The assessment and importance of disease activity versus disease damage in patients with inflammatory myopathy.

To capture the totality of the effect of a disease on a patient, three aspects of the disease need to be assessed: 1) the disease activity (which is potentially reversible with treatment); 2) damage (defined as irreversible changes in anatomy, physiology, or function) accumulated since the onset of the disease, albeit from the disease itself, comorbid conditions, or as a result of therapy; and 3) the patient's perception of the disease, because this is frequently different from the physician's perception. A fine line exists between under-treating a patient, which may lead to an increase in disease activity, and over- treating a patient, with the risk of serious morbidity from inappropriate therapy. Distinguishing between activity and damage can be difficult and measures to ascertain this are discussed. Further developments are underway to assess the measures that should be used for the assessment of disease activity and damage.