Complex rhythmicity and age dependence of growth hormone secretion are preserved in patients with acromegaly: further evidence for a present hypothalamic control of pituitary somatotropinomas

"Micromegaly": Acromegaly with apparently normal GH, an entity on its own?

A small proportion of the patients with acromegaly present with apparently normal basal GH levels and suppressible GH levels despite increased IGF-1 levels, a pattern called micromegaly by some authors. Whether this pattern represents a distinct entity or is just an expression of acromegaly in its early stages is still a matter of debate. Nevertheless, these patients have some peculiar characteristics such as being more likely older and male, mostly harbour microadenomas or small macroadenomas, and have lower IGF-1 and postglucose GH levels. Even though, the frequency and severity of clinical signs and comorbidities are similar to those of patients with classic acromegaly. In conclusion, micromegaly seems to be a distinct clinical entity with a different biological behavior characterized by a low GH output.

Paradoxical GH increase after oral glucose load in subjects with and without acromegaly

OBJECTIVE

A paradoxical GH rise after the glucose load (GH-Par) is described in about one-third of acromegalic patients. Here, we evaluated the GH profile in subjects with and without acromegaly aiming to refine the definition of GH-Par.

DESIGN

Observational case-control study.

METHODS

Our cohort consisted of 60 acromegalic patients, and two groups of subjects presenting suppressed GH (< 0.4 µg/L) and high (non-acro↑IGF-1, n = 116) or normal IGF-1 levels (non-acro, n = 55). The distribution of GH peaks ≥ 120% from baseline, insulin, and glucose levels were evaluated over a 180-min time interval after glucose intake.

RESULTS

A similar proportion of subjects in all three groups shows a GH ratio of ≥ 120% starting from 120 min. Re-considering the definition of paradoxical increase of GH within 90 min, we observed that the prevalence of GH peaks ≥ 120% was higher in acromegaly than in non-acro↑IGF-1 and non-acro (respectively 42%, 16%, and 7%, both p < 0.001). In patients without GH-Par, a late GH rebound was observed in the second part of the curve. Higher glucose peak (p = 0.038), slower decline after load, 20% higher glucose exposure (p = 0.015), and a higher prevalence of diabetes (p = 0.003) characterized acromegalic patients with GH-Par (with respect to those without).

CONCLUSIONS

GH-Par response may be defined as a 20% increase in the first 90 min after glucose challenge. GH-Par, common in acromegaly and associated with an increased prevalence of glucose metabolism abnormalities, is found also in a subset of non-acromegalic subjects with high IGF-1 levels, suggesting its possible involvement in the early phase of the disease.

Systemic comorbidities of acromegaly in real-life experience: which difference among young and elderly patients?

INTRODUCTION

Acromegaly is a rare but potentially life-threatening disease, if not promptly managed, for the systemic complications due to the GH/IGF-I hypersecretion. According to the increased population life span, the number of older acromegaly patients is growing. We aim to investigate clinical features of elderly acromegaly (elderly-ACRO) and to identify the risk factors for the occurrence of comorbidities in elderly-ACRO.

MATERIALS AND METHODS

A retrospective and multi-center study was performed on acromegaly patients. Acromegaly comorbidities were compared among elderly-ACRO (>65 years), young acromegaly patients (young-ACRO if ≤65 years) and a control group of age and gender-matched subjects.

RESULT

Fifty of the 189 enrolled patients were elderly-ACRO (26.5%). Cardiovascular, metabolic, neurological/psychiatric and joint/articular disorders, nodular thyroid disease, sleep apnoea syndrome and skeletal fragility occurred more frequently in elderly-ACRO as compared to controls. Cardiovascular and metabolic disorders, nodular thyroid disease occurred significantly more frequently in elderly-ACRO as compared to young-ACRO and controls. On the other hand, neurological/psychiatric, joint/articular disorders and bone fragility occur with a similar frequency among elderly and young-ACRO. We found that elderly-ACRO had an increased risk for the occurrence of systemic arterial hypertension (p < 0.001, OR: 5.4 95%IC:2.6-10.9), left ventricular hypertrophy (p = 0.01, OR: 3 95%IC: 1.5-5.8) and metabolic disorders (p = 0.006, OR: 4.1 95%IC: 2-8.3).

