New guidelines on investigating thyroid dysfunction.

Equipment for all seasons. (Dr. Noorali Bharwani)
Equipment for all seasons. (Dr. Noorali Bharwani)

The thyroid gland produces hormone called thyroxine. The gland is in the front of the neck, below Adam’s apple, consisting of two lobes (left and right) connected by an isthmus.

In fact, the thyroid gland secretes three hormones: the two thyroid hormones, thyroxine (T4) and triiodothyronine (T3); and calcitonin.

The thyroid hormones influence the metabolic rate and protein synthesis, and in children, growth and development. Calcitonin is involved in helping to regulate levels of calcium and phosphate in the blood.

Many things can go wrong with the thyroid gland. Examples of thyroid disorders include hyperthyroidism (increased activity), hypothyroidism (reduced activity), thyroid inflammation (thyroiditis), thyroid enlargement (goitre), thyroid nodules, and thyroid cancer.

In iodine-sufficient regions, the most common cause of hypothyroidism is the autoimmune disorder Hashimoto’s thyroiditis.

Most adults who go for regular annual physical examination get tested for thyroid function. Is this necessary?

The Canadian Task Force on Preventive Health Care (CMAJ November 18, 2019) strongly recommends against screening for thyroid dysfunction in asymptomatic nonpregnant adults. Why? Guidelines say, “Treating asymptomatic adults for screen-detected hypothyroidism may result in little to no difference in clinical outcomes.”

These recommendations do not apply to patients with previously diagnosed thyroid disease or thyroid surgery; exposure to medications known to affect thyroid function; exposure to thyroid radioiodine therapy, or radiotherapy to the head or neck area; or pituitary or hypothalamic diseases.

Guidelines suggest clinicians should remain alert to signs and symptoms suggestive of thyroid dysfunction and investigate accordingly. This is not always easy. The signs and symptoms of thyroid dysfunction are variable between patients and often nonspecific.

Symptoms of hypothyroidism may include tiredness, sensitivity to cold, dry skin, hair loss, weight gain and slowed movements and thoughts. If left untreated, hypothyroidism may increase the risk of cardiac dysfunction, hypertension, dyslipidemia, cognitive impairment and, in rare cases, myxedema coma.

If the thyroid is overactive (hyperthyroidism), symptoms may include regular rapid heartbeat (sinus tachycardia), atrial fibrillation, hyperactivity or irritability, intolerance to heat, tremor and weight loss.

Some people with thyroid dysfunction have no symptoms.

Thyroid dysfunction is diagnosed based on abnormal levels of serum thyroid-stimulating hormone (TSH) and can be characterized as either hypo- or hyperthyroidism.

Minor variations in thyroid function as measured by abnormal levels of TSH are often self-limiting. Observational studies have reported that levels of TSH appear to revert to normal without treatment in 37 to 62 per cent of patients with initially elevated levels and 51 per cent with initially low levels, particularly for milder cases of thyroid dysfunction (mean follow-up 32–60 months).

Summary of recommendation for clinicians, policy-makers and patients

The guidelines recommend against screening asymptomatic nonpregnant adults aged 18 years and older for thyroid dysfunction in primary care settings.

Screening results in overuse of resources without a demonstrated benefit.

These recommendations do not apply to patients with previously diagnosed thyroid disease or thyroid surgery; exposure to medications known to affect thyroid function (e.g., lithium, amiodarone); exposure to thyroid radioiodine therapy, or radiotherapy to the head or neck area; or pituitary or hypothalamic diseases.

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