Disorders of Thyroid

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Disorders of thyroid parathyroid glands

• M.Prasad Naidu
• MSc Medical Biochemistry,
• Ph.D.Research Scholar

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Disorders of thyroid parathyroid glands

• 1. Hyperthyroidism
• 2. Thyroid Adenoma
• 3. Graves disease

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Hyperthyroidism

• Causes
• Due to the presence of TSH like substances
  proved by RIA studies
• The conc of TSH was found to be 0/less in plasma
  of Hyperthyroidism patients
• The TSH like substances are Abs which bind with
  same membrane receptors of TSH
• These substances activate c-AMP system ?T4
• These Abs act for long time (12hrs) (TSH-1hr)
• The ? of high T4 caused by Abs suppresses TSH
  production
• Usually these Abs are developed b/cos autoimmunity

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Thyroid Adenoma

• Some times localised tumor develops in Thyroid
  tissue called Thyroidadenoma
• TA secretes large quantities of T4T3
• It is not associated with autoimmunity
• As far as this adenoma remains active, the other
  parts of Thyroid gland will not secrete the
  hormone.
• This is b/cos the hormone from Adenoma ?
  depresses the production of TSH

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Graves disease

• Autoimmune disease
• Normally TSH combines with surface receptors of
  thyroid cells ? syn of T4
• But in GD , the TSH autoAbs (B-TSAB) produced by
  B-lymphocytes (Plasma cells) activate the
  TSH-receptors ? secretion of T4

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Symptoms of Hyperthyroidism

• Intolerance to heat ( due to ? BMR)
• ? sweating ( due to vasodialation)
• ? body wt ( Fat metabolism)
• ? motility of GIT ? diarrhoea
• Muscular weakness ? ?protein catabolism
• Nervousness, extreme fatigue, inability to sleep,
  mild tremor in the hands, psychoneurotic symptoms
  such as extreme anxiety/worry (stimulation of
  CNS)
• Enlargement of Thyroid gland? i.e, Toxic goiter
• Exophthalmos Autoimmune
• some degree of protrusion of eye balls if
  severe blindness develops due to
• i)protrusion of eye ball stretches the optic
  nerve
• Ii) eye lids cannot be closed ? dry ? infection

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hypothyroidism

• ? secretion of Thyroid hormones
• Autoimmune disease which causes destruction of
  Gland
• In most patients it starts as the glandular
  inflammation called Thyroiditis
• Thyroiditis ? fibrosis of the gland
• Hypothyroiditis? Myxedema (adults) Cretinism
  (Children)

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Myxedema

• Due to hypothyroidism in adults
• Causes occurs in severe conditions complete
  lack of thyroid hormones
• Signs symptoms
• Swelling of the face
• Bagginess under the eyes
• Non-pitting type of edema- when pressed it does
  not make pits and the edema is hard (accumulation
  of Procho.SO4 which form hard tissue with ?
  accumulation of fluid)
• Atherosclerosis ? cholesterol blood ? bp

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Myxedema

• Other general symptoms
• Fatigue muscular sluggishness
• Extreme somnolence ( 14-16 hrs/day)
• Menorrhagia polymenorrhea
• ? Cordiovascular functions such as ?heart rate, ?
  force of contraction of heart ? crodiac out put ,
  ? blood volume
• ?Body wt
• Constipation
• Mental sluggishness
• ? hair growth
• Scaliness of the skin
• Frog like husky voice

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Cretinism

• Children
• Causes congenital absence of thyroid gland
  (genetic disorder or lack of I2 in diet)
• Features
• The newborn baby may appear normal at birth (due
  to supply of T4 from mother)
• But after few weeks starts developing sluggish
  movements croacking sound while crying ? mentally
  retarded
• Skeletal growth is more affected than soft
  tissues
• Tongue becomes so big affects swallowing
  breathing
• Stunted growth

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Differences b/n Cretinism Dwarfism
CRETINISM DWARFISM
Mental retardation Development of Nervous system is normal
Diff parts of the body are disaapropriate Proportionate
Reproduction system is affected normal
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Goiter

• Enlargement of thyroid gland
• Occurs both in hypothyroidism Hyperthyroidism
• Goiter in Hyperthyroidism ? Toxic Goiter
• Due to tumor of the gland Size ? - ? number of
  hormones secreting cells ? hormone level
  Toxic Goiter
• Goiter in hypothyroidism non toxic Goiter
• Only enlargement of gland hormone secretion is ?

