hypothyroidism Flashcards
hypothyroidism
-Iodine deficiency
-Rare in the US
-Remains the MC cause of hypothyroidism worldwide
-In areas of iodine sufficiency
-Autoimmune disease (Hashimoto’s thyroiditis)
-Iatrogenic causes (treatment of hyperthyroidism) are also very common
epidemiology
-Neonatal/congenital hypothyroidism - more often in Caucasian than in African-American infants
-Spontaneous hypothyroidism - European Caucasians > African-Americans
-Genetics- Thyroid development defects are sometimes congenital
-Geography
-Incidence is 10x higher than average in iodine-deficient areas
-Also increased in areas exposed to waterborne goitrogens or where there is excessive consumption of goitrogens (e.g. cassava)
-Incidence is raised in areas exposed to excessive radiation
-More in Japanese – high iodine content & genetic factors
etiology- primary
-Autoimmune hypothyroidism: Hashimoto’s thyroiditis, atrophic thyroiditis -> Hepatitis C and Interferon can put at increased risk
-Iatrogenic: 131I treatment, subtotal or total thyroidectomy, external irradiation of neck for lymphoma or cancer
-Drugs: iodine excess (including iodine-containing contrast media and amiodarone), lithium, antithyroid drugs,
-Congenital hypothyroidism: absent or ectopic thyroid gland, dyshormonogenesis, TSH-R mutation
-Iodine deficiency
-Infiltrative disorders: amyloidosis, sarcoidosis, hemochromatosis etc.
-Overexpression of type 3 deoiodinase in infantile hemangioma
-After 131-I treatment or subtotal thyroidectomy for Graves’ disease
-Transient:
-asymptomatic - deont need to treat
-Silent thyroiditis, including postpartum thyroiditis
-Subacute thyroiditis
-Withdrawal of T4 treatment in pts. with an intact thyroid
etiology: secondary
-Hypopituitarism: tumors, pituitary surgery or irradiation, infiltrative disorders, Sheehan’s syndrome, trauma, genetic forms of combined pituitary hormone deficiencies
-Isolated TSH deficiency or inactivity - rare
-Bexarotene treatment – anti-neoplastic agent
-Hypothalamic disease: tumors, trauma, infiltrative disorders, idiopathic
-TSH levels may be LOW, normal, or even slightly increased in secondary hypothyroidism
-Treatment - maintain unbound T4 levels in the upper half of the reference range, as TSH levels cannot be used to monitor therapy
-Diagnosed in the context of other anterior pituitary hormone deficiencies -> Isolated TSH deficiency is very rare
-Hypothyroidism - due to secretion of immunoactive but bio-inactive forms of TSH
mild thyroid failure
-May be present in cases of:
-Gastrointestinal disease
-Hyperlipidemia
-Coronary artery disease
-Hypertension
iatrogenic hypothyroidism
-Commonest cause of hypothyroidism
-Can often be detected by screening before symptoms develop
-In the first 3 to 4 months after radioiodine treatment, transient hypothyroidism may occur due to reversible radiation damage rather than to cellular destruction
-Low-dose thyroxine treatment can be withdrawn if recovery occurs
chronic iodine excess
-Paradoxically, chronic iodine excess can also induce goiter and hypothyroidism (normally hyper with high iodine)
-Intracellular events - for this effect are unclear
-Individuals with autoimmune thyroiditis are especially susceptible
-Iodine excess responsible for hypothyroidism in up to 13% of patients treated with amiodarone
-Other drugs, particularly lithium, may also cause hypothyroidism
predisposing factors
-More prevalent with increasing age; More prevalent in women
-Autoimmune diseases
-Incidence- 5-10/1000 in general population.
-Prevalence- Prevalence is 50-100/1000 in general population.
