Hypothyroidism, Subacute Thyroiditis Flashcards
A disease state caused by insufficient circulating thyroid hormone
Hypothyroidism
Thyroid hormone deficiency caused by thyroid gland destruction or dysfunction
Primary hypothyroidism
Ex: Hashimoto’s thyroiditis
Most common cause of hypothyroidism
Hashimoto’s thyroiditis
Thyroid hormone deficiency caused by pituitary insufficiency
TSH deficiency occurs in the context of other anterior pituitary hormone deficiencies
Isolated TSH deficiency is rare
Secondary hypothyroidism
Thyroid hormone deficiency caused by hypothalamic disease or disruption of hypothalamic pituitary portal blood flow
TRH deficiency usually occurs in the context of other hypothalamic hormone deficiencies
Isolated TRH deficiency is very rare
Tertiary hypothyroidism
Elevated serum TSH
Normal free T4
Subclinical hypothyroidism
Autoimmune Hashimoto’s thyroiditis
Epidemiology
Incidence
Mean age
Sex
Risk
Other predisposing factors
W 400: 100,000
M 100: 100,000
60 years
Prevalance increases with age
Rarely seen in children
Common in Japanese
High iodine diet
Most common cause worldwide of hypothyroidism
Iodine deficiency
Most common cause of hypothyroidism in iodine-sufficient regions
Autoimmune Hashimoto’s Thyroiditis
Autoimmune disorder with genetic and environmental susceptibilities
Characterized by marked lymphochytic infiltration
atrophy of the thyroid follicles
absence of colloid
fibrosis
Leading to thyroid gland destruction
Hashimoto’s thyroiditis
Thyroid-cell destruction is believed to be primarily mediated by
CD8+ cytotoxic T cells
CD8 cytotoxic t cells destroy their targets by
Perforin induced cell necrosis
Granzyme B-induced apoptosis
Thyroid cells are rendered susceptible to apoptosis because of cytokines
IL - 1
TNF
IFN
End stage of Hashimoto’s thyroiditis
More extensive fibrosis
Less pronounced lymphocytic infiltration
Absence of thyroid follicles
Atrophic thyroiditis
Primary Hypothyroidism etiology
Surgical: thyroidectomy Radiation for iodine treatment in hyperthyroidism External radiation of neck for lymphoma Drugs Congenital Infiltrative disorders
Congenital causes of Primary Hypothyroidism
Thyroid agenesis or dysgenesis
Dyshormogenesis
TSH receptor mutations (inactivating)
Maternal antithyroid hormone therapy (transient)
Maternal TSH receptor antibodies (treatment)
Drugs that cause hypothyroidism
Amiodarone
Lithium
Antithyroid drugs
Interferon alpha
Cause of transient hypothyroidism
Silent thyroiditis (postpartum thyroiditis)
Subacute thyroiditis
Shortly after iodine treatment or subtotal thyroidectomy for Grave’s disease
Hypothyroidism symptoms and signs
Fatigue Generalized weakness Dry skin Cold intolerance Hair loss Difficulty concentrating/poor memory Constipation Weight gain with poor apetite Dyspnea Hoarse voice Menorrhagia (later in the clinical course, oligo or ameno) Paresthesia Impaired hearing
Signs of hypothyroidism
Dry coarse skin; cool peripheral extremities Puffy face, hands, feet (myxedema) Diffuse alopecia Bradycardia Nonpitting peripheral edema Delayed tendon reflex relaxation Carpal tunnel syndrome Serious cavity effusions
Most common symptom of hypothyroidism
Fatigue and generalized weakness
Most common sign of hypothyroidism
Dry, coarse skin, cool peripheral extremities
Laboratory manifestations of hypothyroidism
Normochromic, normocytic anemia Hypercholesterolemia Hyponatremia (in advanced hypothyroidism) Hyperprolactinemia Elevated creatine phosphokinase level Hypoglycemia (myxedema coma)
The first-line diagnostic test for hypothyroidism and patient screening
Serum thyrotropin TSH
An elevated TSH level should be confirmed by
repeated measurement of TSH with FT4
When evaluating thyroid function in suspected hypothalamic/pituitary disease, TSH measurement
is inadequate
May be useful to define underlying cause of primary hypothyroidism although not required in all settings
measurement of antithyroid antibodies
If a patient has sustained hypothyroidism after extensive exclusion of other potential causes, it is presumed to be
autoimmune in origin
Primary hypothyroidism Initial Test
TSH
If normal, exclude primary thyroid abnormality
If elevated, confirm by repeat TSH and FT4
Primary hypothyroidism thyroid function profile
Elevated TSH
Low FT4
Subclinical hypothyroidism
Elevated TSH
Normal FT4
TSH normal and pituitary disease suspected but
low free T4 level
assess for possibility of medication effects or sick euthyroid syndrome
TSH level normal and pituitary disease suspected
Normal free T4
Excludes secondary and tertiary causes of hypothyroidism
Secondary or Tertiary Hypothyroidism Lab profile
TSH level: highly variable usually normal
FT4: LOW
Present in 90-95% of patients with autoimmune hypothyroidism
40-80% of patients with Grave’s
Useful in predicting progression of subclinical to overt hypothyroidism
TPO antibodies
Present in 5-25% of euthyroid women
2% of euthyroid men
Not specific for diagnosis of autoimmune hypothyroidism not indicated for evaluation
Important in management of patients with differentiated thyroid carcinoma
Thyroglobulin autoantibodies
Iodine scan in Hashimoto’s thyroiditis shows
Decreased and heterogenous tracer uptake
When secondary or tertiary hypothyroidism is suspected, this imaging may be employed
MRI of pituitary gland
MRI/CT of the brain if suprasellar process suspected
Biopsy of Hashimoto’s thyroiditis reveal
Lymphocytic infiltration
Follicular destruction
Fibrosis
Treatment of choice for hypothyroidism
Levothroxine
Endocrine emergency treated promptly with thyroid hormone once coexisting adrenal insufficiency is excluded
Myxedema coma
Treatment for overt hypothyroidism
Levothyroxine 1.6 microgram/kg
Starting dose
<60: without CV disease 50-100
in severe: lower end dose recommended
TSH should be checked once started on levothyroxine after
2 months
Goal of TSH level in hypothyroidism
1-2 mIU/L
Multiple levothyroxine products exist.
