Hypothyroidism can be classified on the basis of
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Etiology,
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Age of onset and on the basis of its
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Severity.
Aetiology
Hypothyroidism can be classified on the basis of aetiology as
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Primary,
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Secondary or
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Transient.
Primary Hypothyroidism
 | This is hypothyroidism caused by disorders of the thyroid gland itself. |
Causes
Destruction of thyroid tissue
Chronic autoimmune thyroiditis -goitrous -atrophic -
Post thyroidectomy
Post radioactive Iodine therapy for thyrotoxicosis
Neck radiation .
Iodine deficiency .
Disorders of hormone synthesis-enzyme defects .
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
Pituitary disorders -decreased TSH
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
Silent thyroiditis -
Postpartum thyroiditis
Sub acute thyroiditis
After withdrawal of thyroid hormone therapy in euthyroid patients
Age of Onset
Hypothyroidism is also classified on the basis of age of onset as -
Congenital hypothyroidism
Cretinism
Juvenile hypothyroidism
Adolescent hypothyroidism
Adult hypothyroidism.
Congenital hypothyroidism
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presents at birth. It may be transient or permanent. |
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Transient |
Permanent |
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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:
Predominant neurological syndrome. -which consists of disorders of stance and gait and disorders of hearing and speech.
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:
Sub clinical hypothyroidism
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. |