Thyrotoxicosis is characterized by the overproduction of thyroid hormone and in turn its action at the tissue level due to inappropriately high circulating thyroid hormone levels. Hyperthyroidism, a subset of thyrotoxicosis, refers specifically to excess thyroid hormone synthesis and secretion by the thyroid gland. It is a clinical state that results from any condition leading to high thyroid hormone action in tissues. It affects females more than men, approximately 2% of females and 0.2% of males. Although the condition is rare, the incidence increases with age. The clinical presentation varies, ranging from asymptomatic or subclinical, to life-threatening thyroid storm.
Subclinical hyperthyroidism/thyrotoxicosis
It is defined biochemically as the low levels of thyroid-stimulating hormone (TSH) and normal free thyroxine (FT4) and free triiodothyronine (FT3) concentrations. Patients can present with symptoms of thyrotoxicosis or they could be asymptomatic.
Overt primary thyrotoxicosis, It is a condition with suppressed TSH and with high levels of FT4, FT3, or both. Most commonly patients are presented with symptoms of hyperthyroidism.
Subclinical hyperthyroidism/thyrotoxicosis
It is defined biochemically as the low levels of thyroid-stimulating hormone (TSH) and normal free thyroxine (FT4) and free triiodothyronine (FT3) concentrations. Patients can present with symptoms of thyrotoxicosis or they could be asymptomatic.
Overt primary thyrotoxicosis
It is a condition with suppressed TSH and with high levels of FT4, FT3, or both. Most commonly patients are presented with symptoms of hyperthyroidism.
Hyperthyroidism
It is a form of thyrotoxicosis, which is caused by high synthesis and release of thyroid hormone by the thyroid gland. It is sometimes called overactive thyroid.
Thyrotoxic crisis (thyroid storm)
It is a severe form of thyrotoxicosis, which is acute with sudden collapse of homeostasis. It develops as a result of undiagnosed or inadequately treated thyrotoxicosis and involving altered mental status causing coma, cardiac and multiorgan failure, shock, and even death.
Signs & Symptoms Of Thyrotoxicosis:
Unexplained weight loss
Irregular heartbeat
Rapid heartbeat (tachycardia) — usually a heart rate higher than 100 beats per minute
Muscle weakness
Shakiness
Nervousness, anxiety, irritability
Heat intolerance
Changes in your menses
High grade fever
Diarrhea and feeling sick
Loss of consciousness or confusion, if severe
Eyelid retraction and stare
Optic nerve involvement in severe cases
Thin and fragile nails
Hair loss
Causes of Thyrotoxicosis:
There are many conditions that can cause thyrotoxicosis, namely:
Graves’ disease: It is the most common cause of hyperthyroidism -- and thyrotoxicosis. It leads the body’s immune system to attack the cells of your thyroid gland with antibodies mistakenly considering them as invaders. The etiology is not clear, but it makes the gland grow and make too much thyroid hormone. The condition tends to run in families, so the genes may play a vital role in whether you get it or not.
Nodules: These are small growths that can develop on your thyroid and affect the secretion of the hormone. There can be a single nodule and is called toxic nodular adenoma, or multiple nodules as the case in multinodular goiter or Plummer’s disease.
Struma ovarii: It is a rare type of ovarian tumor, which is made mostly of thyroid tissue. Data has shown that it can cause hyperthyroidism.
Thyroiditis: Any infection, viral or bacterial, some medications like lithium and amiodarone, or one’s own immune system can cause the inflammation of the thyroid gland and make it release excessive thyroid hormone into the bloodstream. It can also happen post delivery, after having a baby and the condition is called postpartum thyroiditis.
Thyroid Hormone Medication: Thyroid hormone is prescribed to treat a medical condition called hypothyroidism (in which thyroid doesn’t make enough hormone). You can have too much in your blood if your prescription is off or if it is not taken as prescribed.
Risk Factors:
Family history of thyroid disease, especially Graves’ disease
Female gender
Age above 60
Autoimmune diseases, like type 1 Diabetes, pernicious anemia and Addison’s disease
Diagnosis:
It requires:
A comprehensive history
Physical examination
Blood work
Imaging
Along with asking for signs and symptoms, inquiry about family history of thyroid problems, medication history, history of autoimmune disorders is crucial to reach to the causative factors. Evaluation of serum TSH levels and, if abnormal (low), FT4 and FT3 levels and examine the thyroid gland for enlargement or presence of any nodules in the parenchyma. Also TSH receptor antibodies (TRAb), that allow for a reliable differential diagnosis of autoimmune (Graves Disease) and non-autoimmune causes of thyrotoxicosis.
Imaging is required to have a definitive diagnosis. Various imaging modalities are available like ultrasonography of the thyroid gland, thyroid scan (scintigraphy), radioactive iodine uptake test and orbital CT scan or MRI if there is eye involvement. Moreover, cytology is also carried out in case of the nodules to classify them as malignant or non-malignant.
Treatment:
It is difficult to prevent thyrotoxicosis but it can be treated and the choice of treatment depends on the cause of thyrotoxicosis. Treatment options for thyrotoxicosis include:
Antithyroid drugs: Methimazole and propylthiouracil (PTU) block the thyroid from making hormones.
Radioactive iodine: It can be taken by mouth. The overactive thyroid cells absorb the radioactive iodine, which damages the cells. This causes the thyroid to shrink and reduce the thyroid hormone levels. This usually leads to permanent destruction of thyroid, which then causes hypothyroidism. Because of this, most people who receive this treatment have to take thyroid hormone drugs for the rest of their lives to maintain appropriate hormone levels.
Surgery: Sometimes it is recommended to remove the thyroid gland through surgery, which is called thyroidectomy. This will correct hyperthyroidism, but it will usually cause hypothyroidism. That is why people who undergo thyroidectomy have to take thyroid hormone drugs for the rest of their lives to maintain appropriate hormone levels.
Beta-blockers: These drugs block the action of thyroid hormones on the body. They help control symptoms, such as rapid heartbeat, anxiety and shakiness that are caused by thyrotoxicosis.
Glucocorticoids: Glucocorticoids are a type of corticosteroid and they inhibit the conversion of T4 to T3. Conditions like thyroiditis that cause pain, can be treated with glucocorticoids.
Complications of Thyrotoxicosis:
Atrial fibrillation, stroke and congestive heart failure
Thyroid storm- a life-threatening complication
Osteoporotic fractures - excessive thyroid hormone makes it difficult for the body to store calcium in the bones and bones need calcium in order to be strong and stable. Hence, brittle bones
Grave’s ophthalmology – blurring of vision, bulging or redness