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 Hypothyroidis
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This is hypothyroidism caused by disorders of the thyroid gland itself. |
Causes
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Destruction of thyroid tissue
Chronic autoimmune thyroiditis -goitrous -atrophic -
Post thyroidectomy
Post radioactive Iodine therapy for thyrotoxicosis
Neck radiation .
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Iodine deficiency .
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Disorders of hormone synthesis-enzyme defects .
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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
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Pituitary disorders -decreased TSH
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Hypothalamic disorders-decreased Thyrotropin Releasing Hormone (TRH)
Transient Hypothyroidism
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In this type, there is decreased thyroid honnone production and secretion for a transient period of time. |
Causes
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Silent thyroiditis -
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Postpartum thyroiditis
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Sub acute thyroiditis
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After withdrawal of thyroid hormone therapy in euthyroid patients
Age of Onset
Hypothyroidism is also classified on the basis of age of onset as -
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Congenital hypothyroidism
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Cretinism
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Juvenile hypothyroidism
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Adolescent hypothyroidism
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Adult hypothyroidism.
Congenital hypothyroidism
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 maldevelopment 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 goitre and severe iodine deficiency. |
Clinical manifestations
These consist of mental deficiency, together with either of the following:
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Predominant neurological syndrome. -which consists of disorders of stance and gait and disorders of hearing and speech.
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Predominant hypothyroidism and stunted growth
Prevention
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 generalised 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:
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Sub clinical hypothyroidism
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Overt or frank hypothyroidism
Subclinical 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 subclinical 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. |