Hypothyroidism is a condition in which decreased thyroid hormone levels are observed in a patient. While this is not the same as Hashimoto’s disease, or autoimmune thyroiditis, Hashimoto’s can be an underlying cause of hypothyroidism. 

What is hypothyroidism?

Hypothyroidism is a clinical condition, or a syndrome, caused by a continuous deficit of thyroid hormones and a decrease in their effects on target organs. Hypothyroidism is one of the most common endocrine disorders. According to a large study that included over 17 thousands participants, hypothyroidism was found in 4.6% of the U.S. population aged 12 and older.1 There are several types of hypothyroidism which are caused by different reasons. 

What causes hypothyroidism? 

Primary hypothyroidism

Primary hypothyroidism develops when the thyroid gland is directly affected. Low levels of thyroid hormones trigger increased synthesis of thyroid stimulating hormones (TSH) in the pituitary gland as it tries to make the thyroid work. This is why, in patients with this type of hypothyroidism, TSH levels are higher than normal. The thyroid gland can become affected for сongenital anomaly of the gland development or acquired disorder2.

Acquired hypothyroidism may be caused by the following: 

  • An autoimmune disease; these disorders develop when the immune system erroneously attacks healthy tissue. The disorder when the immune system attacks the thyroid is called autoimmune thyroiditis, and it is the most common cause of hypothyroidism. 
  • Surgical removal of the thyroid gland.
  • Treatment with radioactive iodine.
  • Inflammatory processes.
  • Subacute, postpartum, asymptomatic thyroiditis.
  • Severe deficiency or excess of iodine. 
  • Intake of thyrostatic medications, lithium, and some other drugs.

Secondary hypothyroidism 

Secondary hypothyroidism develops as a result of the dysfunction of the adenohypophysis, the anterior lobe of the pituitary gland. This gland synthesizes hormones which regulate the work of other endocrine glands.

A man waiting for his doctor's appointment

As mentioned above, it produces the TSH which is responsible for the correct function of the thyroid. In case the pituitary gland is affected, it may produce decreased amounts of TSH, which will lead to thyroid dysfunction. 

Peripheral hypothyroidism

Peripheral hypothyroidism means that the thyroid releases enough hormones, but they are not adequately recognized by the body tissues. The issue may involve problems with hormonal transport or metabolism, as well as non-sensitivity of tissues to these hormones. Peripheral hypothyroidism is a very rare condition. 

What is autoimmune thyroiditis?

The purpose of the immune system is to attack pathological agents such as bacteria, viruses, or fungi. In patients with autoimmune diseases, the immune system erroneously attacks healthy tissue. This happens in Hashimoto’s disease, in which immune cells try to fight the thyroid tissue and secrete anti-thyroid antibodies. This leads to the destruction of thyrocytes, cells responsible for the synthesis of thyroid hormones. As a result, hypothyroidism develops. 

What causes Hashimoto’s disease? 

It is still unknown what exactly makes the immune system attack healthy tissue, but there are some known risk factors for Hashimoto’s disease. Some of them are listed below. 

  • Biological sex: females have issues with the thyroid gland about 7 times more frequently than males3.
  • Age: autoimmune thyroiditis is most prevalent in people between the ages of 30 and 50, although there have been cases of this diagnosis in younger people. 
  • Pregnancy: if a woman has had postpartum thyroiditis, she is at higher risk of developing AIT. 
  • Hereditary factor: the disease is related to genetics although no single gene responsible for it has been found. 
  • History of other autoimmune diseases, such as rheumatoid arthritis, celiac disease, and type 1 diabetes mellitus. 
  • Exposure to radiation: people who have been exposed to excessive radiation at any moment of their life have a higher risk of autoimmune thyroiditis. 

What are the symptoms of Hashimoto’s and hypothyroidism?

As we can see, autoimmune thyroiditis can lead to hypothyroidism, or a decrease in the synthesis of thyroid hormones. This means that both conditions have common manifestations. 

Thyroid dysfunction does not become evident quickly. Hypothyroidism develops slowly, and its first symptoms may not appear until months or even years later. To catch the disease during its  initial phase, regular checkups are very helpful.

Common symptoms of autoimmune thyroiditis include the following:

  • Increased fatigue that does not go away even after having rest
  • Muscle ache
  • Joint pain
  • Sleepiness
  • Frequent and long depressive conditions or mood swings
  • Trouble with memory and concentration
  • Face and neck swelling
  • Fragile nails; loss of hair and eyebrows
  • Intolerance of low temperatures
  • Excessively heavy and/or irregular periods
  • Fertility problems

Hashimoto’s disease and hypothyroidism: diagnostics 

The process of diagnosing hypothyroidism typically involves the following tests:  

  • Physical examination. Your healthcare provider will study your medical history and ask about your symptoms, as well as about any family history of problems with the thyroid gland (particularly in your mother or grandmother). In addition, your doctor will examine your neck for goiter, which sometimes develops in patients with hypothyroidism.
  • Echography. In cases of hypothyroidism, echography may reveal an enlargement of the thyroid and areas of thickening. 
  • Blood tests for T4 and TSH. In cases of hypothyroidism, the level of T4 may be too low and the level of TSH too high, although this is not always the case. 
A doctor explaining her patient Hashimoto’s disease diagnostics

Nevertheless, these tests are not enough for a diagnosis of Hashimoto’s to be established. To confirm the diagnosis, an additional blood test is necessary: a test for anti-thyroid antibodies. In Hashimoto’s disease, their level is usually high, even if the concentration of T4 is normal.

An increase in anti-thyroid antibodies accompanied by a normal level of hormones and no typical echographic changes of the thyroid is not enough to confirm AIT. Similarly, thyroid changes on an echography or a decreased level of T4 on their own are not sufficient. To make a correct diagnosis, all examinations and assessments should be studied cumulatively.

To sum up

  • Hypothyroidism is a condition in which the thyroid produces fewer hormones than the body needs for normal functioning. It can be caused by many factors, from pregnancy or having given birth recently to congenital anomalies. 
  • Hashimoto’s disease is autoimmune. It also often causes a decrease in concentrations of thyroid hormones, or hypothyroidism. 
  • To understand whether hypothyroidism is caused by an autoimmune reaction, an additional test for anti-thyroid antibodies is needed. This usually reveals an increase in these antibodies. 
  • Hashimoto’s disease can be confidently diagnosed only after a complex evaluation, which includes the patient’s complaints, blood tests for thyroid hormones and anti-thyroid antibodies, and an echography of the thyroid gland.