hypothyroidism-causes,clinical features,investigation,treatment

1. - Dr Rahul Arya
- Assistant Professor
- Department of Medicine

2. ANATOMY
• Thyroid gland consist of two lobes
connected by an isthmus.
• Location : anterior to trachea
between cricoid cartilage and
suprasternal notch.
• It is 20 gm in size and is highly
vascular and soft in consistency.
• Four parathyroid glands are located
posterior to each thyroid lobe.

3. Synthesis of Thyroid Hormone

4. Regulation of Thyroid Hormone Secretion

5. Thyroid Hormones
• Thyroid gland secretes mostly T4 and some T3.
• Serum concentration T4- 8 µg/dL
T3- 0.14 µg/dL
• Half life T4- 7 days
T3- 2 days
• T3 and T4 are bound to plasma proteins like Thyroid binding globulin (TBG),
albumin and transthyretin (TTR, formerly known as thyroxine binding pre-
albumin).

6. • 99.98% of T4 and 99.7% of T3 are protein bound.
• T3 is more metabolically active than T4.
• In the periphery T4 is converted into T3 by deiodinase enzyme.

7. Causes of Hypothyroidism

8. • Iodine deficiency remains a common cause of hypothyroidism
worldwide.
• In areas of iodine sufficiency, autoimmune disease (Hashimoto’s
thyroiditis) and iatrogenic causes (treatment of hyperthyroidism) are
most common.

9. AUTOIMMUNE HYPOTHYROIDISM
• It may be associated with a goiter (Hashimoto’s, or goitrous
thyroiditis) or, at the later stages of the disease, minimal residual
thyroid tissue (atrophic thyroiditis).
• Initially subclinical then become overt or clinical hypothyroidism.
• Prevalence : 4 per 1000 women and 1 per 1000 men
• The mean age at diagnosis is 60 years, and the prevalence of overt
hypothyroidism increases with age.

10. Pathogenesis
• Thyroid antigen as foreign  chronic immune reaction 
lymphocytic infiltration of gland  progressive destruction of
functional thyroid tissue.
• Anti-thyroid peroxidase antibodies are hallmark of this disease.

11. Clinical Manifestations- Symptoms
• Tiredness, weakness
• Dry skin
• Feeling cold
• Hair loss
• Difficulty concentrating and poor memory
• Constipation
• Weight gain with poor appetite
• Dyspnea
• Hoarse voice
• Menorrhagia (later oligomenorrhea or amenorrhea)
• Paresthesia
• Impaired hearing

12. Clinical Manifestations- Signs
• Dry coarse skin; cool peripheral extremities
• Puffy face, hands, and feet (myxedema)
• Diffuse alopecia
• Bradycardia
• Peripheral edema
• Delayed tendon reflex relaxation
• Carpal tunnel syndrome
• Serous cavity effusions

13. LABORATORY EVALUATION
• Measurement of Thyroid Hormones
- TSH
- free T4 and T3
• Anti-TPO and anti-Tg antibodies
• Thyroid Ultrasound :- for the diagnosis and evaluation of patients
with nodular thyroid disease.

15. Treatment
• If there is no residual thyroid function, the daily replacement dose of
levothyroxine is usually 1.6 μg/kg body weight ideally taken at least 30 min
before breakfast.
• Adult patients under 60 years old without evidence of heart disease may
be started on 50–100 μg levothyroxine daily.
• The dose is adjusted on the basis of TSH levels, with the goal of treatment
being a normal TSH, ideally in the lower half of the reference range.
• TSH responses are gradual and should be measured about 2 months after
instituting treatment or after any subsequent change in levothyroxine
dosage.

16. • Adjustment of levothyroxine dosage is made in 12.5- or 25-μg
increments if the TSH is high.
• Decrements of the same magnitude should be made if the TSH is
suppressed.
• In the elderly, especially patients with known coronary artery disease,
the starting dose of levothyroxine is 12.5–25 μg/d with similar
increments every 2–3 months until TSH is normalized.

17. • The clinical effects of levothyroxine replacement are slow to appear.
• Patients may not experience full relief from symptoms until 3–6
months after normal TSH levels are restored.
• Once full replacement is achieved and TSH levels are stable, follow-up
measurement of TSH is recommended at annual intervals and may be
extended to every 2–3 years if a normal TSH is maintained over
several years.

18. SUBCLINICAL HYPOTHYROIDISM
• Subclinical hypothyroidism refers to biochemical evidence of thyroid
hormone deficiency in patients who have few or no apparent clinical
features of hypothyroidism.
• levothyroxine is recommended if the patient is a woman who wishes to
conceive or is pregnant, or when TSH levels are above 10 mIU/L.
• When TSH levels are below 10 mIU/L, treatment should be considered
when patients have suggestive symptoms of hypothyroidism, positive TPO
antibodies, or any evidence of heart disease.

19. • Treatment is administered by starting with a low dose of
levothyroxine (25–50 μg/d) with the goal of normalizing TSH.
• If levothyroxine is not given, thyroid function should be evaluated
annually.
• It is important to confirm that any elevation of TSH is sustained over a
3-month period before treatment is given.

20. Hypothyroidism in pregnancy
• Women with a history or high risk of hypothyroidism should ensure
that they are euthyroid prior to conception and during early
pregnancy because maternal hypothyroidism may adversely affect
fetal neural development and cause preterm delivery.
• Thyroid function should be evaluated immediately after pregnancy is
confirmed and every 4 weeks during the first half of the pregnancy,
with less frequent testing after 20 weeks’ gestation (every 6–8 weeks
depending on whether levothyroxine dose adjustment is ongoing).

21. • The levothyroxine dose may need to be increased by up to 50%
during pregnancy, with a goal TSH of less than 2.5 mIU/L during the
first trimester and less than 3.0 mIU/L during the second and third
trimesters.
• After delivery, thyroxine doses typically return to prepregnancy
levels.