CONCLUSION

Our results may suggest that some acromegaly comorbidities may be predominantly due to acromegaly "per-se" rather than to aging. On the contrary, cardiovascular and metabolic disorders seem to be due to aging as well.

Insulin-like growth factor-1 (IGF-1) as predictor of cardiovascular mortality in heart failure patients: data from the T.O.S.CA. registry

INTRODUCTION

Data from the "Trattamento Ormonale nello Scompenso CArdiaco" (T.O.S.CA) registry showed that heart failure (HF) represents a complex clinical syndrome with different hormonal alterations. Renal failure represents a frequent complication in HF. We evaluated the relationship between renal function and insuline-like growth factor-1 (IGF-1) deficiency and its impact on cardiovascular mortality (CVM) in patients enrolled in the T.O.S.CA. registry.

METHODS

At the enrolment, all subjects underwent chemistry examinations, including circulating hormones and cardiovascular functional tests. COX regression analysis was used to evaluate factors related to CVM during the follow-up period in all populations, in high-risk patients and in the young-adult population. Also, we evaluate the effects of renal function on the CVM.

RESULTS

337 patients (41 deceased) were analyzed. CVM was related to severe renal dysfunction (HR stages IV-V = 4.86), high-risk conditions (HR 2.25), serum IGF-1 (HR 0.42), and HF etiology (HR 5.85 and HR 1.63 for valvular and ischemic etiology, respectively). In high-risk patients, CVM was related to IGF-1 levels, severe renal dysfunction and valvular etiology, whereas in young patients CMV was related to the high-risk pattern and serum IGF-1 levels.

CONCLUSIONS

Our study showed the clinical and prognostic utility of the IGF-1 assay in patients with HF.

The biochemical diagnosis of acromegaly: revising the role of measurement of IGF-I and GH after glucose load in 5 questions

INTRODUCTION

Acromegaly is a rare disorder characterized by the excessive secretion of growth hormone (GH), mostly caused by pituitary adenomas. While in full-blown cases the diagnosis is easy to establish, milder cases are more challenging. Additionally, establishing whether full cure after surgery is reached may be difficult.

AREAS COVERED

In this article, we will review the challenges posed by the variability in measurements of GH and its main effector insulin-like growth factor I (IGF-I) due to both biological changes, co-morbidities, and assays variability.

EXPERT OPINION

Interpretation of GH and IGF-I assays is important in establishing an early diagnosis of acromegaly, in avoiding misdiagnosis, and in establishing if cure is achieved by surgery. Physicians should be familiar with the variables that affect measurements of these 2 hormones, and with the performance of the assays available in their practice.

Soluble Alpha Klotho in Acromegaly: Comparison With Traditional Markers of Disease Activity

CONTEXT

Soluble alpha klotho (sαKL) has been linked to growth hormone (GH) action, but systematic evaluation and comparisons with traditional biomarkers in acromegaly are lacking.

OBJECTIVE

To evaluate the potential of sαKL to aid classification of disease activity.

METHODS

This retrospective study at 2 academic centers included acromegaly patients before surgery (A, n = 29); after surgery (controlled, discordant, or uncontrolled) without (B1, B2, B3, n = 28, 11, 8); or with somatostatin analogue treatment (C1, C2, C3, n = 17, 11, 5); nonfunctioning pituitary adenomas (n = 20); and healthy controls (n = 31). sαKL was measured by immunoassay and compared with traditional biomarkers (random and nadir GH, insulin-like growth factor I [IGF-I], IGF binding protein 3). Associations with disease activity were assessed.

RESULTS

sαKL was correlated to traditional biomarkers, particularly IGF-I (rs=0.80, P <0.0001). High concentrations before treatment (A, median, interquartile range: 4.04 × upper limit of normal [2.26-8.08]) dropped to normal after treatment in controlled and in most discordant patients. A cutoff of 1548 pg/mL for sαKL discriminated controlled (B1, C1) and uncontrolled (B3, C3) patients with 97.8% (88.4%-99.9%) sensitivity and 100% (77.1%-100%) specificity. sαKL was below the cutoff in 84% of the discordant subjects. In the remaining 16%, elevated sαKL and IGF-I persisted, despite normal random GH. Sex, age, body mass index, and markers of bone and calcium metabolism did not significantly affect sαKL concentrations.

