HYPOTHYROIDISMDr Prabhat AgarwalAsst Prof, P.G. Dept of Medicine,S.N.M.C. Agra

IntroductionReduced production of thyroid

hormone is the central featureIt is the second most common

endocrine disorder (after diabetes mellitus) is USA

It is more common in femalesF:M ratio is approx 10:1Rates of hypothyroidism increase

dramatically with age

Risk FactorsMore common in individuals who

have a family history of thyroid disorders

Hypothyroidism and thyroid cancers are more common in individuals who have had irradiation of their neck in childhood

However, most cases occur in individuals with no risk factors

Causes

PRIMARY HYPOTHYROIDISM-Thyroiditiso Hashimoto’s throiditis (Chronic

lymphocytic)o De Quervain’s thyroiditis (Subacute

granulomatous)o Silent/Painless thyroiditis (Subacute

lymphocytic)o Reidel’s thyroiditis (Subacute

fibrocytic)

Iatrogenic causes o Radioactive iodine treatment of Grave’s dso Thyroidectomy

SECONDARY HYPOTHYROIDISM-Pituitary surgeryIntracranial radiationCongenital panhypopituitarismInfiltrative diseases like sarcoidosis,

amyloidosis, hemochromatosis

OTHERS-

Drugs like lithium, interferon, amiodaroneIodine deficiency

PRIMARY V/S SECONDARY HYPOTHYROIDISM

PRIMARY SECONDARY

SKIN Thick and without wrinkles

Thin with fine wrinkles

HAIR Coarse Fine

MENSES Menorrhagia Amenorrhea

SECONDARY SEXUAL CHARACTERS

Normal Poor

HEART SIZE May be enlarged Small

GOITRE May be present Absent

SOFT TISSUE EDEMA

Marked Absent

BLOOD PRESSURE

Normal or High Low

CHOLESTEROL

Increased Normal

TSH High Low

PRIMARY SECONDARY

PLASMA CORTISOL Normal Low

TRH STIMULATION TEST

Exaggerated Response

No response

THYROID AUTO ANTIBODIES

May be present Absent

TO DIAGNOSE PRIMARY AND SECONDARY HYPOTHYROIDISM CLINICALLY, ONE SHOULD ALWAYS EXAMINE THE SKIN, HAIR, SECONDARY SEXUAL CHARACTERISTICS AND SOFT TISSUE EDEMA

Hashimoto’s ThyroiditisMost common cause of goitrous

hypothyroidism in iodine sufficient parts of the world

Characterized by thyroidal lymphocytic infiltration with germinal centre formation, follicular damage or destruction with fibrosis

Goitre develops gradually and is firm in consistency

Presence of anti TPO and anti thyroglobulin antibodies favours the diagnosis

History of other auto immune disorders like rheumatoid arthritis, pernicious anemia, diabetes mellitus should be ascertained

Clinical FeaturesLargely due to the reduced metabolic

rate and deposition of glycosaminoglycans (GAG) in different body compartments

Myxoedema refers to the boggy appearance of the skin and subcutaneous tissues in the patients with severe hypothyroid state

Skin is pale and cool, reduction in sweat and sebaceous secretions causing dryness and coarseness

GAG deposition in the larynx and pharynx leads to hoarseness of voice

Cardiovascular involvement causes decreased cardiac output, narrowing of pulse pressure and increased systemic vascular resistance causing diastolic hypertension. Pericardial effusion may occur

Modest weight gain despite reduced appetite and constipation due to reduced gut peristalsis

In adult women, decreased libido, failure of ovulation, polymenorrhoea, menorrhagia and decreased fertility may be seen

In men, decreased libido, oligospermia and impotence may result

These are though to result because of hyperprolactinemia as prolactin is also under TRH control

A child with congenital hypothyroidism is sluggish and may present with prolonged physiological jaundice, meconeum ileus, umbilical hernia, feeding difficulties, dry scaly skin and a large tongue

Cretinism: severe hypothyroidism of infancy

X Ray Pelvis will reveal dysgenesis of the femoral capital epiphysis, which is pathognomonic of hypothyroidism in infancy and childhood

Signs and SymptomsSYMPTOMSLethargyWeight gainConstipationSlowed mentation, forgetfulnessDepressionHair lossDry skinEasy bruisingMenstrual abnormalitiesNeck enlargement/ Goitre

SIGNS-GoiterLow blood pressure and slow pulseHair thinning or lossDry skinConfusionDepressed affectNon pitting edemaHung up reflexes

DIAGNOSISBased on the finding of a low free

thyroxine (T4) level, usually with an elevation in the TSH levels

For patients with hypothyroidism due to pituitary dysfunction (secondary hypothyroidism), both fT4 and TSH are low

There is no role of thyroid scans or iodine uptake testing in patients with hypothyroidism

TREATMENTThyroxine replacementThe usual dose required to achieve full

replacement is between 100-150 ug/dayFor patients with known heart disease or

who are at risk of it, doses are started at 25-50 ug with increases of 25 ug every 4-6 weeks guided by TSH levels

