A17 yeans old girl w ho was evaluated for short height was found to have an enlarged pituitary gland. Her T4 was low and TSH was increased. Which of the follow ing is the most likely diagnosis?

Ans. is 'd' i.e., Primary hypothyroidism o Increased TSH with low thyroid hormone suggests the diagnosis of primary hypothyroidism. o Hashimotos thyroiditis is an autoimmune disorder affecting the thyroid gland and causes primaryt hypothyroidism.o Secondary hypothyroidismo It refers to thyroid hormone deficiency due to disorder of the pituitary, hypothalmus or hypothalmic pituitary portal circulation.o There is no defect in the thyroid gland per se but the hypothalmus and pituitary does not produce adequate TSH to stimulate the thyroid gland thus the thyroid is unable to secrete enough T3 & T4o In case of secondary' hyothyroidism the TSH level remians low despite decreased T3. & T4Normally any decrease in T3, T4 level leads to compensatory increase in TSH due to the negative feed back.But in secondary hypothyroidism the negative feed back is lost due to defect in pituitary or hypothalamus.Primary hypothyroidismPrimary hypothyroidism is caused due to defect in the thyroid gland per se.In these cases thyroid gland is not able to synthesize hormone despite adequate stimulation by TSH.# In fact there is compensator increase in TSH secretion by the pituitary, but still the T3, T4 level is not in the normal range.Suspected Hypothyroidism|Obtain TSH and Free T4 1||TSH highfree T4 lowTSH normalor low free T4 low||PrimaryhypothyroidismSecondaryhypothyroidism||Thyroid gland fails to produceT3 and T4. andthere is compensatory increase inTSH due to reduction in thenegative feedbackOccurs due to defect inHypothalamus or pituitary||HypothalmicPituitary|||Autoimmune hypothyroidismHashimoto's atrophicDue to defective TRH secretionby hypothalamusdue to defectiveTSH secretionby pituitaryIatrogenic:||131treament, subtotal or total thyroidectomy External irradia-tion of neck for lymphomao Tumouro Traumao Infiltrative disordero Idiopathico Tumourso Pituitary surgeryo Infiltrative disordero Sheehans syndromeo Traumao Genetic from of combind pituitary' hormone deficiencyDrugs:Iodine excess (iodine contract media and amiodarone) lithium, antithyroid drugs, paminosalicylic acid interferon a and other cytokines, amniogluthimide sunitinibCongenital hypothyroidism:Absent or ectopic thyroid dyshor mogenesis, TSH-R mutation iodine deficiencyInfiltrative disorders:Amyloidosis, Sacroidosis, hemochromatosis, scleroderma, cystinosis, ReideFs thyroiditis Overexpression of type 3 iodinase