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SUBCLINICAL HYPOTHYROIDISM

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Elevated serum TSH associated with normal total or free T4 ... 9% reverted to normal TSH level. Progression: 3-18% per year. Strongest Predictors of Progression ... – PowerPoint PPT presentation

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Title: SUBCLINICAL HYPOTHYROIDISM


1
SUBCLINICAL HYPOTHYROIDISM
  • Chou Chien-Wen M.D.
  • Division of Endocrinology and Metabolism
  • Chi-Mei Medical Center

2
Definition
  • Elevated serum TSH associated with normal total
    or free T4 and T3 values
  • Mild thyroid failure, compensated, early, latent,
    mild, minimally symptomatic and preclinical
    hypothyroidism
  • Extended the definition subjects with normal FT4
    and TSH, but exaggerated TSH responses to TRH

3
Prevalence
  • 1-10 general population
  • Risk of developing SH increases with female
    gender, advanced age and greater dietary iodine
    intake
  • 7-26 in elderly

4
Half-life of Thyroid Hormones
  • T4 7 days
  • T3 1 day
  • TSH lt 1 hour

5
Natural History
  • 154 female patients 10 years
  • 57 continued mild thyroid failure
  • 34 progressed to overt hypothyroidism
  • 9 reverted to normal TSH level
  • Progression 3-18 per year

6
Strongest Predictors of Progression
  • Antithyroid antibodies
  • Serum TSH gt 20 uU/ml
  • History of radioiodine ablation for Graves
    disease
  • History of external radiation for nonthyroid
    malignancies
  • Chronic lithium treatment

7
Clinical manifestations
  • Often asymptomatic 30 have symptoms
  • Colorado Thyroid Disease prevalence Study
  • 2336 subjects with mild thyroid failure
  • Dry skin, poor ,memory, slow thinking, muscle
    weakness, fatigue,muscle cramps, cold
    intolerance, puffy eyes, constipation and
    hoarseness

8
Swiss Study
  • 323 women hypothyroidism
  • 24 of 93 subjects with mild thyroid failure
    exhibited typical symptoms of hypothyroidism

9
Neurobehavioral Abnormalities and Neuromuscular
Function
  • Depression, Memory loss, Cognitive impairment
  • Peripheral nerve dysfunction decreased
    conduction amplitude in peripheral nerves and an
    abnormal stapedial reflex
  • Skeletal muscle abnormalities including elevated
    serum CPK, increased circulating lactate levels
    during exercise and repetitive discharges on
    surface EMG

10
Cardiac-pulmonary Function
  • Impaired myocardial contractility and diastolic
    dysfunction at rest or with exercise
  • Impairment of exercise-related stroke volume,
    cardiac index and maximal aortic flow velocity
  • Pulmonary testing Decreased vital capacity,
    reduced anaerobic thresholds and decreased oxygen
    uptake at the anaerobic threshold

11
Cardiovascular Risk Factor
  • Increased serum levels of TC and LDL
  • Reduced HDL
  • Increase in the serum TSH level of 1 uU/ml is
    associated with a rise in serum TC of 3.5 mg/dl
    in women and 6.2 mg/dl in men
  • Rotterdam Study increased prevalence of aortic
    atherosclerosis and MI
  • Independent and equivalently important risk
    factor for MI

12
Benefits of Treatment
  • Symptoms
  • Neurobehavioral abnormalities and neuromuscular
    function
  • Cardio-pulmonary function
  • Cardiovascular risk factor

13
Treatment Goals
  • High normal TSH values associated with modest
    increases in cholesterol levels
  • Endothelial dysfunction
  • Optimal goal TSH range for L-thyroxin-treated
    patients is 0.5-2 uU/ml

14
Summary
  • Mild thyroid failure particularly those who have
  • Symptoms
  • Other cardiovascular risk factors
  • Goiters
  • Positive antithyroid antibodies
  • Who are pregnant

15
Whickham Survey
  • Most extensive longitudinal study
  • No association between SH and ischemic heart
    disease

16
Five Distinct Situations
  • Mild unrecognized thyroid failure
  • Undertreated overt hypothyroidism
  • Overtreated overt hyperthyroidism
  • Transient disturbances of thyroid axis
  • Euthyroid outliers

17
Epidemiology of SH
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