To investigate the relationship between control points and symptom and distress severity in fibromyalgia (FM).
Eighty-four new patients with FM seen at an outpatient rheumatology center from December 1994 through August 1996 underwent tender point and dolorimetry examinations at 18 active and 4 control sites. All completed the assessment scales for fatigue, sleep disturbance, anxiety, depression, global severity, pain, and functional disability, and a composite measure of distress constructed from scores of sleep disturbance, fatigue, anxiety, depression, and global severity -- the Rheumatology Distress Index (RDI).
Control point positivity was common in FM (63.1%) and was associated with somewhat more severe FM symptoms and general distress, yielding an increase in the RDI of 9.2 units or 0.55 standard deviation units. There was no evidence of particularly worse disease in patients with high counts of control tender points, and increasing numbers of tender points beyond the first positive control point were generally not associated with, or were only weakly associated with, increasing symptom severity. Many patients with positive control points had only mild levels of symptom severity. Finally, we found no clusters of patients with very severe symptoms associated with control points, or with dolorimetry scores, or with ratios of dolorimetry scores from different body regions of varying pain thresholds.
Positive control points are a common feature (63%) in FM, and appear to be a marker for a generally low pain threshold rather than a disproportionate increase in severe symptoms or distress. Control point positivity should not be used to disqualify a diagnosis of FM. Control point measurements do not add much to FM diagnosis or assessment and, perhaps, should be abandoned. At the least, they should be designated "high threshold" points rather than control points. Dolorimetry is considerably less useful in FM assessment than the manual tender point examination.