Discussion: How to use RA predictors to aid patient well being today, tomorrow and beyond
For a rheumatologist, DAS (Disease Activity Score) is a commonly used clinical tool for the diagnosis of RA (rheumatoid arthritis). Diagnosing an RA patient can many times be a challenge, even for rheumatologists with many years of experience. At Sectra we offer the rheumatologist a complementary tool to monitor RA patients, we offer the technology DXR, a way of extracting information about the patient’s bone loss from a standard hand X-ray image.
We sometimes get the question how DXR compares to DAS as a predictor in patients with RA. I would say that they are not comparable since they measure different things in totally different ways.
DAS is a good indicator on how the patient feels right now. This is of course of great importance and a high DAS, also in absence of other predictors of future joint erosions indicates need of treatment. DAS does however not describe the status one week ago or one month ago – or the time in-between. Unless DAS is high over a long time, it seems not to be a predictor of future erosions and hence, a one- or two-time high DAS, with no other risk factors present, does probably not indicate a need for aggressive treatment, such as TNFα inhibitors.
DXR on the other hand describes a disease process over time. It is a fully objective automated measurement from regular hand X-ray images. Bone loss is measured from one time-point to another and the result is presented as a mean bone mineral density bone loss per month (mg/cm2/month). Elevated or highly elevated bone loss has been shown to be an independent predictor of future erosions, indicating that RA patients loosing elevated amounts of bone in the metacarpals should be treated with more tight control than those not losing bone. Several studies have also shown that aggressive treatment decrease metacarpal bone loss according to the same pattern that erosions are inhibited. This is another sign of bone loss being important in the disease progress of RA.
Rheumatologists must of course treat patients both according to how they feel now but also according to their future risk of RA associated joint destruction. The bone loss rate may vary during the period between two measurements and what you measure with DXR is the mean rate. For DAS you may catch a dip – or a peak! Hence, a patient with high DAS but low in other predictors, such as DXR bone loss, probably need treatment to have good life quality now (maybe not biologicals though) and a patient with low DAS but with other predictors of erosion (elevated DXR bone loss, erosions at baseline, ACPA/RF…) should be treated to prevent future/more erosions.
It is known that there is sometimes dissociation between clinical remission and erosions, suggesting that subclinical inflammation could be the clue. Clinical remission is hence not a promise of a good outcome. DXR can detect bone loss also in patients without clinical signs of inflammation, enabling the physician to make a more well-founded decision on treatment.
What I want to point at is that it should not be a question of using DAS or DXR. They are supposed to be used in combination but for different purposes. In this way rheumatologist are aided in their choice of treatment regimens for the well-being of the patient both today, tomorrow and the days to come.
