Acromegaly caused by growth hormone-releasing hormone-producing tumors: long-term observational studies in three patients

Acromegaly caused by ectopic extracranial growth hormone-releasing hormone (GHRH) secretion is a very rare disorder occurring probably in less than 1 % of the acromegalic patients [1]. The majority of the GHRH-secreting tumors are bronchial carcinoids. Other GHRH-secreting tumors in decreasing order of occurrence are pancreatic adenomas, gastro-intestinal tumors, thymic tumors, and tumors associated with the MEN-I syndrome [2].

Here we report our clinical experience in three patients with the ectopic GHRH-syndrome derived from a population of over 200 acromegalic patients, diagnosed and treated at the Leiden University Medical Center from 1976 till 2002. Long-term follow-up studies in these patients and results of medical therapy with somatostatin analogs are scarce. The purpose of this report is to expand our knowledge of this rare clinical entity. In addition, we report detailed results of diurnal GH secretion, before and after removal of the GHRH-producing source in order to investigate whether pulsatile and basal GH secretion due to GHRH overproduction differs from that of a primary pituitary somatotropinoma.

Basal concentrations of hormones, including prolactin, free thyroxin, triiodothyronine, cortisol, testosterone, estradiol, progesterone, IGF-I, and IGFBP3 were measured. In addition the following tests were performed: Oral glucose loading test (75 g), TRH test (200 μg i.v. ), and a GHRH test (50 μg i.v. ) and the following hormones were measured: glucose tolerance test: GH, insulin and glucose at 0, 30, 60, 90 and 120 min, TRH test: TSH, prolactin and GH at −15, 0, 15, 20, 30 45, 60, 90 and 120 min; GHRH test: GH and prolactin at 0, 20, 30, 45, 60, and 90 min. For the 24-h GH secretion profile the patients were hospitalized, and an indwelling i.v. cannula was inserted in a forearm vein, and blood samples were withdrawn at 10-min intervals. The patients were free to move around, but not to sleep during daytime. Meals were served at 0800, 1230 and 1730 h. Lights were turned off between 2200 and 2400 h.

Case 1. A 50-year-old male was referred in 1982 because of recurrent kidney stones, hypercalciuria (24 h urinary calcium excretion between 14.5 mmol and 16.3 mmol, normal upper value 6 mmol/24 h) and hypercalcaemia (serum Ca between 2.86 mmol/l and 2.95 mmol/l, normal values between 2.25 mmol/l and 2.60 mmol/l). The referring internist suspected the patient of having mild acromegaly, because of the coarse facial features. The diagnosis primary hyperparathyroidism was confirmed and the patient underwent parathyroid surgery, and two large adenomas were removed, after which the patient became normocalcaemic until now. The patient had noted increase in size of his feet and hands since several years, but otherwise he had no complaints. Glucose loading decreased GH from 12 mU/l to below 0.5 mU/l (normal value during glucose suppression is below 2.5 mU/l with RIA). Intravenous administration of 200 μg TRH, however, increased GH from 3.5 mU/l to 58.0 mU/l and PRL increased from 7.0 μg/l to 13 μg/l. CT scanning of the pituitary gland with the first generation CT-scanner (in 1983) did not show abnormalities, and CT scanning of the thorax and abdomen also failed to show the presence of a tumor. Because of progressive complaints of fatigue after cure for hyperparathyroidism and strong clinical suspicion of acromegaly, the patient underwent transsphenoidal pituitary exploration. At surgery a small suspect lesion was removed with part of the surrounding pituitary gland tissue. Histology of the lesion was compatible with somatotrope hyperplasia. After the patient had recovered from surgery, CT, MRI and arteriographic studies were repeated, and serum samples were sent to St. Bartholomew’s Hospital, London, UK (Dr L.H. Rees) for GHRH measurement. The abdominal CT-scan showed a 4 cm mass in the middle section of the pancreas (Fig. 1) and the mass was also visible with selective arteriography of the superior mesenterial artery (Fig. 1). The fasting GHRH concentration amounted to 3,810 pg/ml (normal range 10–60 pg/ml). GHRH concentration in the arterial supply to the tumor was 12,470 pg/ml, and in the venous tumor outflow 31,120 pg/ml, while in the systemic venous system the concentration was 8,900 pg/ml. After removal of the pancreatic tumor, peripheral GHRH concentration decreased to normal values of 16–33 pg/ml. In retrospect, the first abdominal CT-scan, 2 years before, already showed the pancreatic tumor with a similar size.

The patient was the index case of a large kindred affected by MEN-I syndrome. Later, a gene mutation was revealed in exon 2 of chromosome 11q13. During long-term follow-up GH and IGF-I concentrations remained normal.

