Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormone. It is a common condition that can often develop gradually over time. However, there are some causes that can lead to a sudden onset of hypothyroidism.
Thyroiditis
Thyroiditis refers to inflammation of the thyroid gland. There are several types of thyroiditis that can cause sudden hypothyroidism:
- Subacute thyroiditis: Also known as de Quervain’s thyroiditis, this is caused by a viral infection and usually resolves on its own over time.
- Postpartum thyroiditis: Develops in the first year after giving birth and is thought to be caused by changes in the immune system.
- Silent thyroiditis: Often follows a viral illness and can spontaneously resolve or lead to permanent hypothyroidism.
- Drug-induced thyroiditis: Certain medications like interferon-alpha, interleukin-2, lithium, and amiodarone can cause inflammation of the thyroid.
In thyroiditis, the inflamed thyroid gland leaks thyroid hormones stored in the gland, initially raising hormone levels in the blood. As the gland’s hormone reserves become depleted, hypothyroidism sets in. This hypothyroid phase can last for several months before normal thyroid function resumes.
Hashimoto’s Thyroiditis
Hashimoto’s thyroiditis is an autoimmune disorder in which the immune system mistakenly attacks the thyroid. This causes gradual destruction of the gland over time, eventually leading to reduced hormone production and hypothyroidism.
However, Hashimoto’s thyroiditis can sometimes cause an abrupt onset of hypothyroidism. This can happen after an episode of subacute thyroiditis or postpartum thyroiditis in people with underlying Hashimoto’s disease. The inflammation damages enough thyroid tissue to trigger significant hormonal changes rapidly.
Thyroid Surgery
Surgical removal of part or all of the thyroid gland will lead to abrupt hypothyroidism. This may occur after surgery for:
- Thyroid nodules
- Hyperthyroidism
- Thyroid cancer
- Goiter
Typically, hypothyroidism is expected after thyroid surgery. To prevent complications, levothyroxine replacement therapy is started immediately.
Radioactive Iodine Ablation
Radioactive iodine (RAI) ablation is a treatment used for hyperthyroidism, such as in Graves’ disease. It involves taking a dose of RAI, which gets absorbed by the thyroid gland where it destroys thyroid tissue.
RAI ablation causes intentional hypothyroidism so that the thyroid is no longer overactive. The decrease in thyroid function happens within the first few weeks after treatment.
Medications
Certain medications can disrupt thyroid function and cause hypothyroidism:
- Amiodarone: This antiarrhythmic drug contains a large amount of iodine and can inhibit thyroid hormone production and synthesis.
- Lithium: Used as a mood stabilizer, lithium can cause thyroiditis and reduce thyroid hormone secretion.
- Interferon-alpha: Used to treat hepatitis C and some cancers, it can trigger autoimmune thyroiditis.
- Immune checkpoint inhibitors: Newer cancer drugs like pembrolizumab and nivolumab modulate the immune system and carry a risk of inducing hypothyroidism.
Iodine Deficiency or Excess
The thyroid gland needs iodine to make thyroid hormone, but too little or too much iodine can disrupt thyroid function.
Sudden iodine deficiency from a low-iodine diet or after stopping iodine supplements can reduce thyroid hormone production. On the flip side, excess iodine from medicines, contrast dyes, diet, or supplements can also inhibit thyroid function.
Pregnancy
The increased hormone demands during pregnancy can unmask previously unrecognized mild hypothyroidism. As pregnancy progresses, more thyroid hormone is needed.
If the thyroid cannot keep up, overt hypothyroidism can develop abruptly. Postpartum thyroiditis can also strike after delivery, causing very low thyroid levels.
Pituitary Disorders
The pituitary gland secretes a hormone called TSH that controls thyroid hormone production. Pituitary gland injury, tumors, surgery, or radiation therapy can reduce TSH secretion and thyroid function.
Examples of sudden pituitary disorders leading to hypothyroidism include:
- Pituitary apoplexy (hemorrhage or infarction of pituitary tumor)
- Sheehan’s syndrome (postpartum pituitary gland necrosis)
- Head trauma
- Pituitary surgery or radiation
Conclusion
In summary, common causes of abrupt-onset hypothyroidism include thyroiditis, Hashimoto’s disease, thyroid surgery or RAI ablation, medications that affect thyroid function, iodine imbalance, pregnancy, and pituitary disorders. Many of these conditions damage the thyroid gland directly and impair its ability to produce sufficient hormones.
If hypothyroidism develops suddenly, it is important to seek medical care promptly for evaluation and treatment. Levothyroxine is usually effective at resolving symptoms and preventing complications when hypothyroidism is caught early.