2. Hypothyroidism
■ Hypothyroidism is a clinical syndrome resulting from a
deficiency of thyroid hormones.
■ There is a generalized slowing down of metabolic
processes.
■ In newborn infants – Cretinism
■ In adolescents – short stature, mental retardation,
precocious puberty
■ In adults – symptoms largely reversible after therapy
3.
4. Interpretation for Thyroid Function Test
High T4 Normal T4 Low T4
High
TSH
In vivo or in vitro artefact
Pituitary hyperthyroidism
Thyroid hormone resistance
Subclinical hypothyroidism Primary hypothyroidism
Normal
TSH
As above
Sampling within 6 h of
thyroxine dose
Normal
Pituitary or hypothalamic
hypothyroidism
Severe non-thyroidal illness
Low TSH Hyperthyroidism
Subclinical hyperthyroidism
Subtle thyroxine
overreplacement
Autonomous functioning
thyroid nodule
Non-thyroidal illness
Pituitary or hypothalamic
hypothyroidism
Severe non-thyroidal illness
5. Etiology of Hypothyroidism
■ Primary – thyroid failure
■ Secondary – pituitary TSH deficit (Hypopituitarism due to
pituitary adenoma, apoplexy, infiltrative disease-sarcoidosis)
■ Tertiary – hypothalamic deficiency of TRH (rare)
■ Peripheral resistance to the action of thyroid
hormone
6.
7. Hashimoto’s Thyroiditis
■ Chronic lymphocytic thyroiditis
■ Probably the most common cause of hypothyroidism
■ With (younger patients) or without goiter (older patients – atrophy
gland after destruction by immunologic process)
■ High titer of autoantibodies to thyroidal antigens
(Thyroglobulin Ab, Thyroperoxidase Ab = TPO Ab =
Antimicrosomal Ab = AMA)
8. Pathogenesis of Hypothyroidism
■ Characteristic finding: accumulation of
glycosaminoglycans – mostly hyaluronic acid – in
interstitial tissues
■ The accumalation is due not to excessive synthesis but
to decreased destruction of glycosaminoglycans.
■ Accumulation of this hydrophilic substance and
increased capillary permeability to albumin account for
this interstitial edema that is particularly evident in the
skin, heart muscle, and striated muscle.
9. Clinical Manifestations of
Hypothyroidism
■ Symptoms and signs vary in relation to the magnitude of
the thyroid hormone deficiency, and the acuteness with
which the deficiency develops.
❖ Less prominent clinically and better tolerated when
gradual loss of thyroid function (as in most cases of
primary hypothyroidism)
❖ Symptoms develop acutely after thyroidectomy or
abrupt withdrawal of exogenous thyroid hormone
10.
11. Clinical Manifestations of Hypothyroidism -- Skin
■ Cool and pale skin blood flow
■ Dry roughness of skin the epidermis has an
atrophied cellular layer and hyperkeratosis
■ Decreased sweating calorigenesis and acinar gland
secretion
■ Generalized nonpitting edema (myxedema) in severe
hypothyroidism infiltration of the skin with
glycosaminoglycans and associated water retention
12. Clinical Manifestations of Hypothyroidism -- Eyes
■ Periorbital edema -- as a manifestation of generalized
nonpitting edema or Graves' ophthalmopathy.
■ Graves' ophthalmopathy may persist or worsen when
hypothyroidism develops after treatment of Graves'
hyperthyroidism. Patients will have variable degrees of
stare, protrusion of the eyes, and extraocular muscle
weakness.
13. Clinical Manifestations of Hypothyroidism --
Cardiovascular System
■ Bradycardia reductions in heart rate
■ Impaired muscular contractility
■ Reduced cardiac output decreased exercise capacity and
shortness of breath during exercise
■ ECG: low voltage of QRS complexes and P and T waves
■ CXR: cardiomegaly interstitial edema, myofibrillary
swelling, LV dilatation, pericardial effusion
14. Clinical Manifestations of Hypothyroidism --
Cardiovascular System
■ Myxedema induces coronary artery disease ??
■ CAD more common in p’ts with hypothyroidism
■ Symptoms and signs of congestive heart failure are
usually absent in patients who have no other cardiac
disease
■ Congestive heart failure or angina may worsen when
hypothyroidism develops in patients with heart disease
15. Clinical Manifestations of Hypothyroidism --
Cardiovascular System
■ Hypertension peripheral vascular resistance
❖ In normotensive patients, BP increases are small
(<150/100 mmHg).
❖ The BP of patients with established hypertension may
increase further with the development of
hypothyroidism.
16. Clinical Manifestations of Hypothyroidism -- Respiratory
System
■ Fatigue, shortness of breath on exertion, and decreased
exercise capacity impaired respiratory function +
cardiovascular disease
■ Hypoventilation (shallow and slow respirations)
respiratory muscle weakness + reduced pulmonary
responses to hypoxia and hypercapnia
■ Obstructive sleep apnea macroglossia
17. Clinical Manifestations of Hypothyroidism --
Gastrointestinal Disorders
■ Constipation, even ileus gut motility
■ Decreased taste sensation
■ Gastric atrophy presence of antiparietal cell antibodies.
