THE INCIDENCE OF THYROID-DISORDERS IN THE COMMUNITY - A 20-YEAR FOLLOW-UP OF THE WHICKHAM SURVEY

BACKGROUND AND OBJECTIVE The original Whickham Survey documented the p revalence of thyroid disorders in a randomly selected sample of 2779 a dults which matched the population of Great Britain in age, sex and so cial class. The aim of the twenty-year follow-up survey was to determi ne the incidence and natural history of thyroid disease in this cohort . DESIGN, PATIENTS AND MEASUREMENTS Subjects were traced at follow-up via the Electoral Register, General Practice registers, Gateshead Fami ly Health Services Authority register and Office of Population Censuse s and Surveys. Eight hundred end twenty-five subjects (30% of the samp le) had died and, in addition to death certificates, two-thirds had in formation from either hospital/General Practitioner notes or post-mort em reports to document morbidity prior to death. Of the 1877 known sur vivors, 96% participated in the follow-up study and 91% were tested fo r clinical, biochemical and immunological evidence of thyroid dysfunct ion. RESULTS Outcomes in terms of morbidity and mortality were determi ned for over 97% of the original sample. The mean incidence (with 95% confidence intervals) of spontaneous hypothyroidism in women was 3.5/1 000 survivors/year (2.8-4 5) rising to 4.1/1000 survivors/year (3.3-5. 0) for all causes of hypothyroidism and in men was 0.6/1000 survivors/ year (0.3-1.2). The mean incidence of hyperthyroidism in women was 0.8 /1000 survivors/year (0.5-1.4) and was negligible in men. Similar inci dence rates were calculated for the deceased subjects. An estimate of the probability of the development of hypothyroidism and hyperthyroidi sm at a particular time, i.e. the hazard rate, showed an increase with age in hypothyroidism but no age relation in hyperthyroidism. The fre quency of goitre decreased with age with 10% of women and 2% of men ha ving a goitre at follow-up, as compared to 23% and 5% in the same subj ects respectively at the first survey. The presence of a goitre at eit her survey was not associated with any clinical or biochemical evidenc e of thyroid dysfunction. In women, an association was found between t he development of a goitre and thyroid-antibody status at follow-up, b ut not initially. The risk of having developed hypothyroidism at follo w-up was examined with respect to risk factors identified at first sur vey. The odds ratios (with 95% confidence intervals) of developing hyp othyroidism with (a) raised serum TSH alone were 8 (3-20) for women an d 44 (19-104) for men; (b) positive anti-thyroid antibodies alone were 8 (5-15) for women and 25 (10-63) for men; (c) both raised serum TSH and positive anti-thyroid antibodies were 38 (22-65) for women and 173 (81-370) far men. A legit model indicated that increasing values of s erum TSH above 2mU/l at first survey increased the probability of deve loping hypothyroidism which was further increased in the presence of a nti-thyroid antibodies. Neither a positive family history of any form of thyroid disease nor parity of women at first survey was associated with increased risk of developing hypothyroidism. Pasting cholesterol and triglyceride levels at first survey when corrected for age showed no association with the development of hypothyroidism in women. CONCLU SIONS This historical cohort study has provided incidence data for thy roid disease over a twenty-year period for a representative cross-sect ional sample of the population, and has allowed the determination of t he Importance of prognostic risk factors for thyroid disease identifie d twenty years earlier.