Introduction

Thyrotoxicosis is the overproduction of thyroid hormone, which is a treatable and manageable condition. This thyroid storm can range from an asymptomatic state to a life-threatening condition. It is often confused with hyperthyroidism. Hyperthyroidism is not the sole cause of this condition. Thyrotoxicosis may cause abnormal changes in the body, mainly hypermetabolism, abnormal functioning of the heart, weakening of bones also affects menstrual health. This is also the cause of abnormalities in reproductive health. Hyperthyroidism causes weight loss, anxiety, hyperreflexia, heat intolerance, diarrhoea, brittle hair, dry skin and palpitations.

What is thyrotoxicosis?

The increased production of Thyroid hormone, primarily triiodothyronine (T3) and thyroxine (T4), which controls the body's metabolism, is Thyrotoxicosis.

Causes

1. Hyperthyroidism (excessive production of thyroid hormone)
2. Graves’ disease (autoimmune condition): The exact cause of Graves’ disease remains unclear, but it might be due to genetic and environmental factors
3. Toxic multinodular goitre (enlarged thyroid): It is caused due to iodine deficiency and genetic factors. These nodules are multiple autonomously functioning nodules that produce excessive thyroid hormones independent of TSH regulation
4. Toxic adenoma (benign thyroid nodule): This is a single nodule, autonomously functioning within the thyroid gland that over secretes thyroid hormone
5. TSH-secreting pituitary adenoma (pituitary tumour): TSH-producing adenoma is a condition where TSH is suppressed and causes elevated TSH along with increased T3 and T4
6. hCG-mediated hyperthyroidism (mild and temporary condition that occurs in some pregnant women): HCG is structurally similar to TSH, thus by stimulating the TSH receptor, it causes hyperthyroidism, specifically during the first trimester of pregnancy or due to infertility treatments.
7. Thyroiditis (inflammation of the thyroid gland): In thyroiditis, after the hypothyroid phase, it will cause thyrotoxicosis, but usually thyroid functions normalizers following the process
8. Thyroid storm: It has a high mortality rate. In this condition, the TSH level will be low or undetectable (<0.01 mU/L) and elevated T₄ and T₃ levels¹
9. Nutritional disturbance: Increased iodine uptake²
10. Mental distress: Even though the exact mechanism is unknown, the stress increases cortisol levels, which will trigger the thyroid production²

Other factors concomitant to thyrotoxicosis are thought to be due to environmental exposures or triggers. There are a number of exposures that have been identified and proposed, are infections, life stress, iodine intake, smoking, medication use such as amiodarone and interferon, radiation, and environmental toxicants. Iodine is essential for thyroid hormone production, excess iodine, however, can also have adverse effects depending on underlying thyroid function, as well as the extent and duration of iodine excess. There are studies which found that smokers with irregular periods had higher T4 levels than those of the non-smokers. Lifestyle factors that showed the highest consistency in results between studies were smoking, BMI and iodine (micronutrient taken from the diet), leading to a decrease in TSH levels and an increase in T3 and T4 levels. Drug-induced thyrotoxicosis (iodine-rich drugs like amiodarone and immune checkpoint inhibitors).³

How thyrotoxicosis affects menstrual health

There is a complex physiological relationship between thyroid function and female reproduction. The factors like age (>60), sex (likely in females), and other underlying conditions complement the thyroid dysfunction. This condition is likely to develop during hormonal flux, like menopause, puberty and pregnancy, which may be due to oestrogens.⁴ Thyroid hormones directly affect the ovaries and act indirectly with sex hormone-binding globulin. In women with hyperthyroidism, total oestrogen levels may be 2- to 3-fold higher than compared of normal women during all menstrual cycle phases. Disruption of ovulation due to increased production of prolactin leads to menstrual irregularities and infertility.⁵ It’s not clear how autoimmune thyroid disease and hormonal dysfunction are related to thyroid disease, but the endocrine and immune mechanism is proven to negatively affect reproductive health.⁶

