HYPOTHYROIDISM ,CAUSES CLASSIFICATION,CLINICAL PICTURE,INVESTIGATIONS AND TREATMENT

     

                                             HYPOTHYROIDISM

Hypothyroidism is a syndrome resulting from deficiency of thyroid harmone,causing many metabolic activities to slow down.

 Clinical Classification of hypothyroidism

(Depending on age group of manifestation)

I.                   Cretinism

II.                Juvenile hypothyroidism

III.             Adult hypothyroidism

Cretinism

It is hypothyroidism arising in the new born

Importance-affected children go for irreversible mental and growth retardation,

if not treated in time.

Diagnosis of cretinism

In early stages-recognition is difficult.

Pointers to diagnosis

Protuberant abdomen with umbilical hernia

hoarse cry,sluggish movements,

delayed mile stones mental and growth retardation

low body temperature, obstinate constipation

Treatment

Start replacement therapy within 2 wks of birth

Juvenile hypothyroidism

Hypothroidism manifesting itself around 5-12 yrs

Pathogenesis-

this is thought to be due to presence of ctopic thyroid whose scant production of thyroid harmone is sufficient to meet the needs of infancy and childhood.

But it is insufficient for demands of later childhood.

Diagnosis;

Closely simulates adult myxedema

Distinguishing feature

1.Retarded growth with dwarfism

2.characteristic body proportion

Upper segment exceeds lower segment

(Upper segment is crown to pubic symphysis

Lower segment is pubic symphysis to ground).

Bone age is impaired

Xray shows epiphysial dysgenesis

Stippling instead of single focus

Best seen in head of femur

Confirmation of diagnosis

Elevated TSH ,low T4,T3 Xray evidence of bone retardation.

ADULT HYPOTHYROIDISM AND MYXEDEMA

Hypothyroidism manifesting itself in adults

Usual age incidence is 40yrs;

commoner in females

Terminologies:

Hypothyroidism and myxedema are different nomenclature for the same condition.

In myxedema hydrophilic mucoprotein ground substance isdeposited  in dermis

Classification of hypothyroidism

Classification depending on involvement of pitutory or otherwise.

I.                   Primary

II.                Secondary hypothyroidism

Secondary hypothyroidism -result of pitutory deficiency/hypothalamic problem

Primary  is result  to intrinsic disorder of thyroid gland

Types of primary hypothyroidism

I.                   Spontaneous atrophy

II.                Goitrous

Hashimatosis

Drug induced

Iodine deficiency

Dysharmanogenesis

Iii          Post ablative

iv.         Transient

v.           Sub clinical

Congenital hypothyroidism

·                     Result of thyroid dysgenesis orEctopic thyroid

·                     In born errors of thyroid harmone metabolism

a.       Inability to trap iodine

b.      Inability to organify iodine

c.       Inability to couple iodo thyroxin

Pathology

In Hashimatosis thyroid is shrunken,fibrosed and atrophic

But in goitrogenoues –thyroid is enlarged 

Spontaneous atrophic hypothyroidism

·         It is primary hypothyroidism

·         Organ specific auto immune disorder like Hashimatosis,or graves disease

·         Throid is destroyed,atrophic and fibrosed

·         And associated with lymphoid infiltration

·         At risk of developing other organ specific  autoimmune condtions

·         Associated with diabetes,pernicious anemia,addisons disease.

·         TSH receptor bodies are present which block endogenous TSH

Goitrous Hypothroidism

Associated with goitrous swelling of thyroid gland

Transient type

Found during ist 6 mths after subtotal thyroidectomy

Or radioactive iodine treatment of graves disease

Subclinical hypothyroidism

Asymptomatic patient clinically euthyroid

But on Lab test thyroid harmones are at lower end of normal or TSH  raised

Hashimatos disease

Common cause of goiter

Age-20-60

F>M

Histology: lymphocytic infiltration, fibrosis and follicular cell hyperplasia

Auto immune disorder

Pathophysiology of hypothyroidism

The effects of hypothyroidism are due to 2 things

1.Due to lower metabolic rate

2.Due to increased amount of muco poly saccharide(hyaluronic acid and chondroitin sulphate)

  - ground substance which is deposited in dermis, tongue and vocal cords.

Effect on systems

SKIN

1. Skin –coarse, thickened, dry,cold, pale, and in extreme cases icthyotic

2. Dryness is due to absence of sweating and sebum secretion

3. Wounds on skin heal slowly.

4. Hair on scalp becomes dry, brittle and falls off.

5. Hair loss on outer 2/3 of eye brow

6. Infiltration causes boggy swelling around the eyes

7.  And swelling on dorsum of the hand  ,feet and supraclavicular fossae

8. Skin also gets a yellowish tinge  due to carotene accumulation-reduced metabolism of carotene with reduced rate of conversion of carotene to vitamin

 Symptom of Cold intolerance

CNS

On account of reduces BMR mental retardation (Slow cerebration)

Lethargic symptom

There is also slowed speech

Muscle contraction and relaxation are slowed

Pseudo myotonic reflex occurs(relaxation phase of DTR prolonged)

Carpel tunnel syndrome.

Heart

Bradycardia.

Myocardial contractility is reduced

Heart sounds are muffled

Cardiomegaly-dilatation or pericardial effusion

Gastro intestinal system

constipation

Lipids

High serum levels of triglycerides and cholesterol

The rate of degradation of lipids  is slower than synthesis

So –atherosclerosis accelerated.

Hematology

Anemia

Reproductive system

Menorrhagia –secondary to anovulatory cycles

.In some women with primary hypothyroidism, amenorrhea develops.

Symptoms

tiredness,lethargy,sleepiness,cold intolerance,hoarseness of voice, low pitched deepened  voice,slurred speech,constipation ,loss of apetite

Severity of hypothyroidism

Spectrum of severity occurs

Ranges from severe hypothyroidism with myxedema

to mere suclinical hypothyroidism

Severe cases may progress to Myxedema coma,

precipitating factors-intercurrent infection,cold exposure,trauma norctics

Head to foot examination in moderate to severe myxedema.

Dull expressionless face with-

Periorbital puffiness

Sparse hair,alopecia

Dry hair

Loss of hair in lateral 1/3rd of eyebrow

Coarse features

Thick lip

Large tongue

Pale  cool rough  skin

Non pitting edema of skin of hands,feet and eye lids.

Deep hoarse voice

deafness

Complication

Myxedema (severe hypothyroidism)

Progress to hypothermic stuperous state called Myxedema coma

Investigations

Serum T3 concentration decreased

Serum T4 concentration decreased

Serum  TSH level raised

Serum TSH level low in pitutory or hypothalamic variety

(Normal level of Thyroid hormones 

Note:From lab to lab reference  range vary

T4- 4-12 µ.gms/100 ml

T3- 80 -200 nano gm/100ml

TSH- 0.5 -5µU/litre)

Treatment

Levo thyroxin sodium 100 µgm per day

Initial daily dose25 µgm /day

At 2-3 wks interval increase by 25-50 µgm.-

Until TSH is within normal range

Usual range is 100-150 µgm /day

 In Secondary hypothyroidism:

First treat adrenal insuffiency ,only then thyroxine must be started

Myxedema coma-Emergency treatment

Rapidly give levothyroxin intravenously over 5 min-

 Add dexamethazone2mg IVorPO every 6 hrs

Then give levothyroxine 100 µgm/day PO or IV  until patient is stabilized.

Simultaneously treat hypovolemia and electrolyte abnormalities

Mechanical ventilation as needed.

Treat hypothermia;/infections

Avoid sedative,narcotics, anesthesia

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