Hypothyroidism

CLASSIFICATION
ETIOLOGICAL
PRIMARY
TRANSIENTSECONDARY

Causes
PRIMARY
1) Congenital
 Agenesis
 Ectopic thyroid remnants
2) Defects of hormone synthesis
 Iodine deficiency
 Dyshormonogenesis
 Drugs -Antithyroid drugs, lithium,
amiodarone, interferon)
3)Autoimmune
 Atrophic thyroiditis
 Hashimoto's thyroiditis
 Postpartum thyroiditis
4) Infective
 Post-subacute thyroiditis
5) Post-surgery
6) Post-irradiation
 Radioactive iodine therapy
 External neck irradiation
7) Infiltration
 Tumour
SECONDARY
1) Hypopituitarism
2) Isolated TSH deficiency
3) Peripheral resistance to thyroid hormone
 Hypothyroidism may be due to primary disease of the thyroid gland(primary) or due to lack of
pituitary TSH(secondary)

investigations
 Classical findings of primary hypothyroidism are reduced levels of
T3 and T4 and increased levels of TSH.
 Secondary hypothyroidism T3, T4, TSH all are reduced, along with
other pituitary hormones.
 Other abnormal investigations are
 Anemia –macrocytic or microcytic (mennoraghia).
 ECG-- bradycardia, low voltage complexes.
 Increase in CK from muscle.
 Hypercholesterolemia.
 Antibodies to thyroid peroxidase are positive in spontaneous
atrophic thyroiditis and hashimoto’s thyroiditis.

treatment
• DRUG OF CHOICE: thyroxine
• Drug should be taken 30 minutes before a meal
• Dose depends on:
a) severity of deficiency
b) Age of patient
c) Fitness of patient

• INITIATION OF THERAPY:
 Based on age
 Young and middle aged adults:100
mcg daily
 Healthy elderly: 50 mcg daily
 With cardiac disease: 25-50 mcg daily

 Based on severity of disease
 Clinical hypothyroidism
i. No residual thyroid function: 100-150
mcg/d
ii. Underlying autonomous function of gland
is present: 75-125mcg/d
 Subclinical hypothyroidism:

• This term is used when TSH is elevated
(>10microUnits per litre) and T3, T4 are normal
with vague symptoms.
• This condition should be treated only if there are
• High titers of antibodies
• Lipid abnormalities
• Associated with goiter
• If above indications are not present then patient
should be followed up with TSH andT3, T4 every
3-6 months.
 DOSE: 25-50 microgram/d
Subclinical hypothyroidism

• DOSE ADUSTMENT AND FOLLOW-UP
 Primary hypothyroidism:
 GOAL-maintain plasma TSH within normal
range
 Plasma TSH is measured 6-8 weeks after
initiation of therapy
 Dose is adjusted in 12-25 mcg increments at 6-
8 week intervals till plasma TSH is normal
 Annual TSH measurement is adequate
thereafter
 Overcorrection of TSH levels will increase the
risk of atrial fibrillation and osteoporosis

 Secondary hypothyroidism
 GOAL: maintain plasma free T4 levels near the
upper limit of the reference range
 Dose is adjusted in 12-25 mcg increments a 6-8
week intervals till plasma TSH is normal
 Annual TSH measurement is adequate
thereafter
 Subclinical hypothyroidism
 Goal:normalise TSH
 Annual evaluation if not treated

MYXOEDEMA COMA
 Myxedema coma is a medical emergency.
 Commonly seen in elderly patients with longstanding
hypothyroidism.
 Common precipitating factors are sedatives , anaesthetics,
pneumonia,CCF, MI, GI bleed, CVA
 Mortality rates are 50%

 Clinical manifestations:
 Hypothermia
 Altered consciousness- result of delayed cerebration .
 Hypoventilation -
 Bradycardia
 Hypoglycemia and SIADH.

Management
 Levothyroxine (T4)
loading dose.:500mcg I.V. bolus
continued at a dose of 50 to 100 mcg/d.
.
 alternative :
liothyronine (T3) :10 to 25 mcg every 8 to
12h .
 Inj. Hydrocortisone 50mg I.V 6hrly should be
given and can be stopped if cortisol levels are
normal.

 Other measures include:
---Oxygen and gradual rewarming.
---Glucose and sodium correction.
---Ventilatory support if required.
• Medication blood levels should be monitored, when
avavilable, to guide dosage.

THYROIDITIS
 Thyroiditis most often results from an infective or
autoimmune process
Classification of thyroiditis
 Acute thyroiditis - Bacterial, viral,
 Subacute thyroiditis - de Quervain's thyroiditis
 Chronic thyroiditis - Autoimmune - Hashimoto’s
(chronic lymphocytic), Riedel thyroiditis

HASHIMOTO’S THYROIDITIS
 It is autoimmune thyroiditis.
 Common in middle aged females.
 Histologically, there is marked lymphocytic
infiltration to the extent of formation of
germinal centers. Askanazy cells are present.
 Gland is diffusely enlarged and is firm.
 Patient may be euthyroid or hypothyroid.
 AntiTPO Ab is positive and thyroid scan
uptake is low.
 Treatment is required only if there is
hypothyroidism or goiter.

Non thyroidal illnesses
T4 to T3 and binding to TBG
TFT: low T3
Normal T4
Normal TSH
THE SICK EUTHYROID SYNDROME

Hypothyroidism

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