Hypothyroidism: What every patient needs to know
- Part 1 -

Dr Y Premchandra Singh *

Häggström, Mikael. "Medical gallery of Mikael Häggström 2014". Wikiversity Journal of Medicine 1 (2). DOI:10.15347/wjm/2014.008. ISSN 20018762. :: Pix - Wikipedia

Hypothyroidism has been described in some form in the medical literature since 1871

It is traditionally defined as resulting "from reduced effects of thyroid hormone on tissues"

A. Epidemiology Primary hypothyroidism is a very prevalent disease worldwide. In the US it is estimated to be 1 to 2 % and this rate increases with age, rising to approximately 10% in adults over 65. The prevalence of biochemical hypothyroidism is 4.6 % that of clinical hypothyroidism is 0.3 %. Congenital hypothyroidism, one of the most common congenital diseases, has an incidence of 1/4000 newborns. Hormone resistance syndromes and central hypothyroidism is rare .In the UK the prevalence of hypothyroidism is estimated at 2% and has been found to be 5-10 times more common in women, especially with small body size at birth and during childhood. The incidence varies with iodine status of the population.

Why is thyroid disease on the rise ? Doctors are a puzzled lot because the reasons are yet to be ascertained. Strangely, it has increased more among women in the 20-40 age group. In India for the past five to seven years, we have been seeing a fourfold increase in hypothyroidism. And it is more in women. It is an autoimmune disorder like diabetes and it is believed not to be due to lifestyle-related problems. In some cases, it is a genetic problem. Many experts have opined that it could be linked to more number of diabetes cases these days.

Special Issue on Indian Thyroid Guidelines 2011, JAPI published that thyroid disease is being increasingly diagnosed with greater awareness and is one of the chronic non-communicable diseases affecting women more though male population is not spared of the ailment. In India thyroid disorders are in a transition zone from a predominant iodine deficient nation to now a iodine sufficient population. The global goiter prevalence is more than 2 billion with more than 40 million in India. The true prevalence and incidence in India of Thyroid disorders is difficult to estimate, even conservative estimates put the geographical prevalence between 42 million cases of Iodine Deficiency Disease is included.

Functional studies of the goitrous subjects showed overall prevalence of 5.4% hypothyroidism, 1.9% hyperthyroidism. 7.5% prevalence of autoimmune thyroiditis was demonstrable by fine needle aspiration biopsy among female goitrous students. On the basis of this countrywide study and other related studies, it can now be estimated that the total burden of significant thyroid disease in the country in the post salt-iodization phase is approximately 42 million.

As India is now predominantly Iodine sufficient we are nearing the peak prevalence of the autoimmune epidemic. It is estimated that about 200 million people are at the risk of Iodine Deficiency Disease in our country.

The role of Iodine as an immunogen in prevalence of autoimmune thyroid disorders in India is a contentious issue. Despite the National Iodine Deficiency Disorder Control Programme (NIDDCP) since 1962, many districts in India still have pockets of Iodine deficiency.

Iodine is an essential micronutrient with an average daily requirement at 100-150 micrograms for normal human growth and development. Deficiency of Iodine can cause physical and mental retardation, cretinism, abortions, stillbirth, deaf mutism, squint and various types of goitre.

B. Causes of hypothyroidism : Iodine deficiency is the most common cause of hypothyroidism worldwide. In iodine-replete individuals hypothyroidism is frequently caused by Hashimoto's thyroiditis, or otherwise as a result of either an absent thyroid gland or a deficiency in stimulating hormones from the hypothalamus or pituitary. Exposure to iodine 131 from nuclear fallout, which is chemically indistinguishable from nonradioactive isotopes and taken up by the thyroid gland with them, destroys thyroid cells and increases the risk of hypothyroidism.

Congenital hypothyroidism is very rare, accounting for approximately 0.2% of cases, and can have several causes such as thyroid aplasia or defects in the hormone metabolism. Thyroid hormone insensitivity (most often T3 receptor defect) also falls into this category, although in this condition levels of thyroid hormones may be normal or even markedly elevated.

Hypothyroidism can result from post partum thyroiditis up to 9 months after giving birth, characterized by transient hyperthyroidism followed by transient hypothyroidism.

Hypothyroidism can result from de Quervain's thyroiditis, which, in turn, is often caused by having bad case of flu that infects and destroys part, or all, of the thyroid. Hypothyroidism can also result from sporadic inheritance, sometimes autosomal recessive. Temporary hypothyroidism can be due to the Wolff Chaikoff effect. Hypothyroidism can be caused by lithium-based mood stabilizers, usually used to treat bipolar disorder (previously known as manic depression). In fact, lithium has occasionally been used to treat hyperthyroidism.

C. Symptoms : Clinical features are variable, depending on the age at onset, and severity/duration of the deficiency. Cold intolerance, fatigue, dryskin, parasthesias, weight gain, menstrual irregularity, constipation, depression, pubertal delay, arthralgias, cognitive dysfunction, hearing difficulty, cramping and myalgias.

D. Signs : Classical description are coarse skin, periorbital puffiness, delayed relaxation of tendon reflexes, hoarseness of voice, bradycardia, Carotenaemia, Galactorrhea, periorbital edema, as well as slow movement and speech.

Many symptoms of hypothyroidism are nonspecific, especially in early disease. Clinical scoring systems have been devised to predict the likelihood of the disease. The Billewicz score is an older scoring system. Scores can range from + 67 to–47, with the highest weightage given to a sluggish ankle jerk and slow movements.

A newer scoring system takes into account recent advances in laboratory tests of thyroid function

How is Hypothyroidism diagnosed ? Hypothyroidism is usually suspected because certain symptoms are present. The diagnosis is confirmed by blood testing.

In most circumstances, the TSH is the most sensitive marker of your body's thyroid status. In Hypothyroidism the TSH rises, as the pituitary gland tries to signal the thyroid gland to release more thyroid hormone. The T4 levels may be low or normal. The T3 levels are not helpful to diagnose Hypothyroidism, and therefore are not usually measured.

In rare situations where the cause of the Hypothyroidism is a pituitary problem, the TSH level may be normal or low.

In these cases the diagnosis is based on a low T4 value and a low or normal TSH.

Antibodies against the thyroid gland may be detected in the blood if the hypothyroidism is caused by the body's immune system

(To be contd)