CONCLUSION

Our data support sαKL as a biomarker to assess disease activity in acromegaly. sαKL exhibits close association with GH secretory status, large dynamic range, and robustness toward biological confounders. Its measurement could be helpful particularly when GH and IGF-I provide discrepant information.

Discordant GH and IGF-1 Results in Treated Acromegaly: Impact of GH Cutoffs and Mean Values Assessment

CONTEXT

Discordant growth hormone (GH) and insulin-like growth factor-1 (IGF-1) values are frequent in acromegaly.

OBJECTIVE

To evaluate the impact of different GH cutoffs on discordance rate. To investigate whether the mean of consecutive GH measurements impacts discordance rate when matched to the last available IGF-1 value.

DESIGN

Retrospective study.

SETTING

Referral center for pituitary diseases.

PATIENTS

Ninety acromegaly patients with at least 3 consecutive evaluations for GH and IGF-1 using the same assay in the same laboratory (median follow-up 13 years).

INTERVENTIONS

Multimodal treatment of acromegaly.

MAIN OUTCOME MEASURES

Single fasting GH (GHf) and IGF-1 (IGF-1f). Mean of 3 GH measurements (GHm), collected during consecutive routine patients' evaluations.

RESULTS

At last evaluation GHf values were 1.99 ± 2.79 µg/L and age-adjusted IGF-1f was 0.86 ± 0.44 × upper limit of normality (mean ± SD). The discordance rate using GHf was 52.2% (cutoff 1 µg/L) and 35.6% (cutoff 2.5 µg/L) (P = 0.025). "High GH" discordance was more common for GHf <1.0 µg/L, while "high IGF-1" was predominant for GHf <2.5 µg/L (P < 0.0001). Using GHm mitigated the impact of GH cutoffs on discordance (GHm <1.0 µg/L: 43.3%; GHm <2.5 µg/L: 38.9%; P = 0.265). At receiver-operator characteristic curve (ROC) analysis, both GHf and GHm were poor predictors of IGF-1f normalization (area under the curve [AUC] = 0.611 and AUC = 0.645, respectively). The prevalence of disease-related comorbidities did not significantly differ between controlled, discordant, and active disease patients.

DISCUSSION

GH/IGF-1 discordance strongly depends on GH cutoffs. The use of GHm lessen the impact of GH cutoffs. Measurement of fasting GH levels (both GHf and GHm) is a poor predictor of IGF-1f normalization in our cohort.

Clinical presentation and management of acromegaly in elderly patients

BACKGROUND AND AIM

Acromegaly is a rare disease with a peak of incidence in early adulthood. However, enhanced awareness of this disease, combined with wide availability of magnetic resonance imaging (MRI), has increased the diagnosis of forms with mild presentation, especially in elderly patients. Moreover, due to increased life expectancy and proactive individualized treatment, patients with early-onset acromegaly are today aging. The aim of our study was to describe our cohort of elderly patients with acromegaly.

MATERIALS AND METHODS

This is a cross-sectional retrospective study of 96 outpatients. Clinical, endocrine, treatment, and follow-up data were collected using the electronic database of the University Hospital of Padova, Italy.

RESULTS

We diagnosed acromegaly in 13 patients, aged ≥65 years, presenting with relatively small adenomas and low IGF-1 secretion. Among them, 11 patients were initially treated with medical therapy and half normalized hormonal levels after 6 months without undergoing neurosurgery (TNS). Remission was achieved after TNS in three out of four patients (primary TNS in two); ten patients presented controlled acromegaly at the last visit. Acromegaly-related comorbidities (colon polyps, thyroid cancer, adrenal incidentaloma, hypertension, and bone disease) were more prevalent in patients who had an early diagnosis (31 patients, characterized by a longer follow-up of 24 years) than in those diagnosed aged ≥65 years (5 years of follow-up).

