Epidemiology

Epidemiologic data on the prevalence of primary HPT are sparse for most countries. An autopsy study of a Swedish population revealed parathyroid adenoma in 2.4% and "subclinical" disease represented by micronodular chief cell hyperplasia in another 7%, with an apparent continuum of abnormality ranging from hyperplastic micronodular lesions to the adenomas.7 Borderline hypercalcemia could be clinically detected in occasional patients with hyperplastic glands containing larger, predominant nodules or in those with tiny adenomas, whereas more marked elevation of serum calcium was associated with adenomas of more conspicuous size.7 The histologic abnormalities were particularly common in older individuals of both genders and related to histologic signs of nephrosclerosis, even in the absence of clinically detectable renal dysfunction.7 These findings substantiate the presence of prevalent subclinical and clinical parathyroid disease within the elderly Swedish population. They also mirror problems in clinical management of patients with primary HPT because an increased incidence of micronodular hyperplasia and tiny adenomas has been encountered when patients with borderline hypercalcemia have been liberally submitted to parathyroid exploration.8"10

Population screening has confirmed the prevalence of parathyroid disease in Sweden, but it has also demonstrated that prevalence data depend on the age of the population studied as well as the level of hypercalcemia that is used to distinguish patients with HPT from normal individuals.11"13 Accurate screening for detection of hypercalcemia also requires that repeated serum calcium determinations be used in such surveys.11'13

A health screening survey of employees aged 20 to 63 years within Stockholm County in Sweden included repeated measurements of serum calcium and revealed hypercalcemia supposedly resulting from HPT, with an overall prevalence of 0.4% to 0.6%." Elevated serum calcium levels were detected in approximately 0.3% of men and 1% of women older than 50 years. This screening used serum calcium levels greater than 2.65 mmol/L (10.6 mg/dL) to define hypercalcemia, and older age groups, in which HPT is in fact most common, were not included.

In another health screening survey in Gavle County of Sweden, 16,401 individuals had repeated serum calcium determinations over a 2-year period (1969 and 1971).13 Altogether, 172 individuals were found to have hypercalcemia, with serum calcium levels higher than the normal reference of 2.60 mmol/L on both occasions, without other obvious reasons such as vitamin D or oral calcium medication or malignancy.13 This corresponded to approximately 1% of the population, 0.3% of men and 1.6% of women.

In women older than 60 years, the prevalence of hypercalcemia was close to 3% (Fig. 41 -l).13-14 Female predominance in screening surveys may be partly related to significantly higher normal means of serum calcium in postmenopausal women than in men of the same age, implying that even minimal increases in serum calcium could be more easily detected.13 This probably does not explain a female overrep-resentation in clinically detected HPT, which is also likely to be related to regulatory disturbances within the diseased parathyroid tissue. Although most of the hypercalcemic individuals in this study did not have a parathyroid operation and the diagnosis is not undisputable, it is reasonable to assume that the majority of them had HPT.1314

In a population screening in which serum calcium levels were determined in conjunction with a mammographic health survey, a comparable prevalence of HPT of 2.2% was found for postmenopausal women with a mean age of 59 years.15 The majority of hypercalcemia cases were borderline, and most of the individuals were elderly. Similar high prevalence estimates of hypercalcemia and presumable HPT were documented in a more recent health screening survey from Norway.16 Although figures depend on definition criteria, the disease can be expected in at least 2% of postmenopausal women.1516 Reports from the United States and Europe have suggested that the incidence of HPT may be declining, perhaps because of more restricted use of multichannel screening tests for hypercalcemia.15'17'18

Comparison of health survey figures and hospital statistics in Sweden and the United States indicates that even if surgery were done for relatively liberal indications, currently only about one tenth of all patients with HPT in the population are subjected to parathyroidectomy.1319'20 Considering the high prevalence figures of the health surveys, it is reasonable that studies aim to clarify whether surgery for primary HPT is also of benefit for patients with a mild, asymptomatic, and uncomplicated disease or whether such patients may be safely monitored without surgery.

Per million

FIGURE 41-1. Prevalence of hypercalcemia in men and women of different age groups in the Gavle County Health Survey. (Adapted from Palmar M, Jakobsson S, Akerstrom G, et al. Prevalence of hypercalcemia in a health survey: A 14-year follow-up of serum calcium levels. Eur J Clin Invest 1988;18:39. Copyright 1988 by Blackwell Science Ltd.)

Per million

FIGURE 41-1. Prevalence of hypercalcemia in men and women of different age groups in the Gavle County Health Survey. (Adapted from Palmar M, Jakobsson S, Akerstrom G, et al. Prevalence of hypercalcemia in a health survey: A 14-year follow-up of serum calcium levels. Eur J Clin Invest 1988;18:39. Copyright 1988 by Blackwell Science Ltd.)

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