the parathyroid glands in multiple endocrine neoplasia type 2b

The Parathyroid Glands in Multiple EndocrineNeoplasia Type 2b

J. Aidan Carney, MD, PhD, Sanford 1. Roth, MD, Hunter Heath Ill, MD,Glen W. Sizemore, MD, and Alvin B. Hayles, MD

The histologic features of 21 parathyroid glands obtained from 16 Mayo Clinic patientsaged 2 to 52 years who had multiple endocrine neoplasia type 2b (MEN 2b) were eval-uated. The findings were correlated with the patients' ages and with the serum concentra-tions of calcium (15 patients), phosphorus (14 patients), and immunoreactive parathyroidhormone (iPTH) (11 patients), and with the response of serum iPTH to calcium infusion(6 patients). We also studied the histologic features of 13 parathyroid glands obtainedfrom 8 patients not seen at the Mayo Clinic with MEN 2b. The microscopic appearanceof the glands was normal in patients under the age of 17; with increased age, the glandsdid not exhibit normal involution, and an appearance consistent with mild chief-cell hy-perplasia was evident. This abnormality was not associated with clinical or laboratorymanifestations of hyperparathyroidism. We presently believe that parathyroidectomy forthe disorder is not justified. (Am J Pathol 1980, 99:387-398)

IN 1968, Steiner et al ' proposed the designation "multiple en-docrine neoplasia, type 2" for the familial combination of medullarythyroid carcinoma (MTC), pheochromocytoma, and parathyroid disease.Subsequently, Chong et al 2 pointed out that familial MTC and pheochro-mocytoma occurred in two phenotypically distinct groups of patients. Inone, the patients had a normal appearance and parathyroid disease wascommon; they suggested that this disorder be designated "multiple endo-crine neoplasia, type 2a" (MEN 2a). In the other, which they proposed becalled "multiple endocrine neoplasia, type 2b" (MEN 2b), the patientshad a characteristic appearance (thickened lips, mucosal ganglio-neuromatosis, and a marfanoid habitus) but no obvious parathyroid disease.

This paper describes the histologic characteristics of the parathyroid inpatients with MEN 2b and correlates it with the basal serum concentra-tions of calcium, phosphorus, and immunoreactive parathyroid hormone(iPTH) and with the iPTH response to calcium infusion.

Material and MethodsParathyroid tissue was available from 16 Mayo Clinic patients with MEN 2b ranging in

age from 2 years to 52 years (Table 1); 9 were female and 7 were male. Ten patients weremembers of three kindreds, in which the disorder had been transmitted in a pattern consis-

From the Departments of Surgical Pathology, Medicine (Endocrinology and Metabolism), and Pe-diatrics, Mayo Clinic and Mayo Foundation, Rochester, Minnesota, and the Department of Pathol-ogy, University of Arkansas College of Medicine, Little Rock, Arkansas (S.I.R.).

Accepted for publication December 27, 1979.Address reprint requests to J. A. Carney, MD, Mayo Clinic, Rochester, MN 55901.

0002-9440/80/0508-0387$01.00 387© American Association of Pathologists

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tent with autosomal-dominant inheritance. The parathyroid glands were removed surgi-cally for diagnostic purposes, accompanied a total thyroidectomy specimen, or were foundat autopsy. All 16 patients had C-cell disease of the thyroid gland (MTC or C-cell hyper-plasia or both), and 3 had adrenal medullary disease (pheochromocytoma or rrmdullary hy-perplasia or both). Plasma immunoreactive calcitonin (iCT) and serum iPT-I were mea-sured as previously described.3`5 The manner of presentation of the patients andpathologic features of the thyroid, adrenal, oral, and alimentary tract among the grouphave already been reported.9 No patient had symptoms or signs of hyperparathyroidism;but the oldest patient, a man of 52 years, had an asymptomatic renal calculus.

