling, and pain, would strongly suggest RA.
Other Likely Diagnoses
- Systemic Lupus Erythematosus (SLE): SLE can present with fever, joint pain, and a positive RF. It's a multisystem autoimmune disease that can affect various parts of the body, including the skin, kidneys, and nervous system.
- Sjögren's Syndrome: This autoimmune disorder primarily affects the glands that produce tears and saliva but can also present with systemic symptoms like fever and have a positive RF.
- Mixed Connective Tissue Disease (MCTD): MCTD has features of several autoimmune diseases, including lupus, scleroderma, and rheumatoid arthritis, and can present with fever and a positive RF.
Do Not Miss Diagnoses
- Endocarditis: Although less common, infective endocarditis can present with fever and a positive RF due to the formation of immune complexes. It's crucial to consider this diagnosis because of its high mortality rate if left untreated.
- Lymphoma: Certain types of lymphoma, particularly those associated with autoimmune phenomena, can present with fever and a positive RF. Early diagnosis is critical for effective treatment.
- Hepatitis C: Chronic hepatitis C infection can lead to the production of RF and present with systemic symptoms including fever. It's essential to consider this diagnosis due to the availability of effective antiviral treatments.
Rare Diagnoses
- Scleroderma (Systemic Sclerosis): While scleroderma can present with a positive RF, it is less common than other autoimmune diseases. It's characterized by thickening of the skin and involvement of internal organs.
- Polymyositis/Dermatomyositis: These inflammatory muscle diseases can have a positive RF and present with fever, muscle weakness, and skin rash.
- Parvovirus B19 Infection: This viral infection can cause a positive RF and present with fever, especially in adults. It's known for causing the "fifth disease" in children but can have different manifestations in adults.