Six years later, in 1988, the patient developed diabetes mellitus, initially treated with oral hypoglycemic drugs and with insulin from 1992 onwards. The patient also had mild bilateral nodular adrenal hyperplasia since 1988, with no evidence of growth during the last recent 10 years. No excess of adrenal (cortex and medulla) hormones or precursors was demonstrable during follow-up. During the last 3 years the plasma level of pancreatic polypeptide (PP) increased to 350 nmol/l (normal < 100 nmol/l). Repeat CT and MRI scanning of the upper abdomen failed to reveal the presence of a pancreatic tumor thus far.

Random serum GH during follow-up ranged from 0.16 mU/l to 1.81 mU/l and IGF-I ranged from 12 nmol/l to 17 nmol/l from 1994 till now (see Fig. 2). All these values are perfectly normal for his age and gender. The last serum GHRH measurement in 2006 was normal with 32 pg/ml.

Case 2. A 27-year-old acromegalic female patient was referred in 1993 to our center for octreotide treatment. She had a 5-year history of hyperhydrosis, fatigue, paraesthesias, and acral enlargement. After delivery of a healthy daughter in 1992 she had persisting amenorrhea and galactorrhea. Physical examination revealed mild, although characteristic features of acromegaly. Serum GH concentration was elevated at 99 mU/l and decreased insufficiently to 55 mU/l following oral glucose administration. IGF-I concentration amounted to 86 nmol/l (normal upper level for her age 32 nmol/l) Thyroid and adrenal functions were normal, but prolactin concentration was elevated to 20 μg/l (normal upper limit for females 12 μg/l). Other investigations performed (TRH test, GHRH test, and the i.v. octreotide test) are summarized in Fig. 3. TRH bolus injection (200 μg iv) caused a ∼8-fold increase of GH and a 3.5-fold increase of PRL. Intravenous injection of 50 μg GHRH (1-40) caused a decrease of GH while PRL concentrations remained unchanged. Octreotide (50 μg i.v.) caused a 98% inhibition of serum GH but no effect on PRL. MRI scanning of the pituitary gland showed global enlargement without signs of an adenoma (Fig. 4). Further investigations revealed a large tumor in the right lower lobe of the lung (Fig. 5). The tumor and the pituitary gland were positive on ¹¹¹In-labeled-octreotide scintigraphy (Fig. 6). The plasma GHRH concentration was increased 50-fold by 2,519 pg/ml (normal values <50 pg/ml).

Under the diagnosis of ectopic GHRH-producing lung tumor (carcinoid) the patient underwent thoracotomy and the tumor was resected completely. The plasma GHRH disappearance profile after removal of the tumor is shown in Fig. 7, but the GHRH concentration did not normalize. GHRH concentrations in simultaneously withdrawn blood samples from the arterial supply to the tumor, venous tumor outflow and the systemic venous system were 1,890, 2,180, and 1,680 pg/ml, respectively.

Two weeks after surgery, endocrine investigations revealed a persisting paradoxical increase (9-fold) of GH to TRH, insufficient GH suppression after oral glucose loading (52–16 mU/l) and a GH increase after GHRH injection. Octreotide caused a 98% decrease of GH from 41 mU/l to 0.9 mU/l (see Fig. 3). Treatment with octreotide was started in 1994, about 8 months after surgery, because of persisting elevated GHRH concentration (between 360 pg/ml and 488 pg/ml), increased GH( 31–42 mU/l), insufficient suppression by glucose loading (minimum GH concentration 9.13 mU/l), an increased IGF-I concentration ( 40–43 nmol/l), and lesions in the liver on repeat CT scans, suspect for metastases (one lesion in segments 2 and 8, and two lesions in segment 7).

Case 3. A 27-year-old male was referred in 1997 to our center. He had a 9-year history of hyperhydrosis, acral enlargement and headaches. Examination revealed moderately advanced features of acromegaly. The circulating GH concentration was elevated at 110 mU/l and decreased insufficiently to 52 mU/l following glucose administration, and IGF-I was elevated to 63 nmol/l (normal upper level at this age 32 nmol/l). Thyroid and adrenal functions were normal, but prolactin concentration was elevated to 21 μg/l (normal upper limit for males 6 μg/l). Other investigations performed (TRH test and the i.v. octreotide test) are summarized in Fig. 3. TRH bolus injection (200 μg i.v.) caused a ∼8-fold increase of GH and a 2-fold increase of PRL. Octreotide (50 μg i.v) caused a 94% inhibition of GH (Fig. 3). MRI scanning of the pituitary gland showed a macroadenoma II ^AE (Hardy classification, modified by Wilson [12, 13] see Fig. 4). He was treated for 6 months with sc octreotide (100 μg tid). The size of the adenoma decreased slightly, but because of the moderate clinical response to medical treatment and failure of normalization of GH and IGF-I, pituitary surgery was advised. One day before surgery a chest X-ray was taken, showing a large parahilar lesion (Fig. 5). CT scanning of this lesion was classified by the consultant pulmonologist and radiologist as a bronchial cyst and apparently unrelated to acromegaly. During pituitary surgery the adenoma was removed completely, but the neurosurgeon remarked that the consistency of the adenoma was firmer than normal. Since we suspected that the lung tumor was potentially a GHRH-producing source, postoperative investigations were focused on this possibility. After surgery, MRI scanning of the pituitary region did not show residual tumor, GH concentrations decreased considerably and PRL concentrations became normal. GH dynamic tests did not completely normalize: GH increased after TRH injection from 4.63 mU/l to 22.1 mU/l and after glucose loading GH decreased from 4.33 mU/l to 2.56 mU/l (normal value below 1 mU/l). During an i.v. octreotide test GH decreased from 6.21 mU/l to 0.85 mU/l, but treatment with this drug was not reinstituted. On ¹¹¹In-labelled-octreotide scanning the tumor was positive (see Fig. 6).