TSH level should be rechecked after switching to a new product to ensure adequate dosing.
Bioequivalence
In a patient of normal body weight taking >200 ug of levothyroxine with elevated TSH and normal or high FT4 may indicate
poor compliance
Patients who miss doses can be advised to take up to
3 doses of skipped tablets at once owing to long half life
In patients with TSH >4.5 mU/L and positive TPO antibodies
Subclinical hypothyroidism
Patient may be started on
Levothyroxine
If not started, monitor TSH anually
Levothyroxine treatment on Subclinical Hypothyroidism may improve
Left ventricle function
Lipid profile
In patients with history or high risk hypothyroidism who are contemplating pregnancy, they must be rendered
euthyroid before and throughout pregnancy
Thyroid function of pregnant patients should be evaluated once
Pregnancy confirmed
2nd and 3rd trimester
Levothyroxine doses often need to be increased by how much in pregnancy
> /= 30-50%
The dose may be returned to preconception levels postpartum
In elderly persons, dose of thyroxine may be lessened by
20%
If with CAD, starting dose is 12.5-25 ug/d with similar increments every 2 months until TSH is normalized
Minor complications of surgery for hypothyroidism
Intraoperative hypotension Sensitivity to anesthesia Ileus Hyponatremia Central nervous dysfunction
Drugs that interfere with thyroid hormone absorption
Iron Calcium carbonate Cholestyramine Aluminum hydroxide gel Sucralfate Dietary soy
Medical conditions that may interfere with thyroid hormone absorption
GI maladaptive disorders
Previous small-bowel bypass surgery
Postmenopausal hormone therapy requires increase in levothyroxine by
35%
Myxedema coma treatment
Levothyroxine 500 ug
T3 IV (conversion of T3 to T4 is impaired)
Combined levothroxine and T3 as single initial bolus
Daily doses of levothyroxine and T3
Excess T3 may provoke
arrhythmia
Supportive measures for myxedema
Treatment of precipitating factor
Ventilatory support during first 48 hours
Parenteral hydrocortisone (50 mg q6) is indicted for impaired adrenal reserve
Hypertonic saline or intravenous glucose for severe hyponatremia or hypoglycemia
Hypotonic IV avoided
External warming if temperature <30 to avoid cardiovascular collapse
Drug clearance may be impaired
Sedatives should be avoided if possible
Complications associated with untreated hypothyroidism
Increased sensitivity to sedatives, analgesics and anesthetic agents Hypercholesterolemia CAD Diastolic dysfunction and hypertension Decreased sensitivty to warfarin
Painful inflammation of thyroid gland
Self-limited
Transient hyperthyroidism -> hypothyroidism -> euthyroid in a span of
Subacute thyroiditis De Quervain’s thyroiditis Granulomatous thyroiditis Giant cell thyroiditis Viral thyroiditis
Subacute thyroiditis epidemiology
Age
Sex
Season
peaks 30-50 years
Women 3x
Peaks in summer
Patients with subacute thyroiditis often report with
antecedent viral respiratory infection
Subacute thyroiditis predominant HLA
HLA B35
Viruses implicated in Subacute Thyroiditis
Mumps Measles Influenza Coxsackie Adenovirus Echovirus
Painful, mildly enlarged thyroid
Asymmetric
Sore throat with pain to the jaw or ear
Rare cause of chest pain
Acute onset of hyperthyroidism
Fever
Fatigue
Myalgia
Subacute thyroiditis
Thyrotoxic phase of Subacute Thyroiditis
T4, T3 increased
Low TSH
Ratio of T4 and T3 in Subacute Thyroiditis
T3>T4
Inc T4/T3 ratio
Hypothyroid phase of Subacute Thyroiditis
Moderately inc TSH
Low T4,T3
after several weeks thyroid is depleted of stored thyroid hormone
Subacute Thyroiditis
Dx
Tx
Radioiodine uptake and scan to assess
UTZ, FNAB not needed
Symptomatic control of thyroid pain and tenderness and non-specific symptoms
Mitigating the transient effects of hyperthyroidism
Thyroid cancer associated with Hashimoto’s
Primary thyroid lymphoma