In addition to the Mayo Clinic pnaterial, we had the opportunity, through the generosityQf colleagues, to review the histologic studies of parathyroid tissue from 8 patients withMEN 2b not seen at the Mayo Clinic, none of whom had clinical evidence of hyper-parathyroidism (Table 2). A total of 34 parathyroid glands (21 from Mayo and 13 fromnon-Mayo patients, 33 of them intact and the other in the form of two fragments) wereavailable for histologic examination. All of the specimens were fixed in 10% buffered for-malin, and sectiqns of the paraffin-embedded tissue were stained with hematoxylin and eo-sin (H&E). The histologic features of the parathyroid glands were compared with those ofnormal glands from patients similar in age.

Results

Clinical Fipdings

The results of pertinent laboratory tests are presented in Tables 1(Mayo Clinic patients) and 2 (non-Mayo Clinic patients). All patients hadMTC except for one, who had C-cell hyperplasia, and nine had pheo-chromocytoma. Plasma iCT levels were high, either before or during stirn-ulation tests, in the patients for whom measurements were available. Inall patients the serum calcium concentrations were within two standarddeviations of the mean of the normal population, Although the meanserum levels of calcium for our patients were slightly higher than those ofthe normal population (9.4 versus 9.2 mg/dl), this difference was not sta-tistically significant. The serum concentration of phosphorus was normal,when measured, in all patients (children, such as Patients 2 and 3, Table 1,normally have a higher serum phosphorus level than adults). The iPTHlevels among 6 Mayo Clinic patients and their responses to calcium in-fusion, which have been reported previously,'0 were within the appropri-ate ranges for all patienits tested.

PatholQgic Findings

At cervical exploration, the parathyroid glands were considered macro-scopically normal by the surgeons. The histologic findings in the glandsfell into three categories: normal, mildly hyperplastic, and hyperplastic.

Normal Parathyroid Glands

Parathyroid glands from nine patients between the ages of 2 and 17years were considered to be within the normal histologic limits (Figure 1).


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Among these, the chief cells had a normal appearance. Varying amountsof stromal fat consistent with the age of the patients were present in allthe glands."-3 No gland showed appreciable perivascular fibrosis. Onepatient (Patient 5, Table 2) had replacement of the stromal adipose tissuewith loose fibrous tissue.

Mild Parathyroid Hyperplasia

Parathyroid glands from 12 patients ranging in age from 13 to 38 yearsexhibited histologic findings consistent with minimal to mild hyperplasia(Figures 2 and 3). The findings in the group consisted of varying degrees ofthe following alterations, compared with normal individuals of similarage: decreased stromal fat, more tightly packed small chief cells, and in-creased numbers of chief cells with large, clear, single cytoplasmic vacu-oles. There were also increased numbers of oxyphil cells (sometimes innodules), microcyst and follicle formation, nuclear enlargement, giant nu-clear forms, and multinucleated cells. Some of these glands appeared tohave increased vascularity. In two patients the hyperplasia was minimal.

Parathyroid Hyperplasia

One parathyroid gland from each of two patients (20 and 32 years old)and fragments of a parathyroid gland from a 52-year-old patient wereconsidered to be hyperplastic. The first patient had a parathyroid glandthat weighed 90 mg and was devoid of fat (Figure 4). Two other glandsfrom the same patient were considered not to be enlarged but were de-void of fat and had prominent perivascular fibrous tissue. In the secondpatient the gland was normal in size, but the chief cells were tightlypacked and frequently exhibited large, single cytoplasmic vacuoles (Figure5). There was slight perivascular fibrosis and only a minimal amount ofstromal fat. Oxyphil cells were present. In the last case the parathyroidfragments showed no fat or oxyphil cells; the chief cells were packed intonests, and there was focal perivascular fibrosis. Microcyst formation waspresent.

Discussion

Study of the histologic features of 34 parathyroid glands from 16 MayoClinic patients and 8 non-Mayo Clinic patients with MEN 2b suggests tous that there is an age-dependent histologic abnormality of the para-thyroid glands in the syndrome, contrary to the previously expressed opin-ion of one of us.'0 In order to confirm this impression conclusively, we willhave to repeat our study with the use of age-matched normal glands forcomparison with MEN 2b glands, coding all glands in such a way that the


status of the patients from whom they were obtained is unknown to theobserver.

