Prevalence of primary hyperparathyroidism in 13387 patients with thyroid diseases, newly diagnosed by screening of serum calcium.

Primary Hyperparathyroidism (PHP) often goes unrecognised. Evidence of the influence of thyroid diseases on parathyroid activity exists. In order to determine the prevalence of primary hyperparathyroidism (PHP) in patients with thyroid diseases, a series of patients referred to an outpatient department for patients with thyroid diseases were examined for additional PHP. In addition to screening for thyroid diseases, serum calcium concentration (S-Ca) was measured in a series of persons who came to our outpatients' service for patients with thyroid diseases during the period 1992 to 1998. 13387 persons, median age 48 y, m = 2367, f = 11020, among them 9017 patients with thyroid diseases and 4370 persons without thyroid dysfunction, were studied. In patients with S-Ca outside the normal range, further diagnostic tests relating to PHP were performed. 106/13387 persons showed S-Ca > or = 2.6 mmol/L, in 31 cases due to PHP. In comparison to persons without thyroid diseases, the occurrence of PHP was significantly higher in patients with thyroid diseases (4/4370 = 0.09% vs. 26/9017 = 0.29%). Furthermore, 2 patients with normal S-Ca were diagnosed as having PHP in addition to another endocrine disease (acromegaly, multiple endocrine neoplasia type IIa, resp.). 31 of the 54 persons with S-Ca > 2.6mmol/L and who showed no other reasons for hypercalcaemia were found to be in a hyperthyroid state. The prevalence of PHP was significantly higher in patients with euthyroid goitre (p < 0.05) and in patients with thyroid carcinoma (p = 0.01) as compared to other persons with thyroid diseases. The groups of patients did not differ with regard to age. However, patients without thyroid diseases were significantly younger (median age 38y). Above the age of 50, the prevalence of PHP became higher in patients with euthyroid goitre or thyroid carcinoma than in those with a healthy thyroid gland. In contrast, in persons of under 50 y, there was no difference between these groups. The percentage of males with PHP was higher than in the total population studied (30% vs. 21.5%). In conclusion, a high occurence of PHP could be demonstrated in patients with thyroid diseases (0.29%) as compared to persons without thyroid dysfunction (0.09%), the highest prevalence being in patients with thyroid carcinoma. A clinically not relevant influence of thyroid function on S-Ca was seen in some patients with hyperthyroidism. Determination of S-Ca is recommended for each patient referred to a thyroid outpatients' department because of the high number of PHP cases in this context.