Hypothyroidism Flashcards
most common cause
Hashimoto’s disease
hypothyroidism results in
generalized slowing down of metabolic process
in Hashimoto’s B and T cells
infiltrate the gland as a result of genetic or environmental changes
B and T cell infiltration results in
cell destruction by necrosis or induced apoptosis
atrophic thyroiditis
cytokines released by T cells as well as native thyroid cells propagate the destructive process
cytokine therapy (IFN-alpha) is associated with
increase autoimmune thyroid disease
what antibodies are present in atrophic thyroiditis
antibodies to TPO and thyroglobulin (useful markers of disease), possible TSH antibodies also
TSH receptor antibodies in atrophic thyroiditis
prevent stimulation of TSH
iatrogenic hypothyroidism follows
exposure to radiation or surgery for treatment of hyperthyroidism or head and neck cancers
iatrogenic hypothyroidism usually occurs within
3-12 months after I131 and within 1 month of the following surgery
most common cause of hypothyroidism worldwide
iodine deficiency
pituitary disease and hypothalamic disease can cause
secondary hypothyroidism
an increase in TSH is
the first sign of primary hypothyroidism
T3 levels in hypothyroidism
will often remain in the normal level despite decreased T4
primary hypothyroidism lab values
increased TSH
decreased T4
secondary hypothyroidism lab values
normal to decreased TSH
decreased T4
subclinical hypothyroidism lab values
mildly increased TSH
normal T4
levothyroxine
its synthetic T4, results in a pool thyroid hormone that is readily and consistently converted to T3
levothyroxine is DOC because
chemically stable, low cost, no antigenicity, and uniform potency
half life of levo
7 days
absorption of levo
40-80%, effected by food and some medications
distribution of levo
predominantly protein bound
contraindications of levothyroxine
untreated thyrotoxicosis, acute MI, and untreated adrenal insufficiency
precautions of levothyroxine
NTI, elderly, CV disease, and mucosal disease
levothyroxine drug interactions - increased absorption from GI tract
cholestyramine, calcium carbonate, sucralfate, aluminum hydroxide, ferrous sulfate, dietary fiber supplements
levothyroxine drug interactions - increased T4 clearance
carbamazepine, phenytoin
levothyroxine drug interactions - blocked conversion of T4 to T3
amiodarone
IV dosage forms of levothyroxine
200 mcg and 500 mcg vials
IV to PO conversion of levothyroxine
IV * 1.33
new dose of levothyroxine at about
every 12 mcg
levothyroxine average maintenance dose for most adults around
125 mcg/day
levothyroxine starting dose for healthy adults
50 mcg/day; increase by 25-50 mcg q6-8 weeks
levo; most recent guidelines suggest
1.6 mcg/kg/day as a starting dose in younger, healthy people
levo starting dose for elderly
25 mcg/day; increase by 12.5-25 mcg
levo dose requirements may increase during _____ and decrease _____
pregnancy; with age
levothyroxine should be
taken on an empty stomach and separated from other medicates by at least one hour
complete resolution of symptoms may take
several months, should see improvement in 2-3 weeks
liothyronine
synthetic T3
liothyronine is generally reserved for
myxedema or nontoxic goiter - when rapid therapy is needed to rapidly suppress TSH
disadvantages of liothyronine
short half life - fluctuations in hormone concentrations; divided daily dosing usually required
higher incidence of cardiac adverse effects
Liotrix
attempts to mimic natural secretion; 4:1 ratio of T4:T3
disadvantages in liotrix
expensive, lack of therapeutic rationale, not used anymore
desiccated thyroid is extracted from
hog, beef, or sheep thyroid gland
desiccated thyroid is generally reserved for
those who insist on natural product or feel that synthetic levothyroxine has stopped working for some reason
disadvantages of desiccated thyroid
standardized but unpredictable amount of hormone in each tablet, unpredictable patient response, may be antigenic in allergic or sensitive patients
monitor TSH at least
q6-8 weeks until patient is euthyroid, then at least annually
FT4 can be used to determine
adherence or malabsorption
TSH and monitoring
not helpful in monitoring patients with secondary hypothyroidism
subclinical hypothyroidism
patients may or may not present with symptoms, guidelines recommend to treat only if patient is experiencing symptoms
hypothyroidism during pregnancy leads to
increased rate of still-births and possibly lower psychological scores in infants born by women with inadequate thyroid hormones
thyroid hormones must come from mother during
first 2 months of gestation
pregnancy dosing of levothyroxine
may increase as much as 25-50%
pregnancy and TSH
TSH should be monitored, minimally, at the end of the first and second trimester
myxedema coma
end stage of uncontrolled hypothyroidism, needs to be treated in ICU and has a mortality of 60-70%
clinical features of myxedema coma
hypothermia, advanced stages of hypothyroid symptoms, delirium/coma
patients with myxedema coma usually require
intubation and mechanical ventilation
treatment of myxedema coma
IV T4 300-500 mcg, then 75-100 mc daily, switch to PO
supportive treatment of myxedema coma
IV steroids and fluids
with treatment of myxedema coma
improvements in consciousness/TSH/vital signs are expected within 24 hours
