Case Presentation A 50-years-old woman presented to the ED with
chest pain and dyspnea. On the day of admission she collapsed and
was unresponsive for a short while. She had not suffered from any
episodes of syncope before. PMH: single kidney; no h/o DM or HTN
Physical examination revealed a well nourished woman with a blood
pressure of 90/60 mmHg and a pulse rate of 100 beats per minutes.
She had a puffy face and examination of the neck revealed no struma
(a swelling in the neck due to an enlarged thyroid gland). The
jugular venous pressure was normal. Cardiac auscultation was normal
and the lungs were clear. Peripheral pulses of radial, femoral and
dorsalis pedis were present. ECG was done and is shown.
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She received magnesium and was transferred to the CCU.
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Next ECG obtained from the patient revealed T wave inversion
and prolongation of QT intervals of 0.71 S. The patient received
phenytoin as treatment for prolongation of QT intervals. At the
third day of admission the patient developed positional vertigo and
her blood pressure dropped to 80mmHg. Diagnostic laboratories were
drawn.
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Thyroid function test revealed Total T 4 0.71 g/dL, free T 4
(FT4) 0.1 ng/mL, total T 3 74 g/dL and thyroid stimulating hormone
36 U/mL. Other laboratory data such as blood urea nitrogen (BUN),
Creatinine and electrolytes were in normal range. The patient
received levothyroxine 100 g/day. Two months after treatment with
levothyroxine, QT intervals normalized and ventricular tachycardia
was abolished. Her periorbital edema had diminished and both TSH
and free T4 had normalized.
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HYPOTHYROIDISM
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Objectives Identify Risk Factors for hypothyroidism Discuss
clinical presentation, signs and symptoms of hypothyroidism
Diagnose and distinguish primary, secondary and tertiary
hypothyroidism Discuss treatment of hypothyroidism
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Risk Factors Personal history Previous thyroid dysfunction
Goiter Surgery or radiotherapy affecting the thyroid gland DM
Vitiligo Pernicious anemia Leukotrichia (premature gray hair)
Medications and other compounds Family history Thyroid disease
Pernicious anemia DM Primary adrenal insufficiency
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Clinical Presentation Symptoms and signs of the disease vary in
relation to the magnitude of the thyroid hormone deficiency and
acuteness with which the deficiency develops May be modified by
factors such as coexisting nonthyroidal illness Hypothyroidism
caused by hypothalamic-pituitary disease may have associated
endocrine deficiencies masking the manifestations of hypothyroidism
Hypothyroidism after treatment of Graves' hyperthyroidism, some
manifestations may persist throughout the patient's life 5-8x more
likely in women
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Many of the manifestations of hypothyroidism reflect one of two
changes induced by lack of thyroid hormone 1.A generalized slowing
of metabolic processes. This can lead to abnormalities such as
fatigue, slow movement and slow speech, cold intolerance,
constipation, weight gain, delayed relaxation of deep tendon
reflexes, and bradycardia. 2.Accumulation of matrix
glycosaminoglycans in the interstitial spaces of many tissues This
can lead to coarse hair and skin, puffy facies, enlargement of the
tongue, and hoarseness. These changes are often more easily
recognized in young patients, and they may be attributed to aging
in older patients.
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Common Signs and Symptoms of Thyroid Dysfunction Hypothyroidism
Fatigue Weight gain Cold intolerance Skin dryness Hair dryness or
loss Depression Dementia Muscle cramps and myalgias Edema
Bradycardia Constipation Menstrual irregularity (especially
menorrhagia) Infertility Hyperthyroidism Fatigue Weight loss Heat
intolerance Hyperhydrosis Nervousness Insomnia Tremor Muscle
weakness Dyspnea Palpitations Tachycardia and atrial
tachyarrhythmias Hyperdefecation Menstrual irregularity (especially
hypomenorrhea)
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Pretibial Myxedema
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DIAGNOSIS Primary vs. Secondary or Tertiary Hypothyroidism
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Major causes of hypothyroidism Primary hypothyroidism: Chronic
autoimmune thyroiditis Iatrogenic Thyroidectomy, radioiodine
therapy or radiation Iodine deficiency or excess Drugs Thionamides,
lithium, amiodarone, INF Infiltrative diseases Transient
hypothyroidism Painless thyroiditis, postpartum, Congenital thyroid
agenesis, dysgenesis, or defects in hormone synthesis Central
hypothyroidism TSH deficiency TRH deficiency Pituitary mass lesions
Radiation Surgery Infiltrative disorders Sarcoid, TB,
hemochromatosis, syphilis, fungal infections Generalized thyroid
hormone resistance
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UpToDate
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Primary Hypothyroidism 95% of cases of hypothyroidism Caused by
disease of the thyroid gland with decreased secretion of thyroxine
(T4) and triiodothyronine (T3) -> reduction in the serum
concentrations of the two hormones -> compensatory increase in
TSH secretion Characterized by a high serum TSH concentration and a
low serum free T4 concentration
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Forms of primary hypothyroidism Subclinical hypothyroidism high
serum TSH concentration in the presence of normal serum free T4 and
T3 concentrations few if any symptoms and signs of hypothyroidism
Overt hypothyroidism high serum TSH concentration in the presence
of a low serum free T4 concentration symptoms and signs of
hypothyroidism
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Hashimotos thyroiditis Chronic autoimmune (Hashimoto's)
thyroiditis Cell- and antibody-mediated destruction of thyroid
tissue: 1.Cytotoxic T cells may directly destroy thyroid cells.
2.More than 90 percent of patients have high serum concentrations
of autoantibodies to thyroglobulin, thyroid peroxidase, or the
thyroid Na/I transporter
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Nuclear accidents and thyroid French prophylaxis: In an
individual with a healthy thyroid, taking 100 mg of stable iodine
immediately before exposure to radioactive iodine reduces the dose
to the thyroid by at least 95% Distribute iodine around nuclear
sites Chernobyl Accident: The 26 April 1986 accident at the
Chernobyl nuclear power plant contaminated large areas of northern
Ukraine as well as parts of Belarus and the Russian Federation. The
environmental fallout included radionuclides of iodine, primarily
iodine-131 ( 131 I), which concentrates in the thyroid gland
increased prevalence of thyroid cancer and subclinical
hypothyroidism significant relationship between prevalence of
hypothyroidism and individual 131 I thyroid doses due to
environmental exposure
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Central Hypothyroidism (Secondary and Tertiary) Insufficient
stimulation of the thyroid gland by TSH, by either hypothalamic
(tertiary) or pituitary (secondary) disease Low serum T4
concentration and a serum TSH concentration not appropriately
elevated Suspect when: Known hypothalamic or pituitary disease
Pituitary mass lesion is present Symptoms and signs of
hypothyroidism associated with other hormonal deficiencies