In hypothyroidism, as the name indicates, there is a decline in the functioning of the thyroid gland. The gland is either damaged as a result of an autoimmune disease of the thyroid gland, or in the case of an overactive thyroid gland, when more than the required amount of antithyroid drug has been administered. Similarly, hypothyroidism may occur following radio-iodine treatment or surgery, in cases of an overactive thyroid gland.

Subclinical hypothyroidism.

The most characteristic feature of an underactive thyroid gland is that it remains asymptomatic for a long period, and there are only vague symptoms in the beginning. Sometimes the diagnosis is made when a person is undergoing routine tests for a general medical check-up.

The hidden nature of the disease is clear enough. Such early cases of hypothyroidism are suspected, diagnosed/investigated and labelled under the head 'Subclinical Hypothyroidism'. They may, however, still be in the infancy stage and have only minimal symptoms. This truly highlights the need for early diagnosis and treatment of all cases of hypothyroidism.

When to suspect subclinical hypothyroidism?

The disease may be suspected when the patient feels lethargic, especially in the case of a patient suffering from hyperthyroidism who is undergoing antithyroid drug treatment, or radio-iodine therapy, or has undergone surgery of the thyroid gland. Or, the condition may occur in cases which have a positive family history of hypothyroidism.

How to diagnose subclinical hypothyroidism?

Once suspected, estimation of the thyroid-stimulating hormone (TSH) in the blood should be carried out. The levels of this test will be elevated significantly, although the levels of T4 may be just on the lower side of the normal, or just below the normal level. T3 does not playa significant! diagnostic role in the detection of hypothyroidism, and its level may be found within normal limits.

What is TSH?

It is a hormone secreted by the pituitary gland, lying in the brain, which controls the activity of the thyroid gland. This hormone has got a highly stimulating action on thyroid activity, so that as soon as the activity of the thyroid gland decreases (hypothyroidism), and the quantity of the thyroid hormone, the major being T4, or even when it touches the lower limit of its normal range, there will be an increase in the secretion of TSH from the pituitary gland.

Hence there is a close relationship between the pituitary and thyroid glands so that a normal level of thyroid hormones may be maintained in the blood as far as possible. (However, it may be said in passing, that if hypothyroidism occurs as a result of the involvement/ disease of the pituitary gland, the levels of TSH will not be elevated, although T4 may be on the lower side).

Since the raised levels of TSH the blood is the most sensitive/ earliest index for the decreased function of the thyroid gland, this test, along with T4 must be carried out whenever there is the slightest suspicion regarding the underactivity of the thyroid gland.

Does subclinical hypothyroidism require treatment?

Difficulty does arise in such cases. However, it may be said that in the absence of significant, rather troublesome symptoms, the physician will have to make his own judgement for the initiation of therapy. If no therapy is considered necessary for the time being, the patient must be monitored at least 3-6 monthly, so that the disease does not progress unnoticed.

As regards the size of the thyroid gland, in cases of hypothyroidism, it may be noted that the gland may be either enlarged or atrophied, or may remain normal in size. Hence the size of the thyroid does not indicate the activity of the gland, and, therefore, one has to depend on the levels of thyroid function tests in the blood.