Looking at fibromyalgia differently - An observational study of the meaning and consequences of fibromyalgia as a dimensional disorder.

Despite data showing that fibromyalgia can be represented as a dimensional disorder, almost all assessments treat fibromyalgia as a dichotomous categorial disorder; and research shows that agreement between community diagnosis of fibromyalgia and fibromyalgia criteria is poor. We investigated the validity of FM as a discrete disorder by exploring the relationships of categorical fibromyalgia, the polysymptomatic distress (PSD) scale, and clinical variables. In a databank of 33,972 rheumatic disease patients, we studied the categorical diagnosis of fibromyalgia, the PSD scale separately and divided into severity groups, measures of widespread pain, as well as somatic syndrome questionnaires like the Patient Health Questionnaire-15 (PHQ-15), and clinical pain, global, HAQ disability and quality of life scales (EQ-5D). Clinical and demographic variables became more abnormal with increasing PSD score groups, indicating substantial increase in symptoms and pain. The changes across PSD categories were linear and large. When we compared FM- (PSD 8-11) with FM+ (PSD 12-18) patients we found considerable overlap in scores for pain, HAQ disability, patient global, PHQ-15, psychological status, and other variables. Somatic symptom scores were highly correlated with PSD (r=0.718). There was no evidence of a differential pain effect that was present in FM+ but not FM- subjects. Fibromyalgia is more accurately considered a dimensional than a dichotomous disorder. There is vast variability among fibromyalgia positive and negative cases that is governed by the strong and linear relationships between the dimensional PSD scale and clinical variables. The PSD scale provides measurements of the fibromyalgia dimension that support and enlighten categorical fibromyalgia and are an effective tool to measure clinical status and changes. Whatever the mechanism of the pain and symptom increase in fibromyalgia, it appears to operate over the entire fibromyalgia symptom dimension, not just in those with categorical fibromyalgia.

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