Young patients who are otherwise normal can be started at doses of 100 ug/day

Patients with a TSH<=10.0 do not usually require any therapy

MONITORINGIn general, once a patient

receives a full replacement dose of T4 (usually between 100-150 ug/day) and has a TSH consistently in the normal range, there is little likelihood that their thyroid requirement will change over time

There is no evidence to show the need of re testing to ensure patients are euthyroid in such a sub group of patients

Because T4 and T3 are highly protein bound, any condition where a patient’s serum protein status changes, prompt testing is advocated

This includes conditions that lower serum protein levels such as liver disease, nephrotic syndrome or malnutrition or increase them like pregnancy or estrogen therapy

Patients with subclinical

hypothyroidism (mildly elevated TSH and a normal T4) also benefit from their annual testing of fT4 levels. Approximately 10% of such patients progress to hypothyroidism within 3 yrs of diagnosis. Thereby annual testing is advocated.

COMPLICATIONSMost complications are associated with

under or over treatmentInadequately treated subjects are at a

higher risk of cardiac diseaseOver treatment increases the risk of

atrial fibrillation and osteoporosisHashimoto’s thyroiditis is associated

with other auto immune diseases like Addison’s disease, pernicious anemia, vitiligo. They are also at a higher risk for the future development of lymphoma

De Quervain’s ThyroiditisAlso known as sub acute/ viral/ granulomatous

giant cell thyroiditisMost likely viral in originPresents with neck pain, which may radiate to

the neck or mandibleHoarseness, dysphagia and signs of

thyrotoxicosis may be presentThyroid gland is tender and firmHistopathologically a well developed follicular

lesion that comprises a central core of colloid and surrounded multi nucleate giant cells is characteristic

ESR is high and RAIU is lowNearly always self limiting

Post Partum ThyroiditisIt is the occurrence of thyrotoxicosis,

hypothyroidism or thyrotoxicosis followed by hypothyroidism in the 1st post partum year, in women without overt thyroid disease before pregnancy

Occurs in 8-10% women post partumUpto 30% are anti TPO antibody positivePainless and self limitingLikely to recur in subsequent pregnanciesIncreased risk of developing permanent

primary hypothyroidism in future

Reidel’s ThyroiditisCharacterized by the fibrosis of the

thyroid and adjacent structures Occurs in middle aged womenStony hard, immobile goitre resulting in

pressure symptoms due to the compression of the trachea, oesophagus and the recurrent laryngeal nerve

One third patients have hypothyroidismSurgical removal is indicated when

pressure symptoms are presentGlucocorticoids have beens used for

treatment because of the their anti inflammatory effect

Myxoedema ComaUltimate stage of severe long standing

untreated hypothyroidismOften precipitated by stroke, infection,

myocardial infraction, sedative drugs or exposure to cold

Treatment is started on the basis of clinical suspicion. Initially the precipitating condition needs to be identified and treated, and general suppostive measures instituted

Clinical features include altered sensorium (coma), subnormal temperature, bradycardia, hypotension and features of severe myxoedema

Mortality of this condition is related to

the severity of hypothermiaThroxine 500 ug is given iv stat followed

by 100 ug iv daily (given through nasogastric tube if intravenous formulation is not available)

Glucocorticoid replacement with iv hydrocortisone (5-10 mg/hour) should also be given

External heating should not be done as it causes cutaneous vasodilatation, which increases the strain on the heart

Despite aggressive management, mortality approaches 50%

Euthyroid Sick Syndrome: in severely ill patients during acute physiological stress, the patients may have mildly elevated TSH levels and do not require thyroid replacement. The levels settle within a few weeks of recovery and may sometimes be difficult to distinguish from pre existing or new onset hypothyroidism.

REVISION

MCQs

Q1: the best marker to diagnose thyroid related disorder is:A. T3B. T4C. TSHD. Thyroglobulin

Q2: the lab investigation of a patient shows decreased T3, T4 and TSH. It cannot be?

A. Primary hypothyroidismB. PanhypopituitarismC. Liver DiseaseD. None

Q3: the most common cause of thyroiditis is?

A. Reidel’s thyroiditisB. Hashimoto’s thyroiditisC. Subacute thyroiditisD. Viral thyroiditis

Q4: all of the following are true of de Quervain’s thyroiditis except?

A. PainB. Increased ESRC. Increased radio active iodine

uptakeD. Fever

Q5: Hurthle cells are seen in?

A. Agranulomatous thyroiditisB. Hashimoto’s thyroiditisC. Papillary carcinoma thyroidD. Thyroglossal cyst

Q6: Hung up ankle jerk is seen in?

A. HypothyroidismB. HyperthyroidismC. Diabetes MellitusD. Acromegaly

Q7: All of the following are painless conditions except?

A. Hashimoto’s thyroiditisB. De Quervain’s thyroiditisC. Reidel’s thyroiditisD. Post partum thyroiditis

Q8: All of the following are features of hypothyroidism except?

A. Sinus bradycardiaB. Diastolic hypertensionC. Systolic hypertensionD. Pericardial effusion

Q9: All of the following are features of primary hypothyroidism except?

A. MenorrhagiaB. GoitreC. increased TSHD. Poor secondary sexual

characters

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