2. DEFINITION
It is a syndrome characterised by the
clinical and biochemical
manifestations of thyroid hormone
deficiency in the target tissues of
thyroid hormone.
Hypothyroidsm is a graded
phenomenon ranges from subclinical
hypothyroidsm to myxedema coma.
3. HISTORY
GULL (1874) – Defined hypothyroidsm as clinical
syndrome (myxedema)
Murray (1891) – cured myxedema by hypodermic
inj of sheep thyroid extract
Kendall (1914) – isolated thyroxine
Harrington (1926) – identified constitution of
thyroxine and synthesize it
1960s – levothyroxine sodium used for treatment
4. HYPOTHYROIDISM
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
8. CONGENITAL
HYPOTHYROIDISM
transient, especially if the mother has TSH-R blocking antibodies or
has received antithyroid drugs
Neonatal hypothyroidism is due to
◦ thyroid gland dysgenesis in 80–85%,
◦ inborn errors of thyroid hormone synthesis in 10–15%(dyshormonogenetic
goiter)
◦ TSH-R antibody-mediated in 5% of affected newborns.
The developmental abnormalities are twice as common in girls.
Transplacental passage of maternal thyroid hormone occurs
before the fetal thyroid gland begins to function and provides
partial hormone support to a fetus with congenital
hypothyroidism
10. CONGENITAL HYPOTHYROIDISM
Clinical Manifestations
appear normal at birth,
prolonged jaundice, feeding problems,
hypotonia, enlarged tongue,
delayed bone maturation, and umbilical hernia.
permanent neurologic damage results if treatment
is delayed.
Typicalfeatures of adult hypothyroidism may also
be present
Other congenital malformations, especially cardiac,
are four times more common in congenital
hypothyroidism.
11. CRETINISM
Cretinism: (from the French chrétien, meaning
“Christian” or “Christlike,” mentally retarded as to
be incapable of sinning)
◦ hypothyroidism that develops in infancy or
early childhood
◦ mental and growth retardation
◦ coarse facial features, a protruding tongue, and
umbilical hernia.
◦ often born to mothers with iodine deficiency
◦ Concomitant selenium deficiency may also
contribute to the neurologic manifestations
13. CONGENITAL HYPOTHYROIDISM
Diagnosis and Treatment
Neonatal screening programs measurement of
TSH or T4 levels in heel-prick blood specimens.
T4 requirements are relatively great during the
first year of life (dose of 10–15 μg/kg per day,
and titrated according to tsh)
Early treatment with T4 results in normal IQ
levels
14. AUTOIMMUNE
HYPOTHYROIDISM
-Hashimoto’s,or goitrous thyroiditis
-Atrophic thyroiditis.
Because the autoimmune process gradually reduces
thyroid function, there is a phase of compensation
when normal thyroid hormone levels are maintained by
a rise in TSH-subclinical hypothyroidism.
Later, unbound T4 levels fall and TSH levels rise further;
symptoms become more readily apparent at this stage
(usually tsh >10 mIU/l), which is referred to as clinical
hypothyroidism or overt hypothyroidism.
15. Hashimoto thyroiditis/
struma lymphomatosa
An autoimmune disease that results in destruction
of the thyroid gland and gradual and progressive
thyroid failure
Between 45 and 65 years
Female predominance of 10 : 1 to 20 : 1. Also in
children
Circulating autoantibodies:
Antimicrosomal,
Antithyroid peroxidase, and
Antithyroglobulin antibodies
Abnormalities of regulatory T cells (Tregs), or exposure
of normally sequestered thyroid antigens
The thyroid follicles are atrophic and are lined by
epithelial cells distinguished by the presence of
abundant eosinophilic, granular cytoplasm, termed
hürthle cells in conjunction with a heterogeneous
population of lymphocytes
16.