In patients who had MEN 2b, the histologic characteristics of the para-thyroid were within normal limits through the middle of the second dec-ade. Subsequently, the normal increase in stromal fat was retarded. Fur-ther, there was an increase in the number of vacuolated chief cells and aslight acceleration in the appearance of the oxyphil cells. In patients pastthe mid-teen years, there was an increase in the number of chief cells withvacuolated cytoplasm similar to the chronically stimulated chief cells seenin secondary parathyroid hyperplasia.'4 Nuclear enlargement resemblingthat seen in adenomas and primary chief cell hyperplasia was also noted.'3These findings indicate a retardation of the normal involution of theglands that usually occurs in the postpubertal years after the period of ac-tive skeletal growth; the parathyroid glands maintained an inappropriatehistologic appearance, morphologically consistent with mild hyperplasia.

There is no consensus in the literature regarding the presence of para-thyroid disease in MEN 2b. Possible hyperplasia and adenoma havebeen reported in patients aged 15, 29, and 35 years, respectively,'='7whereas parathyroid gross or microscopic normality (in patients agedfrom 8 to 37 years) has also been described."820 Slightly elevated val-ues of serum iPTH in association with a serum calcium level of 10.0 mg/dlwere reported in a 45-year-old patient.2122 At age 47 this patient's cal-cium and phosphorus levels were 11.0 and 4.0 mg/dl, respectively, andthere was increased urinary excretion of calcium. Hyperparathyroidismwas suspected, but another measurement of the serum iPTH gave normalresults. Another reported patient had elevated serum calcium levels onseveral occasions and nephrolithiasis.' The serum levels of calcium in allof the Mayo Clinic patients were normal. Serum levels of iPTH were alsonormal, and there was a normal response of iPTH to calcium infusion (in-cluding our Patients 15 and 16, who had the most "severe" parathyroidhyperplasia).The paucity of evidence of serious abnormality of calcium metabolism

in MEN 2b seems to indicate that the parathyroid "hyperplasia" seen inassociation with MEN 2b is, for practical purposes, an anatomic deviationfrom normal that is only rarely associated with clinically or biochemicallyovert hyperparathyroidism. The histologic findings are, however, of theo-retical interest, and they engender speculation concerning their etiology.There are at least three possibilities: 1) the hyperplasia is a genetically de-termined defect and an inherent part of the MEN 2b syndrome, ie, mildprimary chief cell hyperplasia; 2) the hyperplasia is secondary, reflectingother aspects of the syndrome; 3) the hyperplasia is secondary and is ex-


acerbated by a genetic defect in parathyroid response ie, there is a combi-nation effect.

Before these explanations are considered, it should be emphasized thatthe diagnosis of parathyroid hyperplasia was not made merely because thestromal fat in the glands was considered to be decreased, although anevaluation of intracellular fat as a measure of cellular activity 24 or ultra-structure was not possible on the material available. There were, in addi-tion, cytologic changes in the cells consistent with hyperplasia (vacu-olization and nuclear enlargement). This is an important point, becausepatients with MEN 2b characteristically have decreased amounts of sub-cutaneous fat, and the possibility that the relative deficiency of fat in theparathyroid glands might be a manifestation of generalized involvementof adipose tissue in the syndrome should be considered. But the paren-chymal cytologic abnormalities just mentioned and the fact that stromalfat was present in the glands of young patients with the syndrome militateagainst a primary abnormality of fat being the explanation of the paucityof adipose tissue in the parathyroid glands of the older patients.

Concerning the other possible explanations of the hyperplasia, it shouldbe mentioned that the catecholamines produced by pheochromocytomasare largely the ,B-adrenergic agonists epinephrine and norepinephrine.These substances have been shown to stimulate the release of parathyroidhormone from isolated parathyroid chief cells.' Although constant, long-term stimulation of the parathyroid glands by epinephrine could conceiv-ably produce the "vacuolated" (chronically stimulated) chief cells seen inour patients, this substance has not been shown to produce parathyroidhyperplasia26; furthermore, the patients with the most severe "hyper-plasia" did not have pheochromocytoma.

