Measuring the epidemiology of distress: the rheumatology distress index

(1) To examine clinical and psychological variables to determine which are associated with psychologic and psychosocial severity or "distress"; (2) to investigate whether patients with the 2 major rheumatic disorders, rheumatoid arthritis (RA) and osteoarthritis (OA), differ in distress variables and distress; and (3) to develop and validate a simple, clinically acceptable index of distress suitable for routine care and research purposes.

A total of 2,403 patients were evaluated in 2 data sets (N = 1,399 and N = 1,490). The first data set was evaluated in the clinic by a routine clinical examination and administration of the Clinical Health Assessment Questionnaire (CLINHAQ). This instrument includes measures of pain, global severity, functional disability, anxiety, depression, sleep disturbance, fatigue, health satisfaction, and health status. The second data set was evaluated by a mailed questionnaire that included the CLINHAQ, but also coping scales, the Beliefs in Pain Control Questionnaire, the Self Performance Scale, and the Arthritis Helplessness Index.

RA and OA groups had similar scores for the variables associated with distress: pain, global severity, functional disability, anxiety, depression, sleep disturbance, fatigue, health satisfaction, and health status. Patients with fibromyalgia (FM) had more abnormal scores for every variable, reflecting overall distress. Using patients with FM as a "gold standard" of distress, we developed an index in data set 2. the Rheumatology Distress Index (RDI), made up of 5 variables, anxiety, depression, global severity, fatigue, and sleep disturbance, that best identified patients with FM compared to other patients. We then validated the instrument on the distress severity clusters formed in data set 1. The correlation between RDI and distress severity cluster was 0.874 with all patients considered and 0.867 with FM patients excluded. In addition, RDI predicted 1,174 of 1,399 (83.9%) cluster memberships correctly. Compared with a battery of psychological and clinical tests that classified 74% of FM and non-FM patients correctly, the RDI and is only slightly less effective, classifying 70.3% correctly.

Distress is a patient rather than a disease phenomenon. A simple, easy to administer self-report questionnaire can be used to classify patients according to their level of distress. The resulting index, the RDI. accurately identifies distressed and non-distressed patients. Such an index should be useful for patient care and research.