What Is Cretinism?

Cretinism Definition

The term cretin was derived from the French word chrétien, literally meaning “Christian” or “Christ like” as the diseased were mentally retarded and incapable of doing sin. It is the Iodine deficiency disorder associated with insufficient thyroid hormone activity occurs during fetal, infant or childhood phases.

  • In children, hypothyroidism produces mental and physical retardation, known as cretinism
  • The TBG(Thyroxine binding globulin) may be elevated due to maternal hyperestrogenism and therefore total T4 (thyroxine or tetraiodothyronine) and T3 (triiodothyronine)may be normal.
  • The lack of feedback will also give an elevated TSH level. Prompt diagnosis and treatment are important in cretinism since any delay in initial replacement may lead to irreversible damage.
  • Maternal hypothyroidism may also cause neonatal cretinism. Hypothyroidism may result from treatment of hyperthyroidism using antithyroid drugs or radioactive iodine.
  • Replacement of the hormone will produce an immediate effect.

It is either due to the breakdown of thyroid development or a deficit in hormone synthesis (sporadic cretinism) or because of extreme iodine deficiency (endemic cretinism). It is typically distinguished through infancy or childhood, however, the best preventive strategy is the screening of neonates. Everyday treatment with thyroxine (8-12 ug/kg) should be initiated as early as possible as mental retardation that has ensued already is only partially reversible. The response is climactic: physical development and growth are revived and additional mental retardation is checked.

This case represents the foremost severe sort of untreated congenital hypothyroidism presenting as myxedematous cretinism along side slowness.

About Thyroid Gland and Thyroid Hormone

  • Thyroid gland is one of the important endocrine glands of our body and present in the neck region. It synthesizes and secretes thyroid hormones such as triiodothyronine (T3) and tetraiodothyronine (T4). Inside the follicular cells of the gland, these hormones are synthesized by iodinating tyrosine residues at various positions in the glycoprotein called thyroglobulin.
  • So, Iodine plays a critical role in the synthesis of thyroid hormones.
  • In general, Thyroid hormone plays a vital role in maintaining basal metabolic rate, oxidation food stuffs and growth and development at an early stage of life.

Synthesis of Thyroid Hormone

Synthesis of Thyroid hormone

Steps in Thyroid Hormone Synthesis and Secretion

  • Step 1: Synthesis of Thyroglobulin in follicular cells and release into the follicular lumen.
  • Step 2: Transport of Iodide (anionic form) into follicular cell by active transport and moves to follicular lumen by facilitated diffusion. This process is called Iodide trap.
  • Step 3: Oxidation of Iodide into Iodine takes place in border of follicular cells.
  • Step 4: Attachment of Iodine with Thyrosine which is catalyzed by the enzyme peroxidase to form (Monoiodotyrosine ) MIT and (Diiodotyrosine) DIT.
  • Step 5: Linking of iodinated tyrosines together to form T3 and T4.
  • Step 6: Endocytosis of thyroglobulin colloid.
  • Step 7: Cleavage of T4 and T3 from thyroglobulin by lysosomal enzymes and release of hormones from the follicular cell into the blood.

Types of Cretinism

Cretinism is of 2 types:

Congenital Cretinism

  • Incidence is 1:3000 to 1:4000 in an iodine-deficient endemic area.
  • It can be caused due to a defect in the genes encoding various enzymes involved in thyroid hormone synthesis such as thyroglobulin, iodotyrosine deiodinase and also thyroid-stimulating hormone (TSH). This type of hypothyroidism is also called congenital hypothyroidism, non-goitrous (CHNG).
  • There are at least 5 types of CHNG due to mutation of five different genes namely CHNG1 to CHNG5.
  • Non Goitrous congenital hypothyroidism is considered as the most prevalent inborn endocrine disorder.

Endemic Cretinism

  • For adults, the normal recommended dietary intake of iodine is 150ug / day.
  • This type of cretinism often occurs in children who live in the geographical settings where iodine is deficient and it is not corrected by either supplementing iodine or thyroid hormone to regain normal thyroid hormone levels during early life.
  • Mostly, the mother of endemic cretinism children have had affected with hypothyroidism during pregnancy (Maternal hypothyroidism).
  • Exposure to radioactive Iodine during pregnancy may also be the cause in some cases.
  • Use of antithyroid drugs or sulfonamides during pregnancy.
  • Iodine intake as low as 25 mcg/day during pregnancy would be a potential risk factor for giving birth to cretinism neonates.