Classic "secondary" hyperplasia of the parathyroid glands is generallybelieved to result from depression of the serum ionized calcium.'4 The lowambient serum calcium stimulates the chief cells in the G, (resting) phaseof the mitotic cycle to enter the SI (synthetic) phase and thus leads to hy-perplasia.27 In patients with MEN 2b, it could be argued that long-termelevation of circulating levels of calcitonin "antagonizes" the calcium-re-leasing effect of parathyroid hormone on bone and thereby causes a ten-dency toward depression of the serum calcium. This depression wouldthen result in mild secondary hyperplasia of the parathyroids. But thefinding of generally normal serum calcium and iPTH in the syndrome mil-itates against this theory.

In summary, available evidence provides few clues to the pathogenesisof the mild parathyroid hyperplasia we have found in MEN 2b. Hypocal-cemia, however mild, and hypercalcitoninemia seem to be unlikely cul-


prits, but the latter remains a possibility. Regardless of etiology, the para-thyroid disease in MEN 2b is rarely of clinical importance, and routineparathyroid surgery is not indicated. In the future it may be possible toobtain additional information concerning the pathophysiology of theparathyroid abnormality through long-term follow-up studies on the fewpatients who do not have hypercalcitoninemia after the "cure" of MTC.

References

1. Steiner AL, Goodman AD, Powers SR: Study of a kindred with pheochromocy-toma, medullary thyroid carcinoma, hyperparathyroidism and Cushing's disease:Multiple endocrine neoplasia, type 2. Medicine (Baltimore), 1968, 47:371-409

2. Chong GC, Beahrs OH, Sizemore GW, Woolner LB: Medullary carcinoma of thethyroid gland. Cancer 1975, 35:695-704

3. Sizemore GW, Go VLW, Kaplan EL, Sanzenbacher LU, Holtermuller KH, AmaudCD: Relations of calcitonin and gastrin in the Zollinger-Ellison syndrome and med-ullary carcinoma of the thyroid. N Engl J Med 1973, 288:641-644

4. Heath H III, Sizemore GW: Plasma calcitonin in normal man: Differences betweenmen and women. J Clin Invest 1977, 60:1135-1140

5. Arnaud CD, Tsao HS, Littledike T: Radioimmunoassay of human parathyroid hor-mone in serum. J Clin Invest 1971, 50:21-34

6. Carney JA, Sizemore GW, Hayles AB: C-cell disease of the thyroid gland in mul-tiple endocrine neoplasia, type 2b. Cancer 1979, 44:2173-2183

7. Carney JA, Sizemore GW, Sheps SG: Adrenal medullary disease in multiple endo-crine neoplasia, type 2: Pheochromocytoma and its precursors. Am J Clin Pathol1976, 66:279-290

8. Carney JA, Sizemore GW, Lovestedt SA: Mucosal ganglioneuromatosis, medullarythyroid carcinoma, and pheochromocytoma: Multiple endocrine neoplasia, type 2b.Oral Surg 1976, 41:739-752

9. Carney JA, Go VLW, Sizemore GW, Hayles AB: Alimentary-tract ganglio-neuromatosis: A major component of the syndrome of multiple endocrine neoplasia,type 2b. N Engl J Med 1976, 295:1287-1291

10. Heath H III, Sizemore GW, Carney JA: Preoperative diagnosis of occult para-thyroid hyperplasia by calcium infusion in patients with multiple endocrine neo-plasia, type 2a. J Clin Endocrinol Metab 1976, 43:428-435

11. Gilmour JR: The normal histology of the parathyroid glands. J Pathol Bacteriol1939, 48:187-222

12. Kaplan E: The parathyroid gland in infancy. Arch Pathol 1942, 34:1042-104913. Roth SI: Recent advances in parathyroid gland pathology. Am J Med 1971, 50:612-

