New developments in the diagnosis of fibromyalgia syndrome: Say goodbye to tender points?
ABSTRACTThe Symptom Intensity Scale score can be used to identify and quantify fibromyalgia syndrome from information supplied by a simple questionnaire. In this paper, the author describes how this test was developed and argues in favor of its use in clinical practice in diagnosing fibromyalgia syndrome.
KEY POINTS
- The Symptom Intensity Scale questionnaire consists of two parts: a list of 19 anatomic areas in which the patient is asked if he or she feels pain (the total number of yes answers being the Regional Pain Scale score), and a visual analogue scale for fatigue.
- According to the Survey Criteria, a diagnosis of fibromyalgia can be entertained if the Regional Pain Scale score is 8 points or higher and the fatigue visual analogue scale score is 6 cm or higher.
- The number of tender points, a surrogate for diffuse pain, does not fully capture the essence of fibromyalgia syndrome, in which accompanying fatigue is often severe and nearly always present.
- The Symptom Intensity Scale is an accurate surrogate measure for general health, depression, disability, and death. Fibromyalgia syndrome diagnosed with this instrument implies that this illness carries increased medical risk.
How the Symptom Intensity Scale was developed
Wolfe (2003)25 mailed a survey to 12,799 patients who had rheumatoid arthritis, osteoarthritis, or fibromyalgia syndrome. The questionnaire asked respondents if they had pain in 38 articular and nonarticular anatomic regions and to complete a 10-cm fatigue visual analogue scale. He observed that pain in a subset of 19 primarily nonarticular sites differentiated fibromyalgia syndrome from the other two diseases. Calling the number of painful areas of these 19 sites the Regional Pain Scale, he analyzed this measure using Mokken analysis and Rasch analysis to ensure that the questionnaire was statistically valid.
Wolfe also showed that a score of at least 8 points on the Regional Pain Scale, combined with a score of at least 6 cm on the fatigue visual analogue scale, provided the best diagnostic precision consistent with a diagnosis of fibromyalgia syndrome. The combination of these two measures became known as the Survey Criteria.
Katz, Wolfe, and Michaud (2006)26 next compared the diagnostic precision of the Survey Criteria, the ACR criteria, and a physician’s clinical diagnosis. The clinicians made their clinical diagnosis by “considering the long-term patient-clinician experience [including] factors related to pain, tenderness, fatigue, sleep disturbance, comorbidity, and psychosocial variables,” or as I call it, the company fibromyalgia syndrome keeps (Table 2).7,14,16,20 The Survey Criteria (8 points or higher on the Regional Pain Scale plus 6 cm or higher on the fatigue visual analogue scale) showed a roughly 75% concordance among all three definitions in 206 patients with fibromyalgia syndrome. In a cohort with clinically diagnosed fibromyalgia syndrome, a Regional Pain Scale score of 8 or more had a sensitivity of 83.2%, a specificity of 87.6%, and a percent correct of 85.4%. The authors reported that a score of 6 cm or more on the fatigue visual analogue scale “was also at the optimum level” for diagnosing fibromyalgia, but they did not provide more information.
Wolfe and Rasker (2006),27 using these data, devised the Symptom Intensity Scale, the score of which is calculated as the fatigue visual analogue scale score plus half the Regional Pain Scale score, all divided by 2. The scale is therefore a continuous variable rather than a categorical one, and scores can range from 0 to 9.75.
The authors gave the questionnaire to 25,417 patients who had various rheumatic diseases and found that a score of 5.75 or higher differentiated fibromyalgia syndrome from other rheumatic diseases, identifying 95% of patients who would satisfy the Survey Criteria for fibromyalgia.
In addition, they found a linear relationship between the Symptom Intensity Scale score and key symptoms of fibromyalgia syndrome. Of even greater importance, the Symptom Intensity Scale score showed closer association with general health than scores on the Health Assessment Questionnaire, a 27-question patient activity scale, the Arthritis Impact Measurement Scale, or the Short Form-36. It also proved to correlate with mood, probability of having diabetes, need for hospitalization, history of or relative time to myocardial infarction, number of comorbidities, rate of disability, and risk of early death (relative risk 1.12, 95% confidence interval 1.10–1.14). The Symptom Intensity Scale is therefore a diagnostic tool as well as a simple measure of general health among all rheumatic disease patients.
IMPLICATIONS OF THE SYMPTOM INTENSITY SCALE
Three arguments provide a strong rationale for using the Symptom Intensity Scale in the outpatient clinic to investigate the biopsychosocial aspects of illness in our patients:
- It is a simple way to measure overall health
- It can uncover comorbid depression
- It can detect fibromyalgia syndrome in patients who have other diseases.
It measures overall health
Unlike instruments intended for a particular disease such as the Disease Activity Score, which measures disease severity only in rheumatoid arthritis, the Symptom Intensity Scale score can also be used as a measure of global health (or disease severity), and the Survey Criteria (8 or more on the Regional Pain Score and 6 or more on the fatigue visual analogue scale) can be used to establish diagnosis. In fact, instruments like the Disease Activity Score essentially ignore biopsychosocial issues that are captured by the Symptom Intensity Scale.27
By detecting fibromyalgia syndrome in our patients, we identify people with symptoms of pain and distress that do not easily fit the prevalent model of organic disease. Measures like the Disease Activity Score are specifically suited as end points in controlled efficacy trials, but if these are the only measures physicians use to estimate a patient’s health in the clinic, they do so at their own and their patient’s peril.27
Because the continuous Symptom Intensity Scale score strongly correlates with patient-perceived pain, depression, and general health, it is an ideal instrument for outpatient evaluation. It complements a complete patient history and physical examination by measuring biopsychosocial factors.
It uncovers comorbid depression
Rheumatologists do a woeful job of recognizing and diagnosing depression in patients with rheumatoid arthritis. Sleath et al28 found that patients with rheumatoid arthritis who were diagnosed with depression in the office were always the ones who initiated the discussion of that diagnosis. Their doctors did not elicit it.
Middleton et al29 found that patients with concomitant fibromyalgia syndrome and systemic lupus erythematosus (SLE) had higher depression scores than did SLE patients without fibromyalgia syndrome. Moussavi et al,30 writing for the World Health Organization about the findings of a 60-country survey, concluded: “The comorbid state of depression incrementally worsens health compared with depression alone, with any of the chronic diseases alone, and with any combination of chronic diseases without depression.”30
Worse health implies earlier death. Ang et al31 reported that a higher average 4-year depression scale score conferred a hazard ratio of 1.35 (P < .001) for earlier death among 1,290 rheumatoid arthritis patients followed for 12 years.
By using a test like the Symptom Intensity Scale to detect fibromyalgia syndrome alone or to detect it in patients with other diseases, we implicitly recognize the high likelihood of simultaneous depression. Recognition and treatment of depression will improve overall health.