CONCLUSIONS

Elderly acromegalic patients are not uncommon. Primary medical therapy is a reasonable option and is effectively used, while the rate of surgical success is not reduced. A careful cost-benefit balance is suggested. Disease-specific comorbidities are more prevalent in acromegalic patients with a longer follow-up rather than in those diagnosed aged ≥65 years.

Multicenter, Observational Study of Lanreotide Autogel for the Treatment of Patients with Acromegaly in Routine Clinical Practice in Germany, Austria and Switzerland

BACKGROUND

Evidence from controlled trials has shown that lanreotide autogel is effective in achieving biochemical and symptom control in patients with acromegaly. However, it is important to better understand the real-world patient population receiving lanreotide autogel treatment.

METHODS

In this non-interventional study the long-term treatment response to lanreotide autogel in adult patients with acromegaly from office-based centers or clinics in Germany, Austria and Switzerland was studied. Assessments included growth hormone and insulin-like growth factor-I levels, symptoms, quality of life, lanreotide plasma levels and tumor somatostatin receptor subtype expression. The primary endpoint was achievement of full biochemical control, defined as growth hormone ≤2.5 µg/L and insulin-like growth factor I normalization at month 12.

RESULTS

76 patients were enrolled from 21 sites. 7/51 (13.7%) patients of the efficacy population had full biochemical control at baseline, 15/33 (45.5%) at month 12 and 10/26 (38.5%) at month 24 of treatment. At 12 months of treatment higher rates of biochemical control were observed in the following subgroups: older patients (>53 years [median]), females, treatment-naïve patients, and patients with a time since diagnosis of longer than 1.4 years (median). No clinically relevant differences in acromegaly symptoms or quality of life scores were observed. Median fasting blood glucose and glycated hemoglobin levels remained unchanged throughout the study. No new safety signals were observed. Overall tolerability of treatment with lanreotide autogel was judged by 80.8% of the enrolled patients at month 12 as 'very good' or 'good'.

CONCLUSION

Treatment with lanreotide autogel in a real-world setting showed long-term effectiveness and good tolerability in patients with acromegaly.

Random Gh and Igf-I levels after transsphenoidal surgery for acromegaly: relation with long-term remission

PURPOSE

To evaluate the role of IGF-I and random GH measurements 3 months after transsphenoidal surgery (TSS) in predicting long-term remission in acromegaly patients.

METHODS

Retrospective analysis of 54 acromegaly patients who underwent TSS with the same neurosurgery team. Random GH and IGF-I values evaluated 3 months after TSS were related to long-term outcomes. The initiation of adjuvant therapy at any time defined surgical failure.

RESULTS

At 3 months, 14 (25.9%) patients had controlled disease (CD; normal IGF-I and GH < 1.0 µg/L), 25 (46.3%) had uncontrolled disease (UD; high IGF-I and GH), and 15 (27.8%) had biochemical discrepancies (BD): 12 BDI (normal IGF-I + GH ≥ 1.0 μg/L) and 3 BDII (high IGF-I + GH < 1.0 μg/L). All patients of the CD group, 2 of the UD, 11 of the BDI, and 2 of the BDII, progressed with long-term remission and had IGF-I ≤ 1.25-fold the Upper Limit of Normal (ULN), in contrast with all cases of surgical failure where IGF-I was ≥1.3-fold ULN. Only one patient with normal IGF-I had recurrence, resulting in 100% sensitivity and 96% specificity of post-surgical IGF-I ≤ 1.25-fold ULN to predict long-term remission, observed in 54% of our cohort. Post-surgical random GH ≥ 1.7 µg/L was the best cutoff to identify surgical failure, but its accuracy to predict long-term outcomes was limited.

CONCLUSIONS

IGF-I levels ≤ 1.25-fold ULN 3 months after TSS was the best guide for long-term remission in acromegaly patients with both initial surgical failure and discrepant biochemical results.