Diagnosis

Here are some observable thyrotoxic-associated menstrual abnormalities:⁷

• Amenorrhea:  Absence of menstrual cycle in both pre-puberty conditions (women who did not have their period before 15) and missing periods in women for certain months
• Oligomenorrhea:  Reduced menstrual flow (Regular menstrual flow will be from 5-7 days)
• Hypomenorrhea: There will be a 20% decrease in menstrual flow compared to regular periods
• Hypermenorrhea: a condition where more than a 20% increase in menstrual flow can be seen in comparison with the previous periods
• Menorrhagia: shows heavy menstrual bleeding

Biochemical and hormonal abnormalities can be evaluated by some tests includes:¹

• TSH (thyroid-stimulating hormone), which is usually low in people with thyrotoxicosis
• T3 (triiodothyronine) and T4 (thyroxine): Elevated levels may show hyperthyroidism
• Free T3 and T4: Elevated free T3 and T4 indicate thyrotoxicosis
• Autoantibody testing: For autoimmune conditions like Graves’ disease
• Radioactive iodine uptake studies or thyroid scans: help differentiate between causes of thyrotoxicosis other than Graves’ disease. A single toxic adenoma will show focal uptake in the adenoma, with suppressed uptake in the surrounding thyroid tissue. In toxic multinodular goitre, multiple areas of focal increased uptake are observed, with suppressed uptake in the surrounding tissue

The abnormal sexual development, abnormal uterine bleeding, infertility, delayed puberty, hirsutism, and recurrent miscarriages can be a possibility of thyroid dysfunction.

Treatments⁸

¹³¹Iodine: This treatment is suggested for females who are planning a pregnancy in 6-7 months after the therapy, when the hormone levels are normal. But before 48 hours of the treatment, a pregnancy test should be taken to avoid any complications.

Antithyroid drugs (ATDs): People with mild hyperthyroidism are treated with drugs to avoid re-emission. Drugs are preferred for pregnant women due to the risk of other methods. The non-invasive method also provides rapid relief from associated symptoms.

Surgery: After complete removal of the overactive thyroid gland, it provides immediate relief and definitive control of the condition. This method is preferred if there is an enlarged thyroid gland, co-existing hyperparathyroidism and in Graves’ eye disease. Also, if the female is planning pregnancy before the hormone levels are normal, this method can be chosen.

Complications

If the diagnosis and treatment of thyrotoxicosis have been delayed, then it can lead to thyroid storm. The person with any condition of the heart, brain and impaired liver functions should be evaluated for the factors that may cause complications. During pregnancy, radiotherapy should be avoided as it can cause complications with pregnancy.¹

Summary

Thyrotoxicosis affects major functions in the body, including reproductive health. The normal menstrual cycle interval is 28 days, but due to hyperthyroidism, the chances of absence of menstruation are common. By tracking periods, it's also possible to diagnose other conditions associated with thyrotoxicosis.  The abnormalities with menstrual flow are the major detector for the diagnosis, followed by the blood tests of thyroid hormones and in autoimmune conditions, antibody testing. To cure the condition, there are drugs which are preferred for the mild hyperthyroidism and other therapeutic methods for specific conditions like pregnancy and autoimmune diseases are followed in medicine to improve the individual’s health and safety.

FAQs

What is the connection between the menstrual cycle and thyrotoxicosis?

The excessively produced thyroid hormones in this condition can alter the menstrual cycle. Due to disruption of ovulation, light bleeding, missed periods and irregularity are very often seen.

Does thyrotoxicosis cause early menopause?

Yes, in severe conditions, early menopause is possible. If thyrotoxicosis is diagnosed and treated early, early menopause can be avoided.

How does thyrotoxicosis affect the menstrual cycle?

By increasing the metabolism, it disrupts the hormonal balance. Which causes irregular menstruation, absence of period and lighter bleeding.

How to diagnose thyrotoxicosis?

There are available blood tests for thyroid hormone levels like T3, T4 and TSH. Further can go with hormonal testing is available.

How to treat thyrotoxicosis?

There is radioactive iodine therapy, and antithyroid drugs are available to reduce the activity of the thyroid gland.