Brief Overview: The terms "undifferentiated arthritis" and "undifferentiated inflammatory arthritis" (UA) are used to describe patients with inflammatory arthritis that has not differentiated into a specific rheumatic disease, such as rheumatoid arthritis (RA) or psoriatic arthritis (PsA).
UA is most frequently used to describe patients during the first weeks to months following symptom onset, when it may not be possible to establish a specific diagnosis. However, UA also describes patients who fail to differentiate into another rheumatic disease, even after prolonged follow-up.
Prevalence: An undifferentiated arthritis (UA) is present in approximately a quarter to a third of patients presenting with early arthritis (ie, less than two to three months of symptoms). The incidence of UA ranges from 41 to 149 per 100,000 adults.
Etiology: Sometimes the cause of undifferentiated arthritis is unknown. Research indicates that autoimmune factors, genetics, infection, and smoking may be involved. Sometimes the cause becomes known later (which would lead to a new diagnosis) and can include: autoimmune diseases, infection, autoinflammatory disease, and rheumatological conditions.
Risk Factors:
- Family history, genetics
- Smoking
- History of viral infections
- Female gender
Commonly Associated Conditions:
- Rheumatoid arthritis (UA can progress to RA)
- Psoriatic arthritis
- Lupus
- Raynaud’s phenomenon
- Viral infection
Common Medications:
- csDMARDs – examples: methotrexate, sulfasalazine, hydroxychloroquine, leflunomide
- Low-dose Prednisone
- NSAIDs
Common Labs, Imaging, and Tests:
- Lab tests would be based on symptoms and any evidence of another condition. These would be used to rule out additional diagnoses and would be chosen/ordered based on which symptoms/features were present. Otherwise, if no symptoms are present suggestive of another rheumatic or inflammatory diagnosis, general screening labs may not be helpful. Some of these labs can include: RF, ANA, anti-CCP, Lyme antibodies, CBC, BMP, hepatic panel, CRP, ESR, urinalysis and urine sediment, CK, Hepatitis B&C serology
- Pre-treatment labs can include: CBC, BUN, creatinine, aminotransferases, ESR, CRP, rheumatoid factor (RF), anti-citrullinated peptide antibodies (ACPA)
- Imaging of the affected joints – ultrasound, MRI
- X-ray of the affected joint and the contralateral joint
- Arthrocentesis in patients with large joint (ex: knee, shoulder) involvement or the wrist
Common Symptoms:
- Morning stiffness
- Swelling of the joint(s)
- Joint pain
Common Treatments: Patients with UA must often start therapy before it is clear whether their disease will progress into another diagnosis, resolve spontaneously, or remain undifferentiated. Early treatment must be initiated to alleviate symptoms and to prevent the development of functional impairment caused by an untreated inflammatory arthritis.
- Medication (see above)
- Referral to rheumatology
- Physical and occupational therapy
Physical Findings:
- Joint swelling
- Warmth over the affected joints
- Synovitis may be present
- Tenderness to palpation of joints
- Joint effusion may be present
Potential Complications and Contraindications:
- Progression of symptoms to a more specific diagnosis (like RA)
- Medication side effects or intolerance
- Joint damage, decreased mobility, decreased independence
General Health and Lifestyle Guidance:
- Smoking cessation
- Try to stay physically active with low-impact exercises (e.g., swimming, yoga) – make sure to talk to your healthcare provider first about any exercise regimens you want to try
- Maintain a healthy weight to reduce joint stress
- Speak with your healthcare provider to find out if any specific diets may be recommended to help reduce symptoms
- Protect joints from strain or repetitive motion
- Communicate regularly with healthcare providers for symptom monitoring
Suggested Questions to Ask Patients:
- When did your joint symptoms begin, and are they improving or worsening?
- Are your symptoms worse in the morning or after periods of inactivity?
- Do you have a family history of autoimmune or rheumatic diseases?
- Have you had any recent infections, trauma, or major stressors?
- Have you noticed fatigue, fever, rashes, or dry eyes/mouth?
Suggested Talking Points:
- Undifferentiated arthritis means your symptoms don’t fit a specific diagnosis yet
- Make sure to report all symptoms to your healthcare provider to try to prevent joint damage
- Some patients will have resolution of symptoms, whereas some will progress to a more specific diagnosis
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