To determine the most appropriate means to assess the response to treatment in terms of pain and functional impairment in a chronic rheumatic condition (knee osteoarthritis [OA]) and an acute rheumatic condition (rotator cuff syndrome [RCS]).
Two prospective studies were conducted consisting of 1,019 outpatients with knee OA and 271 patients with acute RCS. The minimal clinically important improvement and the patient acceptable symptom state were determined for knee OA pain using a visual analog scale, and for knee OA function using the Western Ontario and McMaster Universities Osteoarthritis Index function subscale; for acute RCS pain, a numeral rating scale was used, and the Neer function subscale was used for RCS function.
The minimal clinically important improvement was shown to be the change required to achieve the patient acceptable symptom state, whatever the baseline level of symptom, the outcome (pain or function), or type of condition (chronic or acute). This acceptable state for pain was higher for chronic (27.0-36.4 across the baseline score) than acute (16.7-24.1) conditions. The level of functional impairment considered satisfactory by patients with knee OA was higher for more disabled patients (43.1) than for less disabled patients (20.4).
Patients consider that they experienced an important improvement only if this improvement allowed them to achieve a state they consider satisfactory. The most appropriate means to assess the response to therapy seems to be to assess whether patients feel good (i.e., achieve the patient acceptable symptom state).