Congenital hypothyroidism (Cretinism)

What is Congenital hypothyroidism?

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Congenital hypothyroidism is a disease of the thyroid gland; this is an endocrine gland located in the anterior neck.The main hormones secreted by the thyroid gland are mostly thyroxine (T4), and a small amount of triiodothyronine (T3). Thyroid hormones have wide-ranging effects on metabolism affecting most organ systems in the body.The secretion of thyroid hormones is stimulated by thyrotrophin (TSH) which is secreted from the pituitary gland, which is in turn secreted in response to thyrotrophin releasing hormone (TRH), secreted by the hypothalamus.Hypothyroidism refers to an underactive thyroid gland - meaning inappropriately low secretion of thyroid hormones - T4 and T3. It can occur in the newborn (congenital) or in a previously normal adult (acquired).Hypothyroidism in the newborn may result from absence of or abnormal development of the thyroid gland, destruction of the thyroid gland, failure of stimulation of the thyroid by the pituitary, and/or by defective or abnormal synthesis of thyroid hormones.

Statistics on Congenital hypothyroidism?

Incomplete development of the thyroid is the most common defect and occurs at a rate of 1 out of every 3,000 births. Girls are twice as often affected than boys.

Risk Factors for Congenital hypothyroidism

Numerous causes:

Numerous genetic syndromes

Underactive pituitary gland (secondary) eg due to a pituitary tumour or the absence of the pituitary gland

Trauma

In most cases no underlying cause of the deficiency is found.

Progression of Congenital hypothyroidism

If untreated, even mild hypothyroidism can lead to severe mental retardation and growth retardation. Development is delayed early on, often indicated by failure to meet normal milestones. The appearance of teeth may be delayed. These problems become more severe as the child ages. Growth failure in terms of body length is noted very early.

How is Congenital hypothyroidism Diagnosed?

Routine screening of the newborn using a blood-spot, as in the Guthrie test, to detect a high TSH level as an indicator of primary hypothyroidism is efficient and cost-effective, usually done at 5-7 days; cretinism is prevented if T4 is started within the first few months of life.

Prognosis of Congenital hypothyroidism

Very early diagnosis generally results in a good outcome for the infant, in terms of growth and mental capability. Newborns diagnosed and treated in the first month to month and a half generally develop normal intelligence. Absence of thyroid hormone during early life gives a poor outlook in terms of mental development.

How is Congenital hypothyroidism Treated?

Early diagnosis is imperative. Most of the effects of hypothyroidism are easily reversible. However, critical development of the nervous system takes place in the first few months after birth. Thyroid hormone deficiency may result in irreversible damage to the nervous system with marked mental retardation.

Replacement therapy with thyroxine is the standard approach to treatment of hypothyroidism. Once medication starts, the blood levels of TSH and free T4 are monitored to keep the values within a normal range.

Absence of the thyroid and defective thyroxine production are not preventable. Destruction of the thyroid in the fetus may occur if the mother is treated with radioactive iodine for thyroid cancer while she is pregnant. Infants of mothers taking antithyroid medications should be observed carefully after birth for evidence of drug induced transient (brief) hypothyroidism.

Congenital hypothyroidism References

[1] Congenital hypothyroidism as retrieved from www.nlm.nih.gov on 23/12/2003[2] Hypothyroidism as retrieved from www.kumarandclark.com on 23/12/2003[3] Longmore M, Wilkinson I, Torok E. OXFORD HANDBOOK OF CLINICAL MEDICINE. Oxford Universtiy Press. 2001[4] Robbins, S.L., Cotran, R.S., Kumar, V. Robbins Pathologic Basis of Disease 5th ed. W.B. Saunders 1995.