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Significant Increase in Plasma Thyroid-Stimulating Hormone During Low-Frequency Repetitive Transcranial Magnetic Stimulation

Published Online:1 Jan 2011

To the Editor: Repetitive transcranial magnetic stimulation (rTMS) is efficacious in treatment-resistant depression when applied with high-frequency stimulation (HF-rTMS: 5 Hz to 25 Hz) over the left dorsolateral prefrontal cortex (PFC) and with low-frequency stimulation (LF-rTMS≤1 Hz) over the right dorsolateral PFC.1 rTMS is known to be painless and well-tolerated, and does not require, as a rule, either premedication or special biological monitoring.

However, rTMS seems to influence the hypothalamo-pituitary-thyroid axis. We report, here, the first case of thyroid-stimulating hormone (TSH) increase occurring during LF-rTMS for treatment of depression.

Case Report

A 60-year-old woman was hospitalized for a treatment-resistant depression lasting for 2 years. She was treated with T4, 100 μg/day, after complete thyroidectomy for a multinodular goiter 13 years ago. Her plasma TSH levels had been stable, between 1 and 2 mU/liter (normal range: 0.4–3.4) for a long time, as were her thyroid hormone levels. Antidepressants previously prescribed to the patient never affected her thyroid function. On admission, levels of TSH and free T4 were 1.560 mU/L and 13.3 pmol/liter (normal range: 9.8–18.8), respectively.

For her treatment-resistant depression, daily rTMS sessions from Monday through Friday were delivered over 6 weeks in addition to her latest antidepressant (venlafaxine). The patient received LF-rTMS (1 Hz) to the right dorsolateral PFC (360 pulses per session, 120% motor threshold), and blood thyroid levels were obtained each Wednesday at 7 A.M.

Her serum TSH rapidly increased after beginning rTMS, up to 5.19 mU/L, and remained abnormally elevated during the whole rTMS period. When rTMS treatment was stopped 6 weeks later, plasma TSH returned to normal. In this patient treated with T4, after thyroidectomy, free T4 levels remained unchanged during the rTMS treatment period.

Discussion

So far, very little is known on the impact of rTMS on hypothalamo-pituitary-thyroid axis.2 A slight increase in plasma TSH level, remaining in the normal ranges, has been reported in healthy volunteers and in depressed patients with HF-rTMS (5 Hz to 20 Hz).1,3,4 In our present case, we report a significant increase in plasma TSH, above normal range, during LF-rTMS (1 Hz) treatment. Because our patient had a history of thyroidectomy, this rise in TSH did not induce any increase in plasma T4 level. In patients with a normal thyroid gland, we may expect an increase in plasma T4 secondary to the LF-rTMS-induced rise in plasma TSH. Such an increase in plasma T4 level has been recently suspected by Osuch et al.5 during treatment of anxiety disorders by LF-rTMS. Thus, rTMS can have significant effects on the pituitary-thyroid axis that may potentially induce hyperthyroidism. Further studies are needed to assess the effects of rTMS on thyroid function.

Department of Psychiatry and Addictology, University Hospital of Dijon, France
Department of Endocrinology, University Hospital of Dijon, France
Department of Psychiatry and Addictology, University Hospital of Dijon, France

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