Objectives From previous studies, it is known that the association between fibromyalgia and thyroid autoimmunity diseases exists. On the other hand, it was recently suggested that in many cases thyroid hormone treatment might be unnecessary. The aim of our study is to explore the thyroid hormone treatment among fibromyalgia patients in cross-sectional study based on data from fibromyalgia patients in the city of Nokia Health Center Finland.
Method Fibromyalgia patients were searched from the electronic patient records. Patients filled five questionnaires and information from electronic patient records was gathered.
Information from thyroid hormone treatment and thyroid-stimulating hormone (TSH) and free thyroxine (T4-V) levels were gained from patient records. We used the Finnish guidelines for hypothyroidism: TSH level over 4.2 mU/l was defined as subclinical hypothyroidism if the T4-V level was normal. The T4-V level under 11.0 pmol/L was defined as central hypothyroidism if TSH level was normal or low. TSH level over 4.2 mU/l and T4-V level under 11.0 pmol/L was defined as overt hypothyroidism. TSH levels between 0.27–4.2 mU/l and T4-V levels between 11.0–22.0 pmol/L were defined as normal thyroid function. Cross-tabulation and Chi-Square test were used when categorical variables were present and two-sample t-test was performed with variables following a normal distribution.
Results Altogether 208 patients were identified. 103 patients returned mailed questionnaires and were included in the study. 96 patients had fibromyalgia according to ACR 2010 criteria. From that group 33 (34%) had thyroid hormone treatment and 63 (66%) had not. Statistical significance was not found between those taking thyroid hormone replacement and those not taking it in functional ability (p=0.36) or depression (p=0.71). From those 33 patients with thyroxine treatment, 16 had information regarding the initial TSH and T4-V levels before thyroid hormone treatment: Ten (63%) patients had hypothyroidism based on the laboratory tests. Subclinical hypothyroidism was present in six cases, central hypothyroidism in three cases and as overt hypothyroidism in one case. Of 16 patients with thyroid hormone treatment, six patients (37%) had normal thyroid function at the beginning of the treatment.
Conclusions The occurrence of thyroid hormone treatment was much higher in our study population (34%) than in the previous study in Japan (8%). In our study, over one third of the fibromyalgia patient using thyroid hormone treatment – whose initial thyroid hormone levels were available – did have normal thyroid function. There are likely several explanations to this. One might be that one of the main symptoms of fibromyalgia is fatigue, which also is common with hypothyroidism. Patients are aware of this and some may want to try out the thyroid hormone treatment even though their thyroid function is normal. Further studies are needed to confirm the potential association between functional syndromes like fibromyalgia and inappropriate thyroid hormone treatment.
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