Background/Purpose:

Creatine kinase (CK) and Thyroid stimulating hormone (TSH) are frequently used tests in the diagnostic work-up of fibromyalgia (FMS) to exclude thyroid disease or myopathy. However, the diagnostic values of these tests in this clinical context are still unclear.

Methods:

All patients with suspected fibromyalgia, referred to the study hospital between November 2011 and April 2014 were asked to participate. Patients received a protocolized workup for FMS and exclusion of other disease using history, physical exam, neurological questionnaire, and additional testing when necessary. Patients with a previous diagnosis of thyroid disorder or a history of CK related disease were excluded.

Mean CK and TSH, percentage of abnormal CK and TSH values and the final diagnosis in patients with an abnormal CK or TSH value were used as outcome measures. An abnormal CK was defined as a CK >200 U/l for men and >170 U/l for women. Abnormal TSH was defined as a TSH <0.4 or >4.0 mE/l. Free Thyroid Hormone (FT4) was assessed when TSH was abnormal (reference values FT4: 8-22 pmol/l). The final diagnoses (ICD-9 code) were obtained from the patients’ files.

Results:

375 patients with suspected FMS were included (patient characteristics: table 1). Mean CK and TSH in these patients were 96 ± 50 mE/L and 1.8 ± 1.4 U/L respectively.

26 (6.9%; 95%-confidence interval (95%-CI) 4.3%-9.5%) patients had a borderline abnormal CK, considered clinically irrelevant. In 2 (0.5%; 95%-CI -0.2%-1.2%) patients CK value was clearly elevated and therefore retested, resulting in a normal CK value at this second test. In none of the patients with an abnormal CK a CK-related diagnosis was made and the final diagnosis was fibromyalgia in most of them (n=25).

13 (3.5%; 95%-CI 1.6%-5.3%) patients had an elevated TSH and 5 (1.3%; 95-CI 0.2%-2.5%) a lowered TSH, with one patient also having an abnormal FT4 value. However, the latter was deemed insignificant by the treating rheumatologist and the final diagnosis of all these patients was fibromyalgia.

Table 1 Characteristics of the patient population

Conclusion:

This study shows that abnormal CK and TSH values are rare in patients with suspected FMS referred to the hospital, and not resulting in another diagnosis as explanation for the complaints. Therefore, it seems that routine testing of CK and TSH levels, in secondary care, in all patients with suspected FMS does not contribute positively to the diagnostic process.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-value-of-routine-use-of-creatine-kinase-and-thyroid-stimulating-hormone-tests-in-patients-with-suspected-fibromyalgia-results-of-a-cross-sectional-study/