ABSTRACT
In a previous retrospective study, thyroid function tests were used to classify 38 fibromyalgia patients according to thyroid status. Results were consistent with euthyroidism (nonnal thyroid status) in 14 patients (36.8%), primary (thyroidal) hypothyroidism in 4 patients (10.5%), and central (hypothalamic or pituitary) hypothyroidism in 20 patients (52.6%). In this prospective study, an additional 54 patients were tested. Results were consistent with euthyroidism in 26 patients (48.1%), primary hypothyroidism in 8 patients (14.8%), and central hypothyroidism in 20 patients (37.0%). All patients from both studies were combined into a group of 92 to obtain the total percentage in each classification. Results were consistent with euthyroidism in 40 patients (43.5%), primary hypothyroidism in 12 patients (13.0%), and central hypothyroidism in 40 patients (43.5%).
There was no statistical difference in either study for the mean intensity of fibromyalgia symptoms (measured by visual analog scales) or the mean tender point score (measured with algometry) between any of the categories of patients. In the study of 54 patients, there was also no statistical difference for pain distribution (measured by the percentage of 36 body divisions containing pain), functional ability (measured by the Fibromyalgia Impact Questionnaire), or depression (measured by Zung's Self-Rating Depression Scale) between the three categories of patients.
In both studies, the percentages of patients with primary and central hypothyroidism were extremely high compared to those in the general population (see Table 1). Of the 92 patients, 52 (56.5%) had laboratory test results consistent with hypothyroidism. Contrary to anecdotal reports, hypothyroidism is extraordinarily common among fibromyalgia patients.