What is Hashimoto's Thyroiditis?
Hashimoto's Thyroiditis (Autoimmune Thyroiditis) is the most common cause of thyroiditis.It is associated with autoantibodiesand self-reactive CD4 Tcells.Antithyroglobulin and antiperoxidase antibodies are raised in more than 90% and 70% respectively.The condition was first described in 1912 by Hakaru Hashimoto, a Japanese physician who studied four patients with chronicallyenlarged and inflamed thyroids. Hashimoto called the condition "strauma lymphomatosa".There is an increased incidence of lymphoma and differentiated thyroid cancer inHashimoto's. A recent publication(Thyroid2008 18:7;729-733)has shown a suprisingly high incidence of thyroid cancer in patients who were operated on(35.6% in unsuspected cases). Most patients will never need surgery but the underlyingrisk of thyroid cancer most not be ignored and all patients with Hashimoto's shouldbe advised to have a yearly examination by their physician.The condition is not limited to humans, butoccurs spontaneously in obesechickens and beagles. In humans Hashimoto's thyroiditis can be associated with patches of white depigmented skin.
Hashimoto'sis the most common cause of a low thyroid state (hypothyroidism). It is six times more common in women than men and presents with all the symptoms of hypothyroidism. It may be associated with other endocrine organ deficiencies such as diabetes mellitus or Addison's disease (Schmidt's syndrome), Down's and Turner's syndrome.
A cytological slide of Hashimoto's thyroiditis - click to enlarge
Patients have a rubbery feeling thyroid and the thyroid function tests confirm hypothyroidism. The patients feel tired or may have no symptoms at all.
In severe cases of hypothyroidism due to Hashimoto's there are 5 classical groups of symptoms
#1.The heart is slowed (bradycardia) with enlargement of the heart and a possible collection of fluid around the heart (pericardial effusion). The ECG may show a low voltage pattern.
#2. The nervous system can be severely affected. The symptoms will range from muscle weakness and cramps to ataxia of the feet due to changes in the cerebellum of the brain. Psychiatric features are common and range from mild depression to severe psychosis. Richard Asher, the father of the English actress Jane Asher, coined the termed "Myxoedema Madness" to describe patients with severe mental disease due to hypothyroidism. A rare neurological presentation is"Hashimoto's encephalopathy" - this consists of fits and stroke-like features; these patients respond to a combination of careful thyroid replacement and steroids. Interestingly when demented patients are studied, their incidence of hypothyroidism is low ranging from 1.5% to 4.2%.
#3.The body soft tissues become very abnormal. There is often hair loss (alopecia) and the skin becomes dry and flaky. In very cases there may be collections of fluid in the body cavities (pleural, pericardial or peritoneal effusions).
#4.The reproductive function may be affected in both males and females. Women may be infertile and have heavy periods (menorrhagia) while lack of libido is common in males.
#5. The thyroid may become grossly enlarged and painful but usually gets smaller with thyroxine replacement rarely is surgery necessary.
Investigations
The serum TSH is elevated and in early cases the serum free-T4 may be normal but as the disease progresses will fall. In hypothyroidism due to Hashimoto's thyroiditis the thyroid antibodies both to thyroglobulin and thyroid peroxidase are grossly abnormal.The thyroid scan shows an irregular patchy uptake.
The condition is potentially premalignant and has an increased incidenceof thyroid cancer. As stated above the recent publication in the July 2008 issue of the Thyroid Journal (Thyroid Volume 18 number 2008) suggests that any suspicious nodules should be biopsied to exclude the very development oflymphoma. Despite hypothyroidism due to Hashimoto's thyroiditis being quite common (1%) in the adult population, clinical lymphoma of the thyroid is very rare. The prevalence of hypothyroidism is highest in elderly females, but can occur at any age and in either sex. Treatment is with with thyroid replacement. The thyroid swelling usually regresses on thyroid medication and the reduction in size may be rapid and spectacular. Surgery is very rarely indicated for uncomplicated Hashimoto's thyroiditis but may be necessary for pressure symptoms or to exclude lymphoma.