Twenty-nine female patients with fibromyalgia were questioned about symptoms of cold intolerance and Raynaud's syndrome; objective documentation of coldinduced vasospasm was obtained by a Nielsen test. Twelve patients (41 %) had abnormal Nielsen test results, and 11 patients (38%) had elevated levels of platelet a2-adrenergic receptors. There was a positive correlation between the percentage of change in finger systolic pressure on cooling (Nielsen test) and the number of qadrenergic receptors. There was poor correlation between Raynaud's syndrome symptoms and an abnormal Nielsen test result. Digital photoplethysmography showed a normal waveform in 2 of 3 patients. We hypothesize that a subgroup of patients with fibromyalgia syndrome have an up-regulation of a2-adrenergic receptors as a cause of their exaggerated reaction to cold. Fibromyalgia is a common syndrome of musculoskeletal pain and fatigue; its pathogenesis is unknown. Despite the lack of any objective laboratory tests, it is frequently diagnosed in North American patients (1,2), and it is gaining increasing recognition in European populations (3,4). The recent publication of the American College of Rheumatology (ACR) diagnostic criteria should provide a uniform standard for future clinical studies (5). Although the current definition of fibromyalgia is disarmingly simplewidespread body pain and >9 (of 18) tender pointsmany patients have symptoms that are not related to the musculoskeletal system, such as irritable bowel, dry eyes, dry mouth, tinnitus, imbalance, and Raynaud's phenomenon (6). Symptoms suggestive of Raynaud's syndrome have been described in 30-53% of patients (73). We report here the quantitative measurement of cold-induced vasospasm and its association with an increased number of platelet aZadrenergic receptors in patients with fibromyalgia.
PATIENTS AND METHODS
Study population.Consecutive female patients attending the Rheumatology Clinic at the Oregon Health Sciences University (OHSU) were invited to participate in this study. Of the first 30 asked, 29 agreed to participate. All patients fulfilled previous criteria for a diagnosis of fibromyalgia (9). In retrospect, they would also have met the 1990 criteria published by the ACR (5). The demographics of the patients are shown in Table 1 .The normal control subjects for the digital hypothermic challenge test (Nielsen test) were all female staff at OHSU. Their mean ( t S D ) age was 42.9 2 5.9 years. These subjects did not have fibromyalgia or symptoms of Raynaud's phenomenon, nor were they currently using tobacco or other vasoactive substances. Controls for the