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Goiter

• Based on the cause, Non-toxic Goiter is of 2
  types
• i) Endemic Colloid Goiter-
• Due to lack of I2 I2 intake lt50µg/day
• Therefore no formation of hormones
• By feed back mechanism, hypothalamus and anterior
  pituitary are stimulated
• This ? secretion of TRH and TSH ? secretion of
  TGb? Follicles
• As there are no hormones to be cleaved, ?
  accumulation in the follicles
• Therefore ? size of the gland
• In Swiss, Alps, Andes, Great region of US and in
  India Kashmir Valley? Soil does not I2?
• Therefore Food stuffs lack I2 very common
  before the introduction of iodized salts

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Idiopathic Non-toxic Goiter

• Enlargement of Thyroid gland occurs even without
  I2 deficiency
• Exact cause not known
• These patients are first affected by Thyroiditis
  which reduce synthesis of Thyroid hormones
• Therefore secretion of TSH ?
• ? Size of the gland
• In some persons the abnormal enzyme system leads
  to Goiter(due to deficiency of enzymes like
  peroxidase, iodinase and deiodinase which are
  required synthesis of T3T4)

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Idiopathic Non-toxic Goiter

• Goitrogenic Substances ( Goitrogens)
• Eg Goitrin
• Contains antithyroid substances like
  propylthiouracil
• Therefore TSH secretion ? enlargement of Thyroid
  gland
• Goitrogens ? in turnips, cabbage, soyabeans
• The goitrogens become active only during low I2
  intake

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Treatment for Thyroid disorders

• Treatment for Hyperthyroidism-
• 1. Surgical removal Thyroidectomy
• 2. Antithyroid substances Thiocyanate,
  thiourylenes, high conc of inorganic iodides
• Treatment of hypothyroidism
• Only treatment is administration of Thyroid
  extract/ ingestion of pure thyroxine ( tablet)

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Anti thyroid substances

• Drugs which supress the secretion of T3T4
• 1. Thiocyanate the same active pump which
  transports I- into Thyroid cells, transports
  thiocyanate also
• So thiocyanate competitively inhibits I2
  transport
• I2 transport is inhibited
• ? synthesis of Thyroxine

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Thiourylenes

• Thiourea related substances
• Eg Propylthiouracil and methimazole prevent the
  formation of T4 from iodides and Tyr
• This is achieved by blocking peroxidase activity
  and partly by blocking coupling of MIT DIT
• During the use of these two antithyroid agents
  even though the synthesis of Thyroid hormone is
  inhibited , the formation of TGb is not stopped
• The deficiency of the hor ? TSH secretion ? Size
  Thyroid gland with more secretion of TGb
• TGb accumation in gland ? enlargement ? non-toxic
  G

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High conc of inorganic iodides

• All phases of Thy.activity ?
• ? release of Thyroxine
• ? Size
• ? blood supply
• Therefore iodides are frequently administrated
  to hyperthyroid patients

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Thyroid function Tests

• The most accurate diagnostic test is? Direct
  measurement of conc of Free thyroid hormones in
  the plasma (T3T4)
• Measurement of BMR-
• In Hyperthyroidism, ? 30-60
• In hypothyroidism, ? 20-40
• The measurement of TRH and TSH-
• In Hyperthyroidism? total absence of TRH TSH
  (due to ve feed back mechanism by the ?level of
  Thyroid hormones)