The relationship between adenoma weight and intact (1–84) parathyroid hormone level in primary hyperparathyroidism

The Relationship Between Adenoma Weight and Intact (l-84) Parathyroid Hormone Level in Primary Hyperparathyroidism J. Graham Williams, BS~, iwh, FRCS, Malcolm H. Wheeler, Richard C. Brown, BSc, PhD, J. Stuart Woodhead, BSc, PhD,

The relationship between preoperative serum levels of intact ,parathyroid hormone (PTH) , serum calcium, and the weight of parathyroid adenoma has been investigated in 44 patients undergoing surgery for primary hyperparathyroidism due to single glaxid d$ease. There was no significant correlation betwqen preoperative serum calcium and either intact pl?r concentration or adenoma weight (r = 0.465 and 0.381, respectively). Although there was a &n&ant correlation between PTH concentration and adenoma weight (r = 0.850, p <0.0005), this correlation was lost when two unusually heavy adenomas weighing 10.98 and 15.23 g were removed from t+e analysis. Clearly, a preoperative direct prediction of gland weight determined from PTH level was not possible. Patients with adenomata heavier than 750 mg had a significantly lower circulating PTH level per mg of adenoma than patients with glands lighter than 750 mg. PTH secretion in vitro in low calcium medium by adenoma cells from glands weighi@ less than 1 g was higher than secreiion by cells from adenomas heavier than I g. Larger parathyroid adenomata appear to secrete less PTH per unit weight in uivb and per unit cell in vitro under conditions of maximal stimulation.

From the Departments of Surgery (JGW, MHW), and Medical Biochemistry (JPA, RCB. JSW), University of Wales College of Medicine, Cardii, Wales, United Kingdom. Requests for reprints should be addressed to Malcolm H. Wheeler, MD, Department of Surgery, University HaPpita of Wales, Heath Park, Cardii CF4 4XN, Wales, United Kingdom. Manwzri~submittedSeptember21,1990,andacceptedin revised fom February 8.1991.

MD, FRCS, MRCPath,

J. Paul Aston,

Cardiff.

BSC,

PhD,

Wales, United Kingdom

I

n 80% of patients with primary hyperparathyroidism, a single adenoma is the cause of the hypercalcemia. Surgical exploration, with excision of the adenomatous parathyroid gland, is the accepted treatment [I,21 However, 3% to 17% of patients with primary hyperparathyroidism have a second enlarged gland, and 15% to 20% have four-gland hyperplasia [3-a. A preoperative guide to the amount of abnormal parathyroid tissue present would assist the surgeon and reduce the chance of leaving pathologic parathyroid tissue in the patient. Previous attempts to correlate weight or volume of parathyroid adenoma with preoperative serum calcium or parathyroid hormone (PTH) levels have yielded variable results [7-121. The development of a sensitive and specific assay of intact (l-84) PTH in our laboratory [Z3] has facilitated studies on PTH release in vivo and in vitro. We have examined the relationship between adenoma weight and the circulating level of intact PTH to assess whether the preoperative intact PTH concentration is a guide to the amount of abnormal parathyroid tissue present.

.

PATIENTS AND METHODS In Go studies: Forty-four

patients who underwent parathyroidectomy for primary hyperpamthyroidism as a result of a single parathyroid adenoma were studied. There were 36 women and 8 men, and their ages ranged from 23 to 87 years (median age: 60 years). Each patient had serum calcium, albumin, urea, creatine, phosphate, and alkaline phosphatase measured by auto-analysis in the routine biochemistry laboratory. All patients had urea and creatine levels within the normal range. Serum calcium was corrected for an albumin level of 40 g/L by adding or subtracting 0.02 mmol/L for each g/L of albumin deviation. Intact (l-84) PTH level was measured in each patient as described previously [13]. In this method, a sample is incubated first with an N-terminal specific antibody labeled with a chemiluminescent acridinium ester and sub sequently with a C-terminal specific antibody linked to paramagnetic particle. The bound immune complex containing only intact PTH molecules is quantified in a luminometer (Ciba Coming Diagnostics, Medfield, MA). The sensitivity of this method is 0.2 pmol/L, and the dose response is linear between 0.8 and 200 pmol/L. Each patient underwent cervical exploration. The adenomatous parathyroid gland was identified, and an attempt was made to identify the three other normal glands. The adenoma was carefully excised intact, and a small biopsy was taken from one of the remaining normal parathyroid glands. The two samples were transported to

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.

.

3.6

.

1

r=0.465 ns

3.4

3.6

.

r=0.361 ns

I

. .

IO

20 l-64

Figure

1. RelaHonship

30

40

50

.

60

160

160

0

200

400

b6twe6f1

600

600

1000

1200

1400

1600

Adenoma weight mg.

PTH pmolll

preoperative serum calcium Flgure 2. Relationship between preoperative serum calcium

(Ca++) and intact l-84 pafathyroid hormone (PTH) conwntmtkns. NS = not signifkant.

