What is the utility of MRI for identifying disease activity in myositis patients when physical exam and labs are inconclusive?

Agree with @Dr. First Last, however, I want to caution about sensitivity and specificity of muscle MRI for a particular situation you are suggesting i.e., to evaluate if patient has active or inactive disease, has not been studied or proven. The muscle MRI, in general, has good sensitivity and specificity at presentation or diagnosis especially in centers where it is more of a routine, however, in other centers, it may have lower sensitivity and specificity.

Again, for your particular patient, I...

In the course of treating myositis, imaging can help to provide clarity when labs and clinical exam are incongruent. Muscle enzymes are not always elevated in active muscle disease. This can be true in dermatomyositis, or other myositis where necrosis is not a prominent part of the process. Further, weakness may be present as a result of muscle damage, deconditioning, or even steroid myopathy. Another instance that can present as a conundrum are those who have localized muscle pain in the absenc...

Yes, I agree with @Dr. First Last that the results of an MRI should only be taken in the context of the rest of the clinical work-up. However, this really does point to the fact that we don’t have a great gold standard for disease activity and flares.

Just to give another perspective, in our center, we don’t do muscle biopsies to ascertain disease activity and are now only doing it for an unclear diagnosis or suspicion of an alternative diagnosis. For one, it is invasive and is only a focal sam...