Effect of di-N-propylacetic acid (valproic acid) on the TSH response to TRH--a presumptive role for gamma aminobutyric acid

Severe fatigue due to valproate-induced hypothyroidism in a case of bipolar disorder

BACKGROUND

Valproate-induced hypothyroidism is a rare condition and has been considered asymptomatic. Here, we report a case of bipolar I disorder who developed symptomatic valproate-induced hypothyroidism.

CASE PRESENTATION

A 44-year-old woman with bipolar I disorder complained of severe fatigue after starting valproate. She showed a hormonal pattern of central hypothyroidism. Thyroid autoantibodies were negative, and no pituitary abnormality was seen on magnetic resonance imaging. After stopping valproate, her severe fatigue rapidly improved with normalizing thyroid function.

CONCLUSIONS

Our case suggests that valproate-induced hypothyroidism should be considered when patients complain of excessive fatigue under treatment with valproate.

Thyroid hormone and γ-aminobutyric acid (GABA) interactions in neuroendocrine systems

Thyroid hormones (THs) have critical roles in brain development and normal brain function in vertebrates. Clinical evidence suggests that some human nervous disorders involving GABA(gamma-aminobutyric acid)-ergic systems are related to thyroid dysfunction (i.e. hyperthyroidism or hypothyroidism). There is experimental evidence from in vivo and in vitro studies on rats and mice indicating that THs have effects on multiple components of the GABA system. These include effects on enzyme activities responsible for synthesis and degradation of GABA, levels of glutamate and GABA, GABA release and reuptake, and GABA(A) receptor expression and function. In developing brain, hypothyroidism generally decreases enzyme activities and GABA levels whereas in adult brain, hypothyroidism generally increases enzyme activities and GABA levels. Hyperthyroidism does not always have the opposite effect. In vitro studies on adult brain have shown that THs enhance GABA release and inhibit GABA-reuptake by rapid, extranuclear actions, suggesting that presence of THs in the synapse could prolong the action of GABA after release. There are conflicting results on effects of long term changes in TH levels on GABA reuptake. Increasing and decreasing circulating TH levels experimentally in vivo alter density of GABA(A) receptor-binding sites for GABA and benzodiazepines in brain, but results vary from study to study, which may reflect important regional differences in the brain. There is substantial evidence that THs also have an extranuclear effect to inhibit GABA-stimulated Cl(-) currents by a non-competitive mechanism in vitro. The thyroid gland exhibits GABA transport mechanisms as well as enzyme activities for GABA synthesis and degradation, all of which are sensitive to thyroidal state. In rats and humans, GABA inhibits thyroid stimulating hormone (TSH) release from the pituitary, possibly by action directly on the pituitary or on hypothalamic thyrotropin-releasing hormone neurons. In mice, GABA inhibits TSH-stimulated TH release from the thyroid gland. Taken together, these studies provide strong support for the hypothesis that there is reciprocal regulation of the thyroid and GABA systems in vertebrates.

Elevated thyrotropin in bipolar youths prescribed both lithium and divalproex sodium

OBJECTIVE

To examine the effect of combined lithium and divalproex sodium on thyroid-stimulating hormone (TSH) levels in children and adolescents with bipolar disorders and to identify risk factors for lithium-induced hypothyroidism.

METHOD

Bipolar youths aged 5 to 17 years participating in an open-label clinical trial received treatment with lithium and divalproex sodium for up to 20 weeks. TSH levels were measured at baseline and at the end of the study. Subjects were divided into two groups for analysis: group 1 had TSH levels of less than 10.0 mU/L at the end of the study and group 2 had TSH levels of 10.0 mU/L or more at end of the study.

RESULTS

Twenty of the 82 subjects (24.4%) showed TSH elevations of at least 10 mU/L within an average exposure of less than 3 months. The mean baseline TSH level for group 2 was significantly higher than for group 1 (2.97 [SD = 1.48] versus 2.05 [SD = 0.89], p <.05). Mean lithium levels at the end of the study were 1.00 mEq/L for group 2 compared to 0.76 mEq/L for group 1 (t = -2.41, p =.019).

CONCLUSIONS

Lithium is associated with significant rates of thyrotropin elevation in bipolar youths. Factors associated with elevation in TSH in lithium-treated subjects include a higher baseline TSH level and a higher lithium level. Close monitoring of thyroid function in children and adolescents taking lithium is recommended.

Serum thyroid hormones and blood folic acid during monotherapy with carbamazepine or valproate. A controlled study

Studies investigating the influence of antiepileptic drugs on thyroid hormones usually have compared patients chronically treated with antiepileptic drugs to controls. To date, this type of designs has produced divergent results both with regard to individual drugs and individual thyroid hormones. The present study comprised 31 patients with newly diagnosed epilepsy, commencing treatment with either carbamazepine or valproate. T3, T4, FT4, FT3, rT3, TSH, T3 resin uptake and blood folic acid, were determined before and during antiepileptic monotherapy, thus making the patient his own control. During treatment with carbamazepine, a significant decrease in T4, FT4, FT3, rT3 and TBG was observed. Valproate caused a decrease in T4, FT4 and T3. Neither of the drugs caused any changes in blood folic acid concentrations or persistent increases in the TSH values. None of the patients developed overt symptoms of hypothyreoidism. Conceivable mechanisms underlying these hormonal changes are reviewed.