Pernicious anemia occurs in 10% of patients with
hypothyroidism caused by chronic autoimmune thyroiditis.
■ Weight gain decreased metabolic rate + accumulation of
fluid (nonpitting edema) that is rich in glycosaminoglycans
■ Ascites, rare
18. Clinical Manifestations of Hypothyroidism -- Renal
Function
■ Decreased glomerular filtration rate (GFR )
■ Impaired ability to excrete a water load
■ The drug clearance (ex, antiepileptic, anticoagulant,
hypnotic and opioid drugs), is decreased. Drug toxicity
may occur if drug dosage is not reduced.
■ During T4 replacement, drugs that are administered at
effective doses in patients who are hypothyroid may
become less effective.
19. Clinical Manifestations of Hypothyroidism -- Anemia
■ Impaired hemoglobin synthesis thyroxine deficiency
■ Iron deficiency increased iron loss with menorrhagia
+ impaired intestinal absorption of iron
■ Folate deficiency impaired intestinal absorption of
folic acid
■ Pernicious anemia vitamin B12 -deficient
megaloblastic anemia
20. Clinical Manifestations of Hypothyroidism -- Reproductive
Abnormalities
■ Women with hypothyroidism may have either oligo- or
amenorrhea or hypermenorrhea-menorrhagia.
■ Decreased fertility
■ Increased likelihood for early abortion
■ Hyperprolactinemia may occur, and is occasionally
sufficiently severe to cause amenorrhea or galactorrhea
■ The serum sex hormone-binding globulin concentration
may be low in hypothyroidism. This will lower serum total
but not free sex hormone concentrations.
21. Clinical Manifestations of Hypothyroidism -- Neurological
Dysfunction
■ General depression of central nervous system function
■ Sleepiness, inability to concentrate
■ Sluggish thought processes
❖ Respond slowly to questions
❖ Less able to retrieve information from memory
■ Agitated psychosis, rare (“myxedema madness”)
■ PET: 23% reduction in cerebral blood flow and a 12%
reduction in cerebral glucose metabolism
22. Clinical Manifestations of Hypothyroidism --
Neuromuscular Abnormalities
■ A delay in the relaxation phase of deep tendon reflexes
■ Carpal tunnel syndrome
■ Paresthesia
■ Asymptomatic elevation in serum CPK level to muscle
hypertrophy (which may be accompanied by muscle
cramps) to proximal muscle weakness to, in rare cases,
rhabdomyolysis.
23. Clinical Manifestations of Hypothyroidism -- Metabolic
Abnormalities
■ Hyponatremia may result from a reduction in free water
clearance
■ Reversible increases in serum creatinine occur in 20 ~ 90%
of hypothyroid patients
■ lipid clearance may be decreased, resulting in an elevation
in the serum concentrations of free fatty acids and total and
low-density lipoprotein cholesterol
■ Plasma homocysteine concentrations are increased in
some hypothyroid patients,
25. Serum FT4, TSH
Normal FT4, TSH
TSH , FT4
FT4 , TSH normal or
Primary
hypothyroidism
Euthyroid
Secondary hypothyroidism
TRH test
Excessive
response
Normal type
response No response
Pituitary
lesion
Hypothalamic
lesion
Primary
hypothyroidism
26. Treatment of Hypothyroidism
■ Replacement of Triiodothyroxine (T3): unsatisfactory due
to rapid absorption, short half-life, and transient effect
■ Levothyroxine (T4):
❖ Converted to T3 intracellularly
❖ Once daily, half-life: 7 days
❖ Well-absorbed
❖ Easily monitored by following serum TSH and T4
levels
27. Treatment of Hypothyroidism
■ Replacement does of levothyroxine in adults range from
0.05 to 0.2 mg/d. It varies according to the patient’s age
and body weight.
■ In young children: 4-5 ug/kg/d
■ In adults: average 1.7 ug/kg/d
■ In elders, start with lower dose, ex. 0.025mg daily, increase
the dose at 4- to 6-week intervals based on serum FT4 and
TSH levels
■ Dose should be increased about 25% during pregnancy
28. Drugs Potentially Altering Thyroid Hormone Replacement Requirements
Increase replacement requirements
Drugs that reduce thyroid hormone production
Lithium
Iodine-containing medications
Amiodarone (Cordarone)
Drugs that reduce thyroid hormone absorption
Sucralfate (Carafate)
Ferrous sulfate (Slow Fe)
Cholestyramine (Questran)
Colestipol (Colestid)
Aluminum-containing antacids
Calcium products
Drugs that increase metabolism of thyroxine
Rifampin (Rifadin)
Phenobarbital
Carbamazepine (Tegretol)
Warfarin (Coumadin)
Oral hypoglycemic agents
Increase thyroxine availability and may decrease replacement requirements
Drugs that displace thyroid hormone from protein binding
Furosemide (Lasix)
Mefenamic acid (Ponstel)
Salicylates