Neurological cretinism – It is characterized by the following conditions:

  • Retarded growth
  • Deaf-mutism
  • Motor spasticity
  • Severe mental retardation with squint

Myxedematous cretinism– It is characterized by the following conditions:

  • Retarded growth
  • Incomplete maturation of facial expression
  • Thickened and dry skin
  • Small and dry hair, eyelashes and eyebrows
  • Mental retardation of comparatively lesser intensity to neurological cretinism
  • Delayed sexual maturation
  • Other clinical manifestations of hypothyroidism

Cretinism Causes

There are two main reasons for cretinism:

  • Lack of thyroid gland and failure of the thyroid gland to produce thyroid hormone (congenital cretinism or congenital iodine deficiency syndrome).
  • Iodine deficiency in diet (Endemic cretinism).

Pathophysiology

  • Optimal level of maternal thyroid status is essential for normal growth of the fetus. It is the maternal thyroid hormone, the only source for fetus that crosses placenta for fetal brain development.
  • Thyroid hormone is essential for growth, branching and myelination of neuronal cells of CNS at fetal and neonatal stage. So, absence of thyroid hormone at these stages would severely affect the generalized nervous system development.
  • Thyroid hormone also plays a critical role in skeletal muscle development than soft tissue development. During cretinism, this disproportionate rate of growth leads to excessive growth of soft tissue compared to skeletal tissues.

 Cretinism Clinical Features

  • Generally characterized by shunted growth and mental retardation.
  • Short stature (Dwarfism).
  • Mild neurological impairment with reduced muscle tone and coordination.
  • Hearing and speech defects.
  • Unable to maintain posture and balance with characteristic walking style.
  • Myxoedema.
  • Enlargement of Thyroid gland (Goitre).
  • Sparseness of hair and nails.
  • Voice will be deep and hoarse voice.
  • Retardation of sexual attributes.
  • Thickened skin.
  • Enlarged tongue.
  • Protruded abdomen.
  • Umbilical hernia
  • Delayed tendon reflexes.
  • Decreased Intelligent quotient (IQ).

Diagnosis of Cretinism

  • Congenital cretinism with severe hypothyroidism can be identified by antenatal screening test in the first month of life.
  • Technetium (Tc– 99m pertechnetate) thyroid scan.
  • Radioactive Iodine (RAIU) test (to make differentiate between congenital absence or a defect in organification process).
  • Post natal – Blood spot test such as Guthrie’s test.
  • Elevated serum Thyroid binding globulin (TBG) and TSH level.
  • Elevated serum T3 and low T4 level.

Treatment of Cretinism

  • Once diagnosed, treatment should be started within 1 -2 weeks of life.
  • Treatment should be started before the onset of symptoms, if developmental abnormalities and mental retardation starts to appear, will not reverse even on thyroid hormone replacement therapy.
  • Recommended dose is 10 to 15ug per kg body weight. The dose should be increased as the age progresses.

Question and Answers:

Q 1. Write about causes of Endemic cretinism.

Answer:

  • Dietary Iodine deficiency
  • Failure of responding to Iodine of thyroid hormone supplement.
  • Maternal Hypothyroidism.
  • Exposure to radioactive Iodine during pregnancy
  • Use of antithyroid drugs or sulfonamides during pregnancy

Q 2. What are the main symptoms of cretinism?

Answer:

  • Generally characterized by shunted growth and mental retardation.
  • Short stature (Dwarfism).
  • Mild neurological impairment with reduced muscle tone and coordination.
  • Hearing and speech defects.
  • Unable to maintain posture and balance with characteristic walking style.
  • Myxoedema.
  • Enlargement of Thyroid gland (Goitre).

Q 3. What are the characteristics of cretinism?

Answer: The 3 characteristic options of neurologic endemic hypothyroidism in its absolutely developed type are very severe moronity along side squint, deaf-muteness, and motor fitfulness with disorders of the arms and legs of a characteristic nature.

Q 4. Can goiter develop into cancer?

Answer: Goiter are often the results of thyroid tumours, that are sometimes benign, however generally malignant. Most thyroid tumours occur as separate nodules, however there are many styles of thyroid cancer which will cause generalized swelling of the secretor.

Stay tuned with BYJU’S for more on cretinism and associated conditions.

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