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                        Hypothyroidism classification

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[Up] [Hypothyroidism classification] [Risk factors] [Clinical features] [End organ impact] [Associated illnesses] [Diagnosis] [Treatment] [Dose titration] [Drug interactions] [Monitoring & follow up] [Myxedema coma]

 

 

  Hypothyroidism can be classified on the basis of 

  • Etiology, 

  • Age of onset and on the basis of its 

  • Severity.                                                                        

 

Aetiology

Hypothyroidism can be classified on the basis of aetiology as 

  • Primary, 

  • Secondary or 

  • Transient. 

 

Primary Hypothyroidism

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This is hypothyroidism caused by disorders of the thyroid gland itself. 

 Causes

  1. Destruction of thyroid tissue

  • Chronic autoimmune thyroiditis -goitrous -atrophic -

  • Post thyroidectomy 

  • Post radioactive Iodine therapy for thyrotoxicosis

  • Neck radiation .

  1. Iodine deficiency .

  2. Disorders of hormone synthesis-enzyme defects .

  3. Antithyroid agents, lithium, iodine, radiocon- trast dyes containing iodine, amiodarone

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The commonest cause of primary hypothyroidism in iodine-sufficient areas is chronic autoimmune thyroiditis and in iodine-deficient areas -iodine deficiency itself.

 

 Central / Secondary Hypothyroidism

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Decreased thyroid hormone production and secretion by the thyroid gland due to inadequate stimulation by thyroid stimulating hormone (TSH) because of pituitary or hypothalamic disorders.

Causes

  1. Pituitary disorders -decreased TSH

  2. Hypothalamic disorders-decreased Thyrotropin Releasing Hormone (TRH)

  Transient Hypothyroidism
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In this type, there is decreased thyroid hormone production and secretion for a transient period of time.

Causes

  1. Silent thyroiditis -

  2. Postpartum thyroiditis 

  3. Sub acute thyroiditis 

  4. After withdrawal of thyroid hormone therapy in euthyroid patients 

Age of Onset

Hypothyroidism is also classified on the basis of age of onset as -

  1. Congenital hypothyroidism 

  2. Cretinism 

  3. Juvenile hypothyroidism 

  4. Adolescent hypothyroidism 

  5. Adult hypothyroidism.

 

 Congenital hypothyroidism

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presents at birth. It may be transient or permanent.

 

 

                    Transient

                 Permanent

  • Iodine deficiency

  • Iatrogenic

  • Maternal / Neonatal

  • Iodine deficiency. Maternal RAI therapy

  • TSH receptor blocking antibodies

  • Idiopathic

  • Thyroid dysgenesis.

  • Maternal exposure to I-131

  • Dyshormogenesis.

  • Congenital Toxoplasmosis.

  • Hypothalamic, Pituitary disorders.

 

 Cretinism

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Severe iodine deficiency causing hypothyroidism in infancy and, 

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Presenting as mental retardation, neurological mal-development and impaired growth   is called cretinism.

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The infant having this form of hypothyroidism is called a cretin. 

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It is rightly stated about a cretin that "What was supposed to be made into the image of God has turned into an Imp"

 

 Epidemiology

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It is associated with endemic goiter and severe iodine deficiency.

 

 Clinical manifestations

These consist of mental deficiency, together with either of the following:

  1. Predominant neurological syndrome. -which consists of disorders of stance and gait and disorders of hearing and speech.

  2. Predominant hypothyroidism and stunted growth 

 Prevention

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 Prevention of endemic cretinism with adequate correction of iodine deficiency.

 

 Juvenile Hypothyroidism 

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Occurs in childhood and 

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Manifests mainly as growth retardation along with other generalized features of hypothyroidism 

 

 Adolescent Hypothyroidism

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Hypothyroidism during adolescence presents with delayed puberty with/without short stature and menstrual irregularities in females.

 

 Severity 

 Hypothyroidism is also classified on the basis of severity as:

  1. Sub clinical hypothyroidism

  2. Overt or frank hypothyroidism

 

 Sub clinical Hypothyroidism

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In this, patients are asymptomatic and are identified in screening especially in patients at risk. 

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Spontaneous sub clinical hypothyroidism is more common in women and the incidence increases with age and is associated with the presence of antithyroid antibodies.

 

 Overt or Frank Hypothyroidism

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All causes of hypothyroidism can manifest with moderate to severe symptoms and signs.

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However, the clinical manifestations are variable and sometimes nonspecific too.

 

 

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