-Frequency- Neonatal/congenital hypothyroidism is seen in 0.25/1000 live births
associated autoimmune diseases
-Hypoparathyroidism
-Diabetes Mellitus 1
-Pernicious anemia
-SLE
-Rheumatoid arthritis
-Sjogren’s Syndrome
-Addison’s disease*- must watch bc if you dont give cortisol they will die
-Vitiligo
-Myasthenia gravis
symptoms
-Tiredness, weakness
-Dry skin
-Feeling cold
-Hair loss
-Constipation
-Weight gain with poor appetite
-Dyspnea
-Hoarse voice
-Menorrhagia (later oligomenorrhea or amenorrhea)
-Paresthesia
-Impaired hearing
-Difficulty concentrating and poor memory
signs
-Dry coarse skin; cool peripheral extremities
-Puffy face, hands- Myxedema -> Non pitting edema! (pre-tibial is hyperthyroid)
-Lower extremities – pitting edema
-Diffuse alopecia
-Bradycardia
-Peripheral edema
-Delayed tendon reflex relaxation
-Carpal tunnel syndrome
-Serous cavity effusions
subclinical hypothyroidism
-May be asymptomatic or manifest as:
-Depression
-Cognitive problems
-Weight gain
-Fatigue
-Irregular menstruation
-Infertility
other clinical manifestations
-Insidious onset
-Patient may become aware of symptoms only when euthyroidism is restored
-Hashimoto’s thyroiditis - present with a goiter rather than symptoms of hypothyroidism
-Goiter may not be large
-Usually irregular and firm
-Often possible to palpate a pyramidal lobe (middle part- might be remnant of thyroglossal duct cyst) -> Vestigial remnant of the Thyroglossal duct
diff dx
-Aging
-Congestive heart failure
-Depression
-Accidental hypothermia
-Sick Euthyroid syndrome
-Chronic renal failure
-Down’s Syndrome
-Nephrotic syndrome
-Amyloidosis
-Drug intoxication
evaluation
-High TSH, low T4
-TSH assay and free T4 levels confirm diagnosis -> Free T3 levels - may or may not be useful
-Patients with primary (but not supra-thyroid) clinical or subclinical hypothyroidism have raised TSH levels
-Patients with clinical, overt hypothyroidism have decreased free T4 levels, but only 1/3 of such patients have decreased free T3 levels
-Those with subclinical hypothyroidism can have normal T4 and/or T3 levels
-Serum lipid levels - to detect any dyslipidemia
-CBC - to detect any anemia
-TSH - primary test in diagnosis of hypothyroidism
-Serum levels are raised if the patient has overt or mild primary hypothyroidism but may be normal or low in suprathyroid hypothyroidism
-Free T4 assay: clinical, overt hypothyroid patients have reduced free T4 levels;
-Free T3 assay: only one third of clinical, overt hypothyroid patients have reduced free T3 levels;
thyroid autoantibody
-Thyroid autoantibody (also for graves)
May be performed
-Positive result - in 95% of patients with autoimmune thyroiditis
-Not often employed in clinical decision-making though some use this test to decide whether to treat cases of mild thyroid failure
-May be confirmatory in patients with thyroid tenderness
treatment
-Levothyroxine (T4)
-stick with same supplier for greatest efficacy -> dont switch to synthyroid
-Only recommended treatment
-Usually started at a dose between 25-75mcg, and titrated to target
-Takes 4-6 weeks for TSH blood level to adjust after a change in dose
-Recommended follow-up period
-Liothryonine (Tri-iodothyronine, T3)
-May be prescribed in post-thyroidectomy patients to minimize the amount of time they need to be off thyroid replacement therapy before an iodine scan; not used as mono-therapy
-Patients should be encouraged to eat a high-fiber diet to reduce the risk of constipation and, if obese, to eat a low-fat diet, at least until he/she is euthyroid
follow up
-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 to 3 years, if a normal TSH is maintained over several years
-It is important to ensure ongoing compliance, however, as patients do not feel any difference after missing a few doses of levothyroxine, this sometimes leads to self-discontinuation
summary of hypothyroid
-Common condition caused by inadequate secretion of thyroid hormone
-Hypothyroidism is usually not life-threatening (unless myxedema coma)
-Cardiac enlargement due to dilation and -pericardial effusion (myxedema heart disease) may occur
-Dyslipidemia, a major cause of coronary artery disease
-Serious illness is characterized by non-pitting edema (myxedema) of face and periphery
-Treated by thyroid hormone replacement (levothyroxine)
-Many patients with mild thyroid failure are not diagnosed due to a lack of screening with thyroid-stimulating hormone (TSH) assay among the adult population
-Myxedema Coma - potentially fatal complication