62214. Roth SI, Marshall RB: Pathology and ultrastructure of the human parathyroid

glands in chronic renal failure. Arch Intern Med 1969, 124:397-40715. Voelkel EF, Tashjian AH Jr, Davidoff FF, Cohen RB, Perlia CP, Wurtman

RJ: Concentrations of calcitonin and catecholamines in pheochromocytomas, amucosal neuroma and medullary thyroid carcinoma. J Clin Endocrinol Metab 1973,37:297-307

16. Block MB, Roberts JP, Kadair RG, Seyfer AE, Hull SF, Nofeldt FD: Multiple endo-crine adenomatosis type Ilb: Diagnosis and treatment. JAMA 1975, 234:710-714

17. Bartlett RC, Myall RWT, Bean LR, Mandelstam P: A neuropolyendocrine syn-drome: Mucosal neuromas, pheochromocytoma, and medullary thyroid carcinoma.Oral Surg 1971, 31:206-220


18. Brown RS, Colle E, Tashjian AH Jr: The syndrome of multiple mucosal neuromasand medullary thyroid carcinoma in childhood: Importance of recognition of thephenotype for the early detection of malignancy. J Pediatr 1975, 86:77-83

19. Khairi MRA, Dexter RN, Burzynski NJ, Johnston CC Jr: Mucosal neuroma,pheochromocytoma and medullary thyroid carcinoma: Multiple endocrine neo-plasia type 3. Medicine (Baltimore) 1975, 54:89-112

20. Bartley PC, Lloyd HM, Aitken RE: Medullary carcinoma of the thyroid, multiplephaeochromocytomas, mucosal neuromas, marfanoid habitus and other abnormal-ities (Sipple's syndrome). Med J Aust 1976, 2:173-176

21. Desbois JC, Bienayme J, Bouveret JP, Cohen-Solal J, Herrault A: Les neoplasiesendocriniennes multiple de type II b (syndrome "aspect marfonaide, neuromatosemuqueuse multiple, cancer medullaire de la thyroide, pheochromocytome"): Etuded'une famille et revue de la litterature. Sem Hop Paris 1977, 53:1603-1613

22. Baillo F: Le syndrome des neuromes muqueux multiples: Un exemple de neuro-christopathie complexe. Thesis, Universite Paul Sabatier, Toulouse, France, 1977

23. Ljungberg 0: On medullary carcinoma of the thyroid. Acta Pathol Microbiol Scand[A] 1972, Suppl 231:1-57

24. Roth SI, Gallagher MJ: The rapid identification of "normal" parathyroid glands bythe presence of intracellular fat. Am J Pathol 1976, 84:521-528

25. Brown EM, Hurwitz S, Aurbach GD: Beta-adrenergic stimulation of cyclic AMPcontent and parathyroid hormone release from isolated bovine parathyroid cells. En-docrinology 1977, 100:1696-1702

26. Miller SS, Sizemore GW, Sheps SG, Tyce GM: Parathyroid function in patientswith pheochromocytoma. Ann Intern Med 1975, 82:372-375

27. Roth SI, Au WYW, Kunin AS, Krane SM, Raisz LG: Effect of dietary deficiency invitamin D, calcium, and phosphorus on the ultrastructure of the rat parathyrQidgland. Am J Pathol 1968, 53:631-650

AcknowledgmentsThe authors wish to thank Drs. J. L. Bonenfant, J. Dainauskas, E. Olen, R. A. Perez, J. Rosai, J. A.

Seab, Jr., and A. J. Watson, who supplied pathologic material used in this study.


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5~~~~~~~~~~~~~~~~&Figure 4-Absence of stromal fat in a parathyroid gland weighing 90 mg,from a 20-year-old woman, indicative of hyperplasia. Figure 5Hyper-plasia shown by the tightly packed solid parenchyma in the parathyroidgland of a 32-year-old man. (H&E, x 100) Inset-Higher power magnifi-cation of the cells in Figure 5, showing large cytoplasmic vacuoles. (H&E,x400)

the parathyroid glands in multiple endocrine neoplasia type 2b

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