Under the diagnosis of ectopic GHRH-producing lung tumor (carcinoid) the patient underwent thoracotomy and the tumor was removed completely. GHRH concentrations in the arterial supply to the tumor were 48,290 pg/ml, in the venous outflow 94,000 pg/ml and in the systemic venous system 49,000 pg/ml. After removal of the tumor GHRH concentrations remained slightly elevated, as shown in Fig. 7.

In this study we described in detail the clinical and biochemical characteristics of three patients with ectopic extracranial GHRH secretion diagnosed in a series of about 200 acromegalics investigated and treated in our center during the last 25 years. The incidence in the present series agrees with that mentioned in literature [1, 16]. Faglia summarized the clinical findings of 39 reported acromegalic patients with proven ectopic GHRH secretion [17]. Subsequently, van den Bruel and colleagues [18] mentioned 52 reported patients in 1999, including their own patient and since then 14 other patients have been reported, bringing the total number reported to 66 patients [19‐32]. From a conservative estimation of the total number of newly diagnosed acromegalic patients in Europe, Japan and the USA, it is evident that most patients with ectopic GHRH syndrome are either not reported or remain undiagnosed.

The criteria for demonstration of ectopic extracranial GHRH-induced acromegaly are summarized by Losa and von Werder [2], and include the presence of high circulating concentration GHRH by specific radioimmunoassays, the presence of GHRH in the tumor, the presence of mRNA for GHRH by in situ hybridization and/or a significant arterio-venous gradient across the ectopic source. The second requirement to be fulfilled is the reversibility of acromegaly after complete removal of the ectopic-hormone producing tumor. All our patients met at least two criteria, although the tumors were not investigated for the presence of GHRH.

The clinical symptomatology in ectopic GHRH-induced acromegaly is not different from that of the primary pituitary adenomatous form. However, symptoms due to the underlying neoplasm or cosecretion of other substances by the tumor might suggest the ectopic origin of acromegaly [33]. Specific dynamical tests for GH excess do not allow classification with certainty in either category, although most patients with ectopic GHRH syndrome exhibit a paradoxical increase of GH after TRH and glucose (i.e. >50%) and a blunted GH rise (<100%) after exogenous GHRH injection [33]. In addition, most patients also exhibit a moderate increase in serum prolactin concentration, which regresses after removal of the ectopic GHRH source, supporting the notion that GHRH is directly responsible for the hyperprolactinemia, a finding also present in hGHRH-transgenic mice [34]. The patients reported here all exhibited GH increase after TRH, and two had mild hyperprolactinemia. After surgery, hyperprolactinemia normalized, but GH still increased after TRH administration, suggesting that GHRH was still being produced by tumor remnants or metastases in two patients (nos. 2 and 3).

The most frequent source of ectopic GHRH is the bronchial carcinoid, followed by pancreatic islet tumors [17], as we also found in the present evaluation of our patient series. The pancreatic tumor in the first patient was found by CT-scanning and MRI. The large bronchial carcinoids were easily seen by chest X-ray examination, and showed uptake of radio-labeled octreotide, thus demonstrating in vivo the presence of somatostatin receptors. Although positive somatostatin receptor-scintigraphy is usually found in carcinoids in general, its demonstration in ectopic GHRH tumors is limited. Nevertheless, this examination could be particularly useful in the diagnostic phase of patients with suspected, but not yet proven, ectopic GHRH secretion.

