Sensory thresholds and motor responsiveness in thyroid disease: their responses to treatment and warming

Potentials and Pitfalls in Analytical Headache Epidemiological Studies—Lessons to be Learned from the Head-HUNT Study

The number of epidemiological headache studies is rapidly increasing, and has accentuated the need to improve the quality of the way studies are performed and how results are interpreted. The aims of this review were to summarize the main findings from the Head-HUNT study, to describe strengths and limitations of the Head-HUNT approach and to discuss the significance of some of our findings. Head-HUNT included a large sample size of 51 383 participants that gave the opportunity to make analyses also of relatively rare conditions. The wide range of health-related information made it possible to adjust for many potential confounding variables. Blood samples for future genetic headache studies are available for a non-selected large group of individuals. The data show that among several factors that have been evaluated, age and gender were the two most clearly related to migraine, whereas analgesic overuse and the presence of some comorbid conditions were most strongly associated with the prevalence of chronic headache. Interesting relationships to blood pressure and thyroidstimulating hormone levels were also found. Methodological problems in headache epidemiological studies are discussed and, in particular, problems with causal inferences. Despite the limitations of the head-HUNT study, we believe that the results so far have provided clues to causes and preventive factors of headache that should be explored in other populations and in prospective studies.

Do high TSH values protect against chronic musculoskeletal complaints? The Nord-Trøndelag Health Study (HUNT)

The aim of this large cross-sectional population-based study was to examine a possible positive or negative association between thyroid dysfunction and chronic musculoskeletal complaints (MSC). Between 1995 and 97, all 94,197 adults in Nord-Trøndelag County in Norway were invited to participate in a health survey. A total of 64,787 (69%) responded to questions related to MSC, whereof thyroid-stimulating hormone (TSH) was measured in 34,960 individuals. These included a 5% random sample of women and men 20-40 years of age (n=2165), nearly all women above 40 (n=19,308), a random sample which included 50% of men older than 40 years (n=9983), and 3504 (97%) with self-reported thyroid dysfunction. Among the 64,787 participants, 30,158 (47%) who reported MSC continuously for at least 3 months during the past year where defined as having chronic MSC. Associations between thyroid dysfunction and chronic MSC were assessed in multivariate analyses, estimating prevalence odds ratios (ORs) with 95% confidence intervals (CIs). High TSH values were associated with lower prevalence of chronic MSC at ten anatomical sites among women with no history of thyroid dysfunction. Among these, chronic MSC was less likely (OR=0.6, 95% CI 0.4-0.8) if TSH >or=10 mU/L than in women with normal TSH (0.2-4 mU/L). Chronic MSC was less likely among women with high TSH values. The mechanism is unclear and, theoretically, may reflect a fundamental gender-specific relationship between TSH and pain perception in the central nervous system.

Thyroid hormone regulates excitability in central neurons from postnatal rats

A lack of thyroid hormone in the postnatal period causes an irreversible mental retardation, characterized by a slowing of thoughts and movements accompanied by prolonged latencies of several evoked potentials and slowed electroencephalographic rhythms. Here we show that in cultured hippocampal and cortical neurons from postnatal rats treatment with thyroid hormone not only up-regulates Na(+)-current densities but also increases rates of rise, amplitudes and firing frequencies of action potentials. Furthermore, we show that the regulation of the Na(+)-current density by thyroid hormones also occurs in vivo: recordings from acutely isolated cortical neurons obtained from hypothyroid, euthyroid and hyperthyroid postnatal rats showed that hypothyroidism decreases the ratio of Na(+) inward- to K(+) outward-currents while hyperthyroidism upregulates Na(+)-currents with respect to K(+)-currents. Our observation of a regulation of neuronal excitability by thyroid hormone offers a direct explanation for the origin of various neurological symptoms related to thyroid dysfunction.