17. RISK FACTORS FOR AUTOIMMUNE
HYPOTHYROIDISM
◦ A high iodine intake
◦ decreased exposure to microorganisms in childhood
◦ HLA-DR3, -DR4, and -DR5 in Caucasians
◦ CTLA-4, a T cell–regulatory gene
◦ Protein tyrosine phosphatase-22 (PTPN22),
◦ Down’s syndrome(A gene on chromosome 21)
Female preponderance of thyroid autoimmunity due to
◦ sex steroid effects on the immune response,
◦ X chromosome–related genetic factor(Turner’s syndrome)
19. Clinical Manifestations
Hashimoto’s thyroiditis
Insidious onset
Painless enlargement of the thyroid
Goiter -irregular and firm
Complicated hashimoto’s
thyroiditis:associated with pain
Patient may become aware of symptoms
only when euthyroidism is restored
Hypothyroidism develops gradually
preceded by transient thyrotoxicosis caused
by disruption of thyroid follicles, leading to
release of thyroid hormones
20.
21. Clinical Manifestations
atrophic thyroiditis
Dry skin
decreased sweating,
thinning of the epidermis,and
Increased dermal glycosaminoglycan content traps
water, giving rise to skin thickening without pitting
(myxedema).
Typical features include a puffy face with edematous
eyelids and nonpitting pretibial edema
pallor
yellow tinge to the skin due to carotene accumulation.
Nail growth is retarded
hair is dry, brittle, difficult to manage, and falls out easily
diffuse alopecia
thinning of the outer third of the eyebrows
22. NEUROLOGIC PROBLEMS
Carpal tunnel and other entrapment
syndromes
Impairment of muscle function with
stiffness, cramps, and pain.
Slow relaxation of tendon reflexes
Pseudomyotonia.
Memory and concentration are impaired.
Reversible cerebellar ataxia,
Dementia,
Psychosis, and
Myxedema coma
23. CLINICAL PRESENTATION-
SKIN
PUFFY FACE, HANDS, FEET- NON PITTING
ENLARGED TONGUE
COOL PERIPHERY
DRY COARSE SKIN
HAIR- DRY, BRITTLE, FALLS OUT
MADAROSIS- NOT SPECIFIC
BRITTLE NAILS
VITILIGO
MYXEDEMA- ACCUMULATION OF
HYGROSCOPIC GLYCOSAMINOGLYCAN
PRETIBIAL MYXEDEMA- GRAVES’
DISEASE
32. MYXEDEMA
Hypothyroidism developing in the older child or adult.
Reduced cardiac output probably contributes to shortness of
breath and decreased exercise capacity,
Hypothyroidism promotes an atherogenic profile—an
increase in total cholesterol and LDL levels
Accumulation of matrix substances, such as
glycosaminoglycans and hyaluronic acid, in skin,
subcutaneous tissue, and a number of visceral sites.
◦ Nonpitting edema,
◦ Broadening and coarsening of facial features,
◦ Enlargement of the tongue, and
◦ Deepening of the voice.
33.
34. LABORATORY EVALUATION
A normal TSH level excludes primary (but not
secondary) hypothyroidism
Circulating unbound T3 levels are normal in
about 25% of patients, reflecting adaptive
deiodinase responses to hypothyroidism
T3 measurements
TPO antibodies, present in >90% o
Tbii found in 10–20%
FNA biopsy
Increased creatine phosphokinase,
Elevated cholesterol and triglycerides,
Anemia (usually normocytic or macrocytic).
35. SUBCLINICAL
HYPOTHYROIDISM
Refers to biochemical evidence of thyroid hormone
deficiency in patients who have few or no apparent
clinical features of hypothyroidism.
4–10% of the general population but increases to
20% in women older than age 50
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.
36. Thyroid Preparations
Synthetic(levothyroxine, liothyronine, liotrix) or of
animal origin (desiccated thyroid).
Liotrix :more expensive;mixture of thyroxine and
liothyronine
Synthetic levothyroxine is the preparation of choice
◦ Stability
◦ Content uniformity,
◦ Low cost,
◦ Lack of allergenic foreign protein,
◦ Easy laboratory measurement of serum levels,
and
◦ Long half-life (7 days), which permits once-daily
administration
37. Although liothyronine is three to four times more
potent than levothyroxine, it is not recommended
for routine replacement because of
◦ shorter half-life (24 hours), which requires
multiple daily doses;
◦ Its higher cost; and
◦ The greater difficulty of monitoring its adequacy
of replacement by conventional laboratory tests.