Acromegaly in the elderly patients

BACKGROUND

Acromegaly is a rare disease characterized by a chronic exposition to growth hormone (GH) and insulin-like growth factor-1 (IGF-1), caused in most cases by a pituitary GH-secreting adenoma. Chronic GH excess induces systemic complications (metabolic, cardiovascular, respiratory, neoplastic, and musculoskeletal) and increased mortality if not appropriately treated. Recent epidemiological data report an improved life span of patients with acromegaly probably due to better acromegaly management; additionally, the number of pituitary incidentaloma in general population also increased over time due to more frequent imaging. Therefore, the number of elderly patients, newly diagnosed with acromegaly or in follow-up, is expected to grow in the coming years and clinicians will need to be aware of particularities in managing these patients.

PURPOSE

This review aims to explore different aspects of acromegaly of the elderly patients, focusing on epidemiology, diagnosis, clinical presentation, complications, and management options.

METHODS

Available literature has been assessed through PubMed (data until August 2019) by specific keywords.

CONCLUSIONS

Available data on acromegaly in the elderly patient are sparse, but point to important differences. Further studies are needed comparing elderly with younger patients with acromegaly to better define a tailored diagnostic and therapeutic management.

Predictive factors for responses to primary medical treatment with lanreotide autogel 120 mg in acromegaly: post hoc analyses from the PRIMARYS study

PURPOSE

PRIMARYS (NCT00690898) was a 48-week, open-label, phase 3b study, evaluating treatment with the somatostatin receptor ligand lanreotide autogel (stable dose: 120 mg/28 days) in treatment-naïve patients with growth hormone (GH)-secreting pituitary macroadenoma. This post hoc analysis aimed to evaluate factors predictive of long-term responses.

METHODS

Potential predictive factors evaluated were: sex, age, and body mass index at baseline; and GH, insulin-like growth factor-1 (IGF-1), and tumor volume (TV) at baseline and week 12, using univariate regression analyses. Treatment responses were defined as hormonal control (GH ≤ 2.5 µg/L and age- and sex-normalized IGF-1), tight hormonal control (GH < 1.0 µg/L and normalized IGF-1), or ≥ 20% TV reduction (TVR). Receiver-operating-characteristic (ROC) curves were constructed using predictive factors significant in univariate analyses. Cut-off values for predicting treatment responses at 12 months were derived by maximizing the Youden index (J).

RESULTS

At baseline, older age, female sex, and lower IGF-1 levels were associated with an increased probability of achieving long-term hormonal control. ROC area-under-the curve (AUC) values for hormonal control were high for week-12 GH and IGF-1 levels (0.87 and 0.93, respectively); associated cut-off values were 1.19 μg/L and 110% of the upper limit of normal (ULN), respectively. Results were similar for tight hormonal control (AUC values: 0.92 [GH] and 0.87 [IGF-1]; cut-off values: 1.11 μg/L and 125% ULN, respectively). AUC and J values associated with TVR were low.

CONCLUSIONS

The use of predictive factors at baseline and week 12 of treatment could inform clinical expectations of the long-term efficacy of lanreotide autogel.

Acromegaly in the elderly patient

Acromegaly is an insidious disease, usually resulting from growth hormone hypersecretion by a pituitary adenoma. It is most often diagnosed during the 3rd to 4th decade of life. However, recent studies have shown an increase in the incidence and prevalence of acromegaly in the elderly, probably due to increasing life expectancy. As in the younger population with acromegaly, there is a delay in diagnosis, aggravated by the similarities of the aging process with some of the characteristics of the disease. As can be expected elderly patients with acromegaly have a higher prevalence of comorbidities than younger ones. The diagnostic criteria are the same as for younger patients. Surgical treatment of the pituitary adenoma is the primary therapy of choice unless contraindicated. Somatostatin receptor ligands are generally effective as both primary and postoperative treatment. The prognosis correlates inversely with the patient's age, disease duration and last GH level. Arch Endocrinol Metab. 2019;63(6):638-45.

Hypermethylator Phenotype and Ectopic GIP Receptor in GNAS Mutation-Negative Somatotropinomas

CONTEXT

Besides GNAS gene mutations, the molecular pathogenesis of somatotroph adenomas responsible for gigantism and acromegaly remains elusive.

OBJECTIVE

To investigate alternative driver events in somatotroph tumorigenesis, focusing on a subgroup of acromegalic patients with a paradoxical increase in growth hormone (GH) secretion after oral glucose, resulting from ectopic glucose-dependent insulinotropic polypeptide receptor (GIPR) expression in their somatotropinomas.

