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ABSTRACT.
Introduction. All
symptoms and most objectively verified abnormalities of fibromyalgia are
common among patients with hypothyroidism or partial peripheral thyroid
hormone resistance. In treatment trials, thyroid hormone therapy has
reduced or eliminated fibromyalgia symptoms, and a long-term follow-up
study showed that improvement with thyroid hormone therapy lasted 1-to-5
years. In a previous study by the authors, solicited female fibromyalgia
patients had significantly lower resting metabolic rates and basal body
temperatures than matched healthy controls. In this study, the resting
metabolic rates and body temperatures of fibromyalgia patients previously
evaluated at a specialty metabolic clinic were compared with healthy
controls to whom they were matched.
Methods.
Fifteen female fibromyalgia patients and 15 healthy females served as
study subjects. Patients were clinical cases selected to match controls by
sex, age, weight, and activity level. Resting metabolic rate (RMR) was
measured by indirect calorimetry (MedGem®), basal body
temperature with digital thermometers, and body composition by
bioelectrical impedance. The mean measured resting metabolic rate (mRMR)
was compared to percentages of the mean predicted RMR (pRMR) by two
methods: fat-free weight (Sterling-Passmore equation: SP) and sex, age,
height, and weight (Harris-Benedict and Mifflin-St. Joer equations: HB and
MSt.J). Measurements were taken during the follicular phase of subjects’
menstrual cycles.
Results.
Patients had a lower mean mRMR (939.70 ± 216.04 kcal/d vs 1293.40 ±
166.34 kcal/d, p = 0.00001) and lower mRMRs as percentages of pRMRs
(SP: -26.91 ± 13.36% vs -6.826 ± 12.55%, p < 0.0001. HB:
-32.45 ± 13.48% vs -9.13 ± 9.51%, p = 0.0001; MSt.J: -27.96 ±
14.53% vs -5.089 ± 11.30%, p = 0.0002). Age and fat-free weight
accounted for 62% of variability in controls’mRMRs. Fat-free weight,
water as a percentage of body weight, and fibromyalgia symptom intensity
accounted for 83% of the variability of patients’ mRMRs. Patients’
mean basal body temperature was significantly lower than that of controls
(96.38 ± 0.98 F vs 97.54 ± 0.59 F, p = 0.001). Patients’ serum
free T3 level was significantly lower than that of controls
(3.18 ± 0.559 vs 3.75 ± 0.717 pg/mL, p = 0.023).
Conclusions.
The patient group had a lower mean mRMR and lower mRMR as percentages of
pRMRs. Patients also had a significantly lower mean basal body
temperature. Neither calorie restriction nor low fat-free weight accounted
for patients’ lower RMRs. As in the previous study, fibromyalgia
patients’ normal fat-free weight argues against low physical activity
with poor physical fitness as the mechanism of their low RMRs. Free T4,
free T3, and TSH levels did not correlate with fibromyalgia
measures or RMRs in either patient or control group. The lack of
correlation does not rule out inadequate thyroid hormone regulation as the
mechanism of the low RMRs because studies have not shown that these
laboratory values reliably predict RMR values. Lowe, J.C., Honeyman, G., and Yellin,
J.: Lower resting metabolic rate and basal body
temperature of
fibromyalgia patients compared to matched healthy controls.
Thyroid
Science, 1:CLS1-24, 2006.
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