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What Is Undifferentiated Arthritis?

Determining the Risk of Progression to Rheumatoid Arthritis

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Updated September 17, 2013

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While there are many types of arthritis, patients don't always fit into one of the well-established and well-known rheumatic disease categories. A patient may be in the early stages of inflammatory arthritis, yet the pattern of symptoms is not consistent with a specific type of arthritis. There may be overlapping symptoms which fit more than one rheumatic disease. When a patient has symptoms consistent with inflammatory arthritis but not a specific type, they are classified as having undifferentiated arthritis. It's a way of saying that no definitive diagnosis can yet be made.

Why Is Predicting the Course of Undifferentiated Arthritis Important?

It is estimated that 40-50% of patients with undifferentiated arthritis undergo spontaneous remission. Approximately 30% of people with undifferentiated arthritis develop rheumatoid arthritis, while the rest develop other conditions. Since the goal of treatment for patients with rheumatoid arthritis is to stop progression of the disease, it is helpful to try to predict which patients with undifferentiated arthritis are likely to develop rheumatoid arthritis.

In 2008, a prediction rule was developed in Europe and published in the journal, Arthritis & Rheumatism. With consideration given to a patient's age, gender, number of joints affected, duration of morning stiffness, CRP, rheumatoid factor, and anti-CCP, the risk of developing rheumatoid arthritis was highly predictable in patients with undifferentiated arthritis.

In 2010, the American College of Rheumatology collaborated with the European League Against Rheumatism to revise guidelines used to diagnose rheumatoid arthritis. The revised guidelines focused on earlier stages of the disease rather than late-stage characteristics which were consistent with persistent or erosive rheumatoid arthritis. According to the revised guidelines, definite rheumatoid arthritis is based on the confirmed presence of synovitis in at least one joint, the absence of another diagnosis that better explains the synovitis, and achievement of a total score of 6 or greater (out of 10) from individual scores in the following 4 assessments: number and site of affected joints (score range 0–5), serologic abnormality (rheumatoid factor or anti-CCP; score range 0–3), elevated acute-phase response (CRP or sedimentation rate; score range 0–1), and symptom duration (2 levels; range 0–1).

While radiographic assessment (i.e., x-rays or MRI), particularly of erosions of the hands and feet, can offer additional information to the diagnostician, they are time-consuming and not cost effective as a screening tool to predict the risk of developing rheumatoid arthritis in patients with undifferentiated arthritis.

The progression of rheumatoid arthritis is similar in patients who are first diagnosed with undifferentiated arthritis but go on to develop rheumatoid arthritis and those who are diagnosed with rheumatoid arthritis initially. Delaying treatment with disease-modifying anti-rheumatic drugs or biologic drugs in patients with undifferentiated arthritis may reduce inappropriate treatment of patients who will go on to experience spontaneous remission, but early treatment affords the best chance at preventing disease progression, disability, and decreased quality of life among those at risk for developing rheumatoid arthritis. That's why predicting risk helps to select patients who likely should not delay treatment.

To Delay or Not Delay? That's the Question.

There have been small studies that evaluated the use of disease-modifying anti-rheumatic drugs or biologics to prevent the progression of undifferentiated arthritis to rheumatoid arthritis. While results suggested that methotrexate and Orencia (abatacept) prevented progression to rheumatoid arthritis compared to placebo, Remicade did not. Larger studies are needed.

Sources:

2010 Rheumatoid Arthritis Classification Criteria: An American College of Rheumatology/European League Against Rheumatism Collaborative Initiative. Aletaha, Daniel et al. Arthritis & Rheumatism. August 10, 2010. DOI: 10.1002/art.27584
http://onlinelibrary.wiley.com/doi/10.1002/art.27584/abstract

Preventing the Progression From Undifferentiated Arthritis to Rheumatoid Arthritis: The Clinical and Economic Implications. Michael H. Schiff, M.D.. The American Journal of Managed Care. November 19, 2010.
http://www.ajmc.com/publications/supplement/2010/a307_10nov_ra/A307_10nov_Schiff_S243to48

Validation of a Prediction Rule for Disease Outcome in Patients With Recent-Onset Undifferentiated Arthritis. Arthritis & Rheumatism. van der Helm-van Mil, AHM, et al. Volume 58, Issue 8. August, 2008.
http://onlinelibrary.wiley.com/doi/10.1002/art.23681/pdf

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