SCREENING FOR THYROID DISEASE
Case Study
LF, a 50-year-old woman, requests a "thyroid blood test."
You review the symptoms of hypothyroidism and hyperthyroidism with
her and find that she has none of them. She still is concerned
because "a doctor on television said all women should have this
test."
Case Study Questions
1. Based on recommendations from the U.S. Preventive
Services Task
Force (USPSTF), which one of the following
statements should be
considered in LF's care?
A. Physicians should screen all adults for thyroid disease.
B. Physicians should not screen adults for thyroid disease.
C. Evidence is insufficient to recommend for or against
routine
screening for thyroid disease in adults.
D. Physicians should screen high-risk adults for thyroid
disease.
E. Physicians should screen adults older than 50 years
for
thyroid disease.
2. Which one of the following statements about thyroid
screening and
treatment in screen-detected patients is
correct?
A. The thyroid-stimulating hormone (TSH) test can detect
subclinical thyroid disease.
B. Treatment of subclinical thyroid disease improves
clinically
important outcomes in adults with screening-detected
disease.
C. When TSH is used for screening primary care
populations, a
positive screening test result almost always leads to a
diagnosis of thyroid disease.
D. Subclinical hyperthyroidism is more common than
subclinical
hypothyroidism.
E. False-positive tests are less common in elderly
patients.
3. Which of the following statements about adults with
subclinical
thyroid disease are correct?
A. Subclinical hyperthyroidism is associated with atrial
fibrillation, dementia, and osteoporosis.
B. Subclinical hypothyroidism is associated with poor
obstetric
outcomes and poor cognitive development in children.
C. There is clear evidence that adults with subclinical
hypothyroidism have a decreased quality of life.
D. Progression from subclinical to clinical disease in
patients
without a history of thyroid disease is not clearly
established.
Answers
1. The correct answer is C. The USPSTF concluded that the
evidence is insufficient to recommend for or against routine
screening for thyroid disease in asymptomatic adults. The USPSTF
found no controlled studies that examined whether routine
screening for thyroid disease in the primary care setting leads to
improved symptoms or other health outcomes. Although the yield of
screening is greater in certain high-risk groups (e.g., postpartum
women, persons with Down syn- drome, elderly persons), the USPSTF
found poor evidence that screening these groups leads to
clinically important benefits. False-positive test results have
the potential for harm, although the magnitude of harm is not
known. There is good evidence of overtreatment with levothyroxine
in many patients, but the long-term harmful effects of
over-treatment are not known. As a result, the USPSTF could not
determine the balance of benefits and harms of screening
asymptomatic adults for thyroid disease.
2. The correct answer is A. Subclinical thyroid dysfunction
is an abnormal biochemi-cal measurement of thyroid hormones in
patients without specific clinical signs or symptoms of thyroid
disease and with no history of thyroid dysfunction or therapy.
This includes patients with mildly elevated TSH and normal
thyroxine (T4) and tri-iodothyronine (T3) levels (i.e.,
subclinical hypothyroidism) or low TSH and normal T4 and T3 levels
(i.e., subclinical hyperthyroidism). Subclinical thyroid disease
is much more common than overt disease in primary care
populations. Up to 5 percent of women and 3 percent of men have
subclinical hypothyroidism. Subclinical hyperthyroidism occurs in
1 percent of men older than 60 and 1.5 percent of women older than
60.
Screening for thyroid dysfunction can be conducted using
the medical history, physi-cal examination, or any of several
serum thyroid function tests. The TSH test can detect subclinical
thyroid disease. However, when TSH is used for screening primary
care populations, the probability that an abnormal result
represents true disease (i.e., positive predictive value) is
lower. Furthermore, interpretation of a positive test result often
is complicated in certain populations. For example, false-positive
results are more common in elderly patients and in those with a
severe underlying illness.
3. The correct answers are A, B, and D. Subclinical
hyperthyroidism has been asso-ciated with atrial fibrillation,
dementia, and, less clearly, osteoporosis. Subclinical
hypothyroidism is associated with poor obstetric outcomes and poor
cognitive development in children. Evidence for dyslipidemia,
atherosclerosis, and decreased quality of life in adults with
subclinical hypothyroidism in the general population is
inconsistent and less convincing. Progression from subclinical to
clinical disease in patients without a history of thyroid disease
is not clearly established.