DESIGN, SETTING, AND PATIENTS

We performed combined molecular analyses, including array-comparative genomic hybridization, RNA/DNA fluorescence in situ hybridization, and RRBS DNA methylation analysis on 41 somatotropinoma samples from 38 patients with acromegaly and three sporadic giants. Ten patients displayed paradoxical GH responses to oral glucose.

RESULTS

GIPR expression was detected in 13 samples (32%), including all 10 samples from patients with paradoxical GH responses. All GIPR-expressing somatotropinomas were negative for GNAS mutations. GIPR expression occurred through transcriptional activation of a single allele of the GIPR gene in all GIPR-expressing samples, except in two tetraploid samples, where expression occurred from two alleles per nucleus. In addition to extensive 19q duplications, we detected in four samples GIPR locus microamplifications in a certain proportion of nuclei. We identified an overall hypermethylator phenotype in GIPR-expressing samples compared with GNAS-mutated adenomas. In particular, we observed hypermethylation in the GIPR gene body, likely driving its ectopic expression.

CONCLUSIONS

We describe a distinct molecular subclass of somatotropinomas, clinically revealed by a paradoxical increase of GH to oral glucose related to pituitary GIPR expression. This ectopic GIPR expression occurred through hypomorphic transcriptional activation and is likely driven by GIPR gene microamplifications and DNA methylation abnormalities.

Growth Hormone Response to Oral Glucose Load: From Normal to Pathological Conditions

The exact physiological basis of acute growth hormone (GH) suppression by oral glucose is not fully understood. Glucose-mediated increase in hypothalamic somatostatin seems to be the most plausible explanation. Attempts to better understand its underlying mechanisms are compromised by species disparities in the response of GH to glucose load. While in humans, glucose inhibits GH release, the acute elevation of circulating glucose levels in rats has either no effect on GH secretion or may be stimulatory. Likewise, chronic hyperglycemia alters GH release in both humans and rats nonetheless in opposite directions. Several factors influence nadir GH concentrations including, age, gender, body mass index, pubertal age, and the type of assay used. Besides the classical suppressive effects of glucose on GH release, a paradoxical GH increase to oral glucose may be observed in around one third of patients with acromegaly as well as in various other disorders. Though its pathophysiology is poorly characterized, an altered interplay between somatostatin and GH-releasing hormone has been suggested and a link with pituitary ectopic expression of glucose-dependent insulinotropic polypeptide receptor has been recently demonstrated. A better understanding of the dynamics mediating GH response to glucose may allow a more optimal use of the OGTT as a diagnostic tool in various conditions, especially acromegaly.

A Consensus Statement on acromegaly therapeutic outcomes

The 11th Acromegaly Consensus Conference in April 2017 was convened to update recommendations on therapeutic outcomes for patients with acromegaly. Consensus guidelines on the medical management of acromegaly were last published in 2014; since then, new pharmacological agents have been developed and new approaches to treatment sequencing have been considered. Thirty-seven experts in the management of patients with acromegaly reviewed the current literature and assessed changes in drug approvals, clinical practice standards and clinical opinion. They considered current treatment outcome goals with a focus on the impact of current and emerging somatostatin receptor ligands, growth hormone receptor antagonists and dopamine agonists on biochemical, clinical, tumour mass and surgical outcomes. The participants discussed factors that would determine pharmacological choices as well as the proposed place of each agent in the guidelines. We present consensus recommendations highlighting how acromegaly management could be optimized in clinical practice.

