CTF Structured Abstract: Screening for Thyroid Disorders/Cancer

Canadian Task Force on Preventive Health Care

Structured Abstract

Please note: In 2003, the CTF updated its Grades of Recommendations to include an "I Recommendation" for situations where insufficient evidence exists to allow a recommendation to be made. (Formerly, these situations were captured under a "C Recommendation".) This change is not retroactive, and all "C Recommendations" made prior to 2003 have not been reevaluated in light of the new "I" recommendation grade. For a discussion of these recommendation grades, please link to the 2003 article in the Canadian Medical Association Journal here.

Screening for Thyroid Disorders and Thyroid Cancer in Asymptomatic Adults

Prepared by Marie-Dominique Beaulieu, MD, MSc, FCFP, Associate Professor of Family Medicine, University of Montreal, Quebec, drawing from materials prepared for the U.S. Preventive Services Task Force

These recommendations were finalized by the Task Force in January 1994

Objective
Burden of Suffering
Options
Outcomes

Evidence
Values
Benefits, Harms, and Costs
Recommendations

Validation
Sponsors
Selected References

Objective

To make recommendations about screening for thyroid disorders (hyperthyroidism and hypothyroidism) and thyroid cancer in asymptomatic adults in Canada. Subclinical thyroid conditions are defined by abnormal thyroid stimulating hormone (TSH) levels, upper- or lower-normal range results of thyroid function tests and absence of symptoms. This updates a 1990 Task Force Report.

Burden of Suffering

Hyperthyroidism and Hypothyroidism

The definitions of what constitute "asymptomatic" hyperthyroidism and hypothyroidism are far from clear. Overt hyperthyroidism and hypothyroidism are defined as a triad of the classical signs and symptoms of thyroid dysfunction, abnormal TSH levels, and abnormal thyroid function tests (TT4, FT4, etc). Sub-clinical conditions are defined by the presence of abnormal TSH levels, thyroid function test results in the upper or lower normal ranges, and the absence of symptoms. However, the signs and symptoms of hypothyroidism and hyperthyroidism are very vague in nature, insidious, and are often attributed by patients to normal aging. Community surveys have reported prevalence rates of overt hyperthyroidism of less than 1.9%, the rates being comparable in elderly populations. If "sub-clinical" cases are included, the prevalence rate can be as high as 2.7%. The prevalence of hypothyroidism in an unselected community population of young, middle-aged and elderly individuals is about 1.4%.

Thyroid Cancer

Cancer of the thyroid represents 1.5% of cancers in women and 0.5% of cancers in men. In 1990, this cancer was responsible of the death of 113 Canadians, 41 males and 72 females. Cancer of the thyroid includes several cell types: papillary and follicular carcinomas, which are rarely fatal with appropriate treatment, and anaplastic carcinoma, which is one of the most lethal of all cancers.

Options

To screen or not to screen for hyperthyroidism and hypothyroidism using basal TSH levels by immunoradiometric assays and for thyroid cancer using neck palpation. Diagnostic measures such as circulating T4 levels, ultrasonography, scintigraphy and needle aspiration were deemed inappropriate for screening purposes. Treatment of mild and sub-clinical hypothyroidism involves T4 replacement therapy.

Outcomes

Sensitivity and specificity of screening measures; cardiac function indicators (e.g., systolic interval, resting heart rate, sodium secretion, serum lipid levels, nerve conduction velocities); 5-year cancer survival rates.

Evidence

MEDLINE was searched for the years 1989 to 1993 using the keywords "hyperthyroidism" and "hypothyroidism" with the subheadings "screening" and "prevention and control". Only original articles were included, with priority given to those with the highest levels of supporting evidence (see below). 12 new articles were identified. Other data sources included materials prepared for the 1989 U.S. Preventive Services Task Force (USPSTF).

Recommendations were graded as:

A Good evidence to support the recommendation that the condition be specifically considered in a PHE.

B Fair evidence to support the recommendation that the condition be specifically considered in a PHE.

C Poor evidence regarding inclusion or exclusion of the condition in a PHE, but recommendations may be made on other grounds.

D Fair evidence to support the recommendation that the condition be specifically excluded from consideration in a PHE.

E Good evidence to support the recommendation that the condition be specifically excluded from consideration in a PHE.

Quality of evidence was rated according to 5 levels:

I Evidence from at least 1 properly randomized controlled trial (RCT).