(Ca++) wncentration and adenoma weight. NS = not significant.

the pathology laboratory where the adenoma was weighed on a chemical balance, and cryostat sections were made of both samples. The diagnosis of parathyroid adenoma was confiimed by paraffin sections. In all 44 patients, serum calcium and intact PTH levels returned to normal following parathyroidectomy. IO v&o studies: Secretion of intact PTH by cells from 10 parathyroid adenomas weighing 0.15 to 8.7 g was measured. Adenomas were placed immediately into ice cold Eagle’s minimum essential medium containing 20 mM HEPPS (N-2-hydroxyethyl-piperazine-N’-2-ethanesulfonic acid), 1 mM MgS04, and 1 mM CaC12(pH 7.4). Dispersed cell samples were prepared by enzymic digestion in collagenase and DNAase [14]. Erythrocytes and fat were removed by centrifugation, and the parathyroid cells were washed in fresh culture medium. Viability was assessed by exclusion of trypan blue. Two to five X lo5 parathyroid cells/ml were incubated in culture medium containing 0.05 mm01 calcium at 37’C for 120 minutes. After centrifugation, intact PTH was measured in the medium, and hormone release was expressed in pmol/ lo5 cells/hr. Analysis: The relationship between adenoma weight, circulating intact PTH level, and serum calcium was investigated by calculating Pearson correlation coeflicients between each of these variables.

between the level of intact PTH and the weight of adenoma excised (r = 0.85, p = 0.0005) (File 3), but this analysis was significantly influenced by two unusually heavy adenomas that weighed 10.98 and 15.23 g. When these were removed from the analysis, correlation was lost and an r value of 0.28 was achieved. The relationship between the level of circulating intact PTH and adenoma weight was examined further by calculating the ratio of intact PIH per gram of adenoma excised. This ratio was significantly lower in patients who had adenomas heavier than 750 mg excised than patients who had adenomas lighter than 750 mg (p
RESULTS

In tivo studies: The median preoperative level of serum calcium was 2.82 mmol/L (interquartile range: 2.73 to 2.93 mmol/L). The median preoperative level of intact PTH was 23.2 pmol/L (range: 15.5 to 33 pmol/L). The highest level of PTH was 177.4 pmol/L. The weight of parathyroid adenomata subsequently excised ranged from 140 mg to 15.23 g (median weight: 760 mg). There was no correlation between the level of serum calcium and intact PTH (r = 0.465) (Fv 1). Similarly, there was no correlation between the level of serum calcium and the weight of the adenoma subsequently excised (r = 0.381) (Figure 2). There was a correlation 302

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Persistent primary hyperparathyroidism may ensue when multiglandular disease is not recognized during parathyroidectomy. A preoperative guide to the expected quantity of abnormal parathyroid tissue present in a patient with primary hyperparathyroidism would be of considerable value to the surgeon. Previous authors have attempted to demonstrate a relationship between adenoma size and either calcium level or PTH level with variable results. Positive correlation between PTH level, measured by radioimmunoassay, and either adenoma weight or volume has been reported [7-9,121, as well as between serum calcium and gland size [ 7-91 and serum calcium and PTH levels [I 21.

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RATIO OF CIRCULATING TO ADENOMA

INTACT PTH

WEIGHT

SMALL vs LARGE ADENOMAS

1601

. 0.12-

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Adenoma weight mg F@w

*

3. Fblationship between pmoperative intact l-84 pamthy-

rold hormons (PlH) concentretionand wei$bt of dsfloms exciaed(r=0.85,p=0.0005).~whenthetwoheaviegtgland ~areremovsdfromtheanalysissignificsnceisbst(r=

.

2s

<75Omg

.

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F@ma 4. Intact l-84 pglgthyroidhormone (Pm) cancentration

expressdasaftmctkmofadsnamawei@t.~w8ighing However, other studies have not shown any correlation between these variables [IO,1I]. Most of the above stud- lessthsn750mgsecfetdsignificantlymorePn-lpermg0f z,p kser glands weighing more m 750 mg (P ies have relied upon either N- or C-terminal FTH assays with all the potential problems of inadequate assay sensitivity and specificity. In the present study, a sensitive and specitic assay of the regulatory defects present in the two types of lesions. intact (l-84) PTH has been used. This assay simplifies Clearly, from the results of these studies, there are also the diagnosis of primary hyperparathyroidism as there is differences within a population of adenomas. clear separation between normal subjects, patients with One explanation for the apparent lower release of primary hyperparathyroidism, and those with hypercal- PTH from larger adenomas may be the smaller proporcemia of malignancy [Z5]. We were unable to demon- tion of FTH secreting cells in larger adenomas resulting strate a correlation between the level of intact PTH and from a greater proportion of the adenoma being comthe weight of adenoma excised when we examined glands posed of cystic spaces or hemorrhage into the gland. It is weighing between 140 mg and 8.7 g. Therefore, direct not known if all the cells in a parathyroid adenoma sepreoperative prediction of adenoma size is not reliable as crete PTH at the same rate or whether the rate of secrea patient with an intact FTH level of 20 pmol/L could tion varies from cell to cell. Studies in our laboratories, have an adenoma weighing 200 to 1,200 mg. Thus, the using immunohistochemistry, have shown that staining intact PTH level can only be an approximate guide to the for F’TH is not uniform throughout a parathyroid adenosize of the adenoma present, and the surgeon must still ma (B Jasani, personal communication). endeavor to identify all four parathyroid glands at surgery. In summary, the results of the present studies show Of interest is the finding that the level of PTH per mg that the relationship between preoperative PTH level and of adenoma excised was significantly lower for adenomas adenoma weight is too variable to be of practical value to heavier than 750 mg than for those lighter than 750 mg. the surgeon in the planning of surgical strategy. There is This suggests that FTH release from large adenomas indeed no substitute for meticulous and thorough surgical occurs at a lower rate than from smaller adenomas. This exploration in patients with primary hyperparathyroidis supported by in vitro studies on dispersed cell preparaism. tions showing cells from heavier glands releasing PTH at a lower rate than cells isolated from small adenomas. It is This paper reconfirms the lack of a precise preoperaknown that cells derived from hyperplastic parathyroids tive serum assay to guide the surgeon as to the extent of release more FTH than adenomata cells and are more parathyroid tissue excision and re-emphasizes the need easily suppressed by a high calcium environment [15,16]. to try to identify all four parathyroid glands in a thorThese observations point to fundamental differences in ough neck exploration. THE AMERICAN

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