Growth hormone: isoforms, clinical aspects and assays interference

The measurement of circulating concentrations of growth hormone (GH) is an indispensable tool in the diagnosis of both GH deficiency and GH excess. GH is a heterogeneous protein composed of several molecular isoforms, but the physiological role of these different isoforms has not yet been fully understood. The 22KD GH (22 K-GH) is the main isoform in circulation, followed by 20KD GH (20 K-GH) and other rare isoforms. Studies have been performed to better understand the biological actions of the different isoforms as well as their importance in pathological conditions. Generally, the non-22 K- and 20 K-GH isoforms are secreted in parallel to 22 K-GH, and only very moderate changes in the ratio between isoforms have been described in some pituitary tumors or during exercise. Therefore, in a diagnostic approach, concentrations of 22 K-GH accurately reflect total GH secretion. On the other hand, the differential recognition of GH isoforms by different GH immunoassays used in clinical routine contributes to the known discrepancy in results from different GH assays. This makes the application of uniform decision limits problematic. Therefore, the worldwide efforts to standardize GH assays include the recommendation to use 22 K-GH specific GH assays calibrated against the pure 22 K-GH reference preparation 98/574. Adoption of this recommendation might lead to improvement in diagnosis and follow-up of pathological conditions, and facilitate the comparison of results from different laboratories.

"Micromegaly": an update on the prevalence of acromegaly with apparently normal GH secretion in the modern era

PURPOSE

Approximately 25 % of cases of clinically active acromegaly cases treated in our academic center between 1996 and 2000, were diagnosed in patients who had elevated plasma IGF-1 levels, but apparently "normal" 24-h mean plasma GH levels. The current study served to update the data for patients with acromegaly referred to our facility, after increasing awareness of this "normal" GH subpopulation throughout the medical community.

METHODS

A retrospective chart review was conducted on 157 patients with acromegaly who underwent resection of a confirmed somatotroph pituitary adenoma at the University of Michigan Health System between the dates of 1 Jan 2001 to 23 Sept 2015.

RESULTS

Overall prevalence of acromegalic patients with "normal" GH levels, defined as GH <4.7 ng/mL, was 31 %. Over time, the percentage of patients with "normal" GH at diagnosis did not decline: 26 % from 2001 to 2005, 19 % from 2006 to 2010, and 47 % from 2011 to 2015. Mean pituitary tumor size was 1.8 ± 0.1 cm for the group with elevated GH, and 1.2 ± 0.1 cm for the group with "normal" GH (p < 0.001). Percent microadenomas was higher in a group with "normal" GH as compared to those with elevated GH (48 vs. 12 %, p < 0.001), and tumors >2 cm in the maximal diameter were encountered more frequently in the group with elevated GH (43 vs. 14 %, p < 0.001).

CONCLUSIONS

Our data show that a substantial percentage of patients with clinical acromegaly have "normal" GH, and therefore strengthens the growing body of evidence which supports the leading role of IGF-1 levels in diagnostic evaluation. At the present time, questions about the natural course of "micromegaly" and treatment benefits compared to the subpopulation with elevated GH levels remain unanswered, but research continues to build on our understanding of the heterogeneous population of individuals.

Mild pituitary phenotype in 3- and 12-month-old Aip-deficient male mice

Germline mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene predispose humans to pituitary adenomas, particularly of the somatotroph lineage. Mice with global heterozygous inactivation of Aip (Aip(+/-)) also develop pituitary adenomas but differ from AIP-mutated patients by the high penetrance of pituitary disease. The endocrine phenotype of these mice is unknown. The aim of this study was to determine the endocrine phenotype of Aip(+/-) mice by assessing the somatic growth, ultradian pattern of GH secretion and IGF1 concentrations of longitudinally followed male mice at 3 and 12 months of age. As the early stages of pituitary tumorigenesis are controversial, we also studied the pituitary histology and somatotroph cell proliferation in these mice. Aip(+/-) mice did not develop gigantism but exhibited a leaner phenotype than wild-type mice. Analysis of GH pulsatility by deconvolution in 12-month-old Aip(+/-) mice showed a mild increase in total GH secretion, a conserved GH pulsatility pattern, but a normal IGF1 concentration. No pituitary adenomas were detected up to 12 months of age. An increased ex vivo response to GHRH of pituitary explants from 3-month-old Aip(+/-) mice, together with areas of enlarged acini identified on reticulin staining in the pituitary of some Aip(+/-) mice, was suggestive of somatotroph hyperplasia. Global heterozygous Aip deficiency in mice is accompanied by subtle increase in GH secretion, which does not result in gigantism. The absence of pituitary adenomas in 12-month-old Aip(+/-) mice in our experimental conditions demonstrates the important phenotypic variability of this congenic mouse model.