II-1 Evidence from well-designed controlled trials without randomization.

II-2 Evidence from well-designed cohort or case-control analytic studies, preferably from more than 1 centre or research group.

II-3 Evidence from comparisons between times or places with or without the intervention. Dramatic results in uncontrolled experiments could also be included here.

III Opinions of respected authorities, based on clinical experience, descriptive studies or reports of expert committees.

Values

The 13-member Task Force of experts in family medicine, geriatric medicine, pediatrics, psychiatry and epidemiology used an evidence-based method for evaluating the effectiveness of preventive health care interventions. Recommendations were not based on cost-effectiveness of options. Patient preferences were not discussed.

Background papers providing critical appraisal of the evidence and tentative recommendations prepared by the chapter author were pre-circulated to the members. Evidence for this topic was presented and deliberated upon in 1- to 2-day meetings, 2 to 3 times per year from January 1993 to June 1993. Consensus was reached on final recommendations.

Benefits, Harms, and Costs

Immunoradiometric TSH assays have a reported sensitivity of 80% to 100% and a specificity of almost 100% for early detection of subclinical hyperthyroidism or hypothyroidism.

No RCTs exist on the effectiveness of screening for subclinical hypothyroidism in the general population. 2 RCTs on the effectiveness of early treatment of subclinical hypothyroidism in women reported some improvements in well-being, and a statistically significant increase in systolic interval (an index of cardiac function); however, study designs limit generalizability of these findings. A small trial of 22 women with confirmed subclinical hypothyroidism reported clinical benefits in 25% of participants. Latrogenic hyperthyroidism is a potential adverse effect of treatment, and can lead to angina or atrial fibrillation in susceptible individuals.

The effectiveness of treatment of subclinical hyperthyroidism has not been evaluated.

As a screening measure for thyroid cancer, neck palpation has poor sensitivity (15%) and a specificity of 100% when compared with ultrasonography. Effectiveness of screening has not been evaluated, although 5-year survival rates are better for patients with earlier stage cancer.

Recommendations

Recommendation grade [A, B, C, D, E] and level of evidence [I, II-1, II-2, II-3, III] are indicated after each recommendation. Citations in support of individual recommendations are identified in the guideline text.

Poor evidence exists to include or exclude (from the PHE) screening of postmenopausal women for hypothryoidism or hyperthyroidism using clinical examination or TSH immunoradiometric assays [C, III, I]. However, because of the high prevalence of thyroid disorders in perimenopausal women, clinicians should maintain a high level of clinical suspicion in this group [C, I].
Poor evidence exists to include or exclude screening of asymptomatic adults for thyroid cancer using neck palpation [C, III].

Validation

This report was externally peer-reviewed. Recommendations are consistent with those of the 1989 USPSTF.

Selected References

Source Document

Beaulieu MD. Screening for thyroid disorders and thyroid cancer in asymptomatic adults. In: Canadian Task Force on the Periodic Health Examination. Canadian Guide to Clinical Preventive Health Care. Ottawa: Health Canada, 1994; 612-18.

Other

Canadian Task Force on the Periodic Health Examination: The periodic health examination, 1990 update: 1. Early detection of hyperthyroidism and hypothyroidism in adults and screening of newborns for congenital hypothyroidism. Can Med Assoc J. 1990;142:955-61.

Link to Full Text of this review

Link to Summary Table of Recommendations of this review

Link to Selected References list of this review

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A	Good evidence to support the recommendation that the condition be specifically considered in a PHE.
B	Fair evidence to support the recommendation that the condition be specifically considered in a PHE.
C	Poor evidence regarding inclusion or exclusion of the condition in a PHE, but recommendations may be made on other grounds.
D	Fair evidence to support the recommendation that the condition be specifically excluded from consideration in a PHE.
E	Good evidence to support the recommendation that the condition be specifically excluded from consideration in a PHE.

I	Evidence from at least 1 properly randomized controlled trial (RCT).
II-1	Evidence from well-designed controlled trials without randomization.
II-2	Evidence from well-designed cohort or case-control analytic studies, preferably from more than 1 centre or research group.
II-3	Evidence from comparisons between times or places with or without the intervention. Dramatic results in uncontrolled experiments could also be included here.
III	Opinions of respected authorities, based on clinical experience, descriptive studies or reports of expert committees.