◦ Greater risk of cardiotoxicity, avoided in patients
with cardiac disease.
◦ Best used for shortterm suppression of tsh.
38. Desiccated thyroid:disadvantages:
◦ Protein antigenicity,
◦ Product instability,
◦ Variable hormone concentrations, and
◦ Difficulty in laboratory monitoring far outweigh the advantage of
lower cost
Equi-effective doses are 100 mg of desiccated thyroid,100 mcg of
levothyroxine, and 37.5 mcg of liothyronine
The shelf life of synthetic hormone preparations is about 2 years,
Particularly if they are stored in dark bottles to minimize
spontaneous deiodination.
The shelf life of desiccated thyroid is not known with certainty, but its
potency is better preserved if it is kept dry
Infants and children require more T4 per kilogram of body weight
than adults.
Average dosage for an infant 1–6 months of age is 10–15 mcg/kg/d,
whereas the average dosage for an adult is about 1.7 mcg/kg/d.
Older adults (> 65 years of age) may require less thyroxine for
replacement
39. Certain foods (eg, bran, soy, coffee) and drugs can impair its
absorption,
◦ Thyroxine should be administered on an empty stomach
(eg, 30 minutes before meals or 1 hour after meals or at
bedtime).
Tsh maintained within an optimal range of 0.5–2.5 mu/L. It
takes 6–8 weeks after starting a given dose of thyroxine to
reach steady-state levels in the bloodstream
In older patients, the heart is very sensitive to the level of
circulating thyroxine, and if angina pectoris or cardiac
arrhythmia develops, it is essential to stop or reduce the dose
of thyroxine immediately
40. Dosage of 12.5–25 mcg/d for 2 weeks, increasing the
daily dose by 12.5–25 mcg every 2 weeks until
euthyroidism or drug toxicity is observed
Chronic overtreatment with T 4 ,particularly in elderly
patients, can increase the risk of atrial fibrillation and
accelerated osteoporosis
If coronary artery surgery is indicated, it should be
done first, prior to correction of the myxedema by
thyroxine administration.
41. TREATMENT Hypothyroidism
CLINICAL HYPOTHYROIDISM
If there is no residual thyroid function, the daily
replacement dose of levothyroxine is usually 1.6
μg/kg body weight (typically 100–150 μg), ideally
taken at least 30 min before breakfast.
If patients develop hypothyroidism after the
treatment of graves’ disease, there is often
underlying autonomous function, necessitating
lower replacement doses (typically 75–125 μg/d).
42. Adult patients under 60 years old without evidence
of heart disease may be started on 50–100 μg
levothyroxine (T4) daily.
Tsh responses should be measured about 2
months after instituting treatment or after any
subsequent change in levothyroxine dosage.
Patients may not experience full relief from
symptoms until 3–6 months after normal tsh levels
are restored.
43. Adjustment of levothyroxine dosage is made in
12.5- or 25-μg increments if the TSH is high;
Patients with a suppressed TSH of any cause,
including T4 overtreatment, have an increased risk
of atrial fibrillation and reduced bone density.
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.
44. In patients of normal body weight who are
taking ≥200 μg of levothyroxine per day, an
elevated tsh level is often a sign of poor
adherence to treatment.
Because t4 has a long half-life (7 days),
patients who miss a dose can be advised to
take two doses of the skipped tablets at
once.
45. Other causes of increased
levothyroxine requirements
malabsorption(e.g., celiac disease, small-bowel surgery),
estrogen or selective estrogen receptor modulator therapy,
ingestion with a meal,
drugs that interfere with T4 absorption or metabolism such as
◦ cholestyramine,
◦ ferrous sulfate,
◦ calcium supplements,
◦ proton pump inhibitors,
◦ lovastatin,
◦ aluminum hydroxide,
◦ rifampicin,
◦ amiodarone,
◦ carbamazepine,
◦ phenytoin, and
◦ tyrosine kinase inhibitors.