Histological investigation of surgically removed pituitary tissue revealed pituitary hyperplasia in most cases (i.e. with an intact reticulin fiber network), but in other patients adenomatous transformation can be found [35]. Indeed, the histological findings in hGHRH transgenic mice resemble those in the human: in young animals diffuse hyperplasia was found, while those of older mice showed adenomas [34, 36]. The pathological changes in the pituitary gland are the result of GHRH per se and not of GH, since hyperplasia and tumor formation still occur in the absence of GH signaling [37]. A hypothalamic GHRH-producing tumor (gangliocytoma) is generally associated with a pituitary adenoma rather than with pituitary hyperplasia and is attributed to a much higher (assumed) local (pituitary) concentration of GHRH or the presence of other growth stimulating factors [38]. In addition, the combination of an intrasellar GHRH-containing gangliocytoma and a somatotropinoma has been described in rare patients [39, 40]. In two of our patients pituitary histology was available: one patient (no. 1) showed hyperplasia in the absence of an enlarged gland, while histology in the other patient (no. 3) showed a mixture of hyperplasia and adenomatous transformation.

Neuroimaging studies of the pituitary gland are variable: in about half of the patients no tumor or a slight enlargement of the sella is detected, while in other patients intrasellar adenomas or macroadenomas with suprasellar extension are found [18]. The CT-scan of patient 1 was normal and MRI scanning in patient 2 showed diffuse enlargement of the pituitary gland without a clear adenoma and with diffuse uptake of gadolinium DTPA. In patient 3 asymmetric enlargement was present, suggestive of a macroadenoma, but uptake of gadolinium DTPA throughout the whole pituitary gland was diffuse, illustrating the variability of imaging results. Although the pituitary MRI studies in the ectopic GHRH syndrome are non-specific, in the absence of a clear adenoma, ectopic GHRH secretion should be considered and appropriate investigations installed to prevent unnecessary pituitary surgery. On the other hand, primary medical treatment for acromegaly in these patients might obscure the real cause.

Carcinoids, especially of the lung and gastrointestinal tract constitute about two-thirds of all cases reported so far, followed by pancreatic islet cell tumors [17, 33]. Metastases of carcinoid tumors were present in about 30%, a frequency similar to lung carcinoids in general [35]. Two of our patients had a large primary lung carcinoid, but had no histological proven metastases. Because serum GHRH concentration did not normalize after removal of the GHRH source we assumed (liver) metastases.

Immunochemistry of the GHRH-secreting tumors has regularly demonstrated cosecretion of other hormones, including gastrin, gastrin-releasing peptide, calcitonin, pancreatic polypeptide, VIP, glucagon, insulin, and somatostatin, pointing to the multihormonal nature of these tumors. Particularly, cosecretion of somatostatin may modify the clinical picture and severity [31‐44].

Only few patients with a GHRH-producing pancreatic islet cell tumor and with MEN I syndrome have been described [41, 43, 44]. In agreement with our patient 1, they had multiple tumors; however, the pancreatic tumors in our patient showed an identical immunohistochemical profile in contrast with the other reported patients. The tumor stained positively for somatostatin, which might explain the only moderately increased GH concentration and possibly also the normal GH response to glucose loading, as alluded to above. In the follow-up of more than 20 years, no recurrence of acromegaly occurred, but the (modest) increase of pancreatic polypeptide could point to the development of a new pancreatic adenoma.

GH secretory characteristics of two patients were investigated before removal of the GHRH source. We established that pulsatile and non-pulsatile (basal) secretion, pulse frequency and secretory regularity (ApEn) were comparable to untreated acromegalic patients with primary pituitary adenomas [8, 45]. Because of the highly significant copulsatility of GHRH and GH in two other patients reported in literature, it is reasonable to postulate that pulsatile GH secretion in these patients was generated via episodic GHRH secretion of the primary tumor, while in patients with a pituitary GH-secreting adenoma pulsatile secretion is probably a tumorous feature [8].

Approximate entropy calculations of serum GHRH profiles disclosed high values, suggesting highly irregular secretion, a feature common with many other hormone-secreting tumors [7‐9]. It is reasonable to assume that the irregular secretion of GH in the four patients who were investigated till now was mainly the result of the irregular GHRH-input signal, and analogous to the irregular cortisol secretion driven by ACTH in pituitary-dependent Cushing’s syndrome [7, 46]. Nevertheless, part of the irregularity of GH secretion might also be due to increased GHRH per se, since GHRH infusion in healthy subjects augments irregular GH secretion [47]. After surgery and on effective octreotide therapy aimed at normalizing IGF-I, GH secretion became almost normal. GH secretion remained however irregular (increased ApEn), notwithstanding the increased feedback signal of octreotide, and the diminished forward input signal of GHRH by octreotide [48, 49]. Similarly, octreotide treatment in (classical) acromegaly represses secretory-burst mass and non-pulsatile secretion but does not restore event frequency or orderly GH secretion [50]. Collectively, these results suggest that even a modestly increased GHRH concentration can maintain irregular GH secretion in ectopic acromegaly.