Hypothyroidism

hypothyroidism-causes,clinical features,investigation,treatment

1. HYPOTHYROIDISM 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. P athogenesis 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 f ree T4 and T3 Anti-TPO and anti- Tg antibodies Thyroid Ultrasound :- for the diagnosis and evaluation of patients with nodular thyroid disease.

14. 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 .

15. 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.

16. 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.

17. SUBCLINICAL HYPOTHYROIDISM S ubclinical 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.

18. 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.

19. 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).

20. 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.

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