HYPOTHYROIDISM:

HYPOTHYROIDISM
Hypothyroidism

DEFINITION:

Decrease secretion of thyroid hormone is called hypothyroidism.

HORMONES OF THYROID GLAND:


The thyroid gland secrets:

  • Tetra iodothyronin T4 (thyroxin)
  • Tri iodothyroinin T3
HALF LIFE:
T4 has a longer half-life while T3 has a short half-life.

CLASSIFICATION OF HYPOTHYROIDISM:

BASIC CONCEPT:

When the gland is not functioning properly, the gland will produce less amount of T3 & T4, so pituitary gland will secrete more and more TSH. This more and more secretion of TSH will try to maintain normal T3 & T4 level.

SUBCLINICAL HYPOTHYROIDISM:

The initial state of hypothyroid where TSH is increase & T3T4 is normal is known as subclinical hypothyroidism.

PRIMARY HYPOTHYROIDISM:

In the latter stage of the disease, T3/T4 level will also reduce and TSH will remains high, so when the disease occurs at thyroid level (primary hypothyroid).

SECONDARY HYPOTHROIDISM:

If the disease occur at pituitary gland level, this is called secondary hypothyroidism.

TERTIARY HYPOTHROIDISM:

When the disease occur at the level of hypothalamus, this is called tertiary hypothyroidism.

CAUSES:

Hashimotothroiditis: 

  • A Chronis lymphocytic thyroiditis that is consider to be an autoimmune disorder.
  • As a result treatment of hyperthyroidism.
  • Surgical excision of thyroid gland
  • Goiter

Drug induced: 

Lithium, amioderone.

CLINICAL FEATURES:

CARDIOUASCULAR SYSTEM:

Hypothyroidism can lead to decrease in the heart rate and can cause bradycardia.
Thyroid hormones increases the force of contraction of the heart, so in the absence of thyroid hormone, it decrease the force of contraction & cardiac output.

GROWTH AND DEVELOPMENT:

What you are finding that the brain growth occurs in first 3-4 years of life.
For example, a child have hypothyroidism even if we go for replacement therapy, the child may develop normal somatic growth/sexual growth but he will be mentally retorted because the maximum brain growth occurs in the first 3-4 years of the life that’s why hypothyroid patients are

  • Mental retardation
  • Growth retardatio

SEXUAL FUNCTIONS:

MALE: 

hypothyroidism leads to loss of libido/sexual drive what happen to menstruation. (Abnormal menstrual flow)

FEMALE:

 menstruation/menorrhagia (excess of bleeding occur).

BLOOD: 

  • Microcytic anemia (Due to menorrhagia).
  • Macrocytic anemia (autoimmune).
  • Deficiency of vitamin-B12/folic acid.
  • Sideroblastic anemia.

GIT:

  • Pt might come with chronic constipation
  • Pt might come with weight gain.
  • Hypothyroidism is often confused with obesity & depression.
  • Thyroid function test will give accurate diagnosis
  • Abdominal distension
  • Loss of appetite.

CNS:

  • Dementia 
  • Reversible dementia   -    hypothyroid
  • Vitamin-B12 deficiency 
  • Cerebral ataxia      -    subdural hematoma 

OTHER CLINICAL FEATURES:



  • LDH (pronto coronary artery disease
  • LDH
  • DIAGNOSIS:
  • Thyroid function test,
  • Serum total thyroxin TT4 (<5 )
  • Serum tri iodothronine
  • Serum thyrotropin TSH assay 

TREATMENT:

All the pts with symptomatic hypothyroidism require replacement therapy.
Initial dose of T4 depends on pts age, severity and duration of the disease and co-existence of cardiac disease.

ADULTS: 

Start with the lowest possible dose and gradually increase why because if we suddenly give full dose the heart rate will be increase.
In adult they also have increase LDH and have atherosterosis that can precipitated.

CHILDREN: 

we give full dose because,
We have not concern with the heart but with the brain
T4  dose:50-100 g daily
Longer half-life so given once daily in morning
After 6 weeks----thyroid function test
TSH concentration is the best indicator.
As TSH increase----inadequate treatment

DOSE FOR ADULTS: 

25 g and increasing slowly after 4-6 weeks and progress should be daily monitor.
Some recommends T3 because if adverse effect occurs, these can be alleviated by dose reduction due to shorter half-life of T3.
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Haseenullah Shah

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