Acromegaly — High-Yield Notes

Source: MyEndoConsult Team

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1. Epidemiology & Etiology

• Incidence: 3–11 per million/year; prevalence ~60 per million (newer data: up to 7.7/million/yr in Iceland, 6.9/100,000 in Italy).
• Equal M:F; typical Dx age 40–60; younger patients = more aggressive disease.
• Diagnostic lag: 5–10 years from symptom onset.
• >99% cases = benign pituitary somatotroph adenoma. Pituitary carcinoma <1%.
• Rare causes: ectopic GHRH (bronchial carcinoid most common peripheral), hypothalamic GHRH (hamartoma, gangliocytoma), ectopic GH (lung, pancreas, adrenal), exogenous GH abuse.
• ~5% familial — MEN1 most common, also McCune-Albright, FIPA, Carney complex.

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2. GH / IGF-1 Physiology — Testable Points

• GH = 191 aa, ~70% circulates as 22 kDa isoform; secreted in pulses (4–11/24h, mostly nocturnal) → single random GH is useless.
• GH receptor → dimerizes → activates JAK2 → STAT5 (also MAPK, PI3K/Akt). Suppressed by SOCS1–3, SHP1/2.
• IGF-1: 70 aa, ~48% homology with proinsulin; binds IGF-1R (similar to insulin R, 1–5% cross-affinity). IGF-1 mostly hepatic, but local paracrine/autocrine IGF-1 drives most growth effects.
• IGF-1 binding: ~99% bound; majority in ternary complex with IGFBP-3 + ALS (150 kDa, half-life 12–15 h vs. 10 min for free IGF-1).

GH Secretion — Stimulators vs. Inhibitors

↑ GH	↓ GH
Sleep, fasting, exercise, stress	Overeating, obesity, aging
Hypoglycemia, ↓FFA, ↑amino acids	Hyperglycemia, ↑FFA, ↑IGF-1
Dopamine, glucagon, sex steroids	Somatostatin
Ghrelin, klotho, GHRH
Pathologic ↑: acute glucocorticoids, T1DM, renal failure, anorexia, cirrhosis, depression	Pathologic ↓: chronic glucocorticoids, hyperthyroidism, T2DM

Pearl: hypothyroidism in children → ↓GH/IGF-1 → short stature; reversed by T4. GH replacement lowers FT4 / raises FT3 via type 2 deiodinase.

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3. Pathology — Adenoma Subtypes (high-yield IHC)

Subtype	Frequency / Features	Behavior
Densely granulated somatotroph	30–40%; eosinophilic; GNAS (Gsα) mutation → ↑cAMP	Older pt, slow-growing, high GH, good SSA response
Sparsely granulated somatotroph	Keratin aggregates (“fibrous bodies”); ↓E-cadherin, ↓SSTR2	Younger, invasive, poor SSA response
Mammosomatotroph	Pit-1 lineage, co-stain GH + PRL	Young, early presentation, good SSA response
Mixed somatotroph/lactotroph	Bihormonal	Recurrence-prone
Mature plurihormonal Pit-1	Stains GH/PRL/TSH, GATA3+	May present with thyrotoxicosis + non-suppressed TSH
Acidophil stem cell	GH+PRL precursor, oncocytic	Hyperprolactinemia disproportionate to size; poor DA response
Poorly differentiated Pit-1	Spindle cells	Macroadenomas, recurrence-prone
Pituitary carcinoma	<1%; Ki67 often >10%; distant mets required for Dx	Temozolomide + RT
Pituitary hyperplasia	Uniform enlargement, no focal enhancement	Look for ectopic GHRH or genetic syndrome

Carcinoma is defined by metastasis, not local invasion.

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4. Clinical Features (organized by system)

Local tumor effects

• Headache (often out of proportion to size), bitemporal hemianopia, cranial nerve palsies.
• Hypopituitarism in ~40% (hypogonadism most common).
• DI is rare in adenomas → suggests invasive/non-adenomatous pathology.

Soft tissue / skeletal

• Coarse features, frontal bossing, prognathism, macroglossia, spade-like hands, ↑ ring/shoe size, dental malocclusion.
• Hyperhidrosis = one of most sensitive signs.
• Skin tags (IGF-1 driven epithelial proliferation), acanthosis, cutis verticis gyrata.
• Vertebral fractures up to 60% (active disease); often deformities > true fractures. Volumetric DXA / TBS > standard DXA for risk.
• Acromegaly arthropathy: widened joint spaces, cartilage hypertrophy, osteophytes (opposite of OA early on); progresses despite biochemical cure.

Cardiovascular (60% of mortality)

• Anti-natriuretic effect of GH on ENaC in cortical collecting duct → volume expansion → HTN (diastolic > systolic).
• Three-phase cardiomyopathy: (1) hyperkinetic concentric hypertrophy → (2) diastolic dysfunction → (3) systolic failure (3–4%, poor prognosis).
• Mitral/aortic regurgitation = irreversible with treatment (cardiomyopathy reversible).
• CMR > echo for fibrosis and RV dysfunction.
• Arrhythmias 7–40%; no clear ↑ in IHD prevalence in recent data.

Sleep / respiratory

• OSA 40–80% (11–20× general population). Soft-tissue (pharyngeal) > bony changes drive it.
• ~40% have persistent OSA after biochemical control.
• Central (non-obstructive) apnea also recognized — direct GH effect on respiratory center.
• ↑ lung volumes, small-airway narrowing, subclinical hypoxemia.

Metabolic

• DM in ~50% at diagnosis; IGT in many more. Insulin resistance ↓ GLUT1/GLUT4, ↑FFA, pro-inflammatory adipose.
• ↑TG, ↓HDL, ↑Lp(a), small dense LDL.

Neoplasia (screening matters)

• ↑ colon polyps & colorectal cancer — right-sided, larger, multiple, more dysplastic.
• ↑ thyroid (papillary), breast, kidney, gastric, bladder in cohorts.
• Multinodular goiter in 70–80%.

Other

• Carpal tunnel ~60% (median nerve swelling itself, not extrinsic compression).
• Hypercoagulable (↑ fibrinogen, factor VIII).
• Renal: ↑GFR, hypercalciuria, hyperphosphaturia, microalbuminuria, glomerulosclerosis (chronic).

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5. Diagnosis

Biochemical (initial)

1. IGF-1 (age- and sex-matched) — first-line screen. Confounded by liver/renal disease, malnutrition, DM, pregnancy.
2. OGTT with GH suppression — gold standard
   • 75 g glucose → GH at 0, 30, 60, 90, 120 (±150) min.
   • Fail to suppress GH <1.0 ng/mL (older) or <0.4 ng/mL (modern ultrasensitive assays) = diagnostic.
   • ~30% show paradoxical rise.
   • False positives: T1DM, cirrhosis, CKD, adolescence, stress, L-dopa, estrogen, opioids.
3. GH day curve — fixed measurable secretion vs. normal undetectable nadirs.
4. TRH test — paradoxical GH rise in ~60% of acromegaly (rarely used now).
5. Co-secretion of PRL in ~1/3 → measure PRL; exclude macroprolactin if elevated.
6. Serum GHRH if ectopic source suspected.

Imaging

• Pituitary MRI with gadolinium = standard.
• >70% macroadenomas at Dx. Younger patients → more invasive.
• T2 hypointensity → densely granulated → good SSA response. T2 hyperintensity → sparsely granulated → poor SSA response.
• Knosp grade ≥3 (crossing lateral tangent of intracavernous/supracavernous ICA) = invasive, lower surgical cure.
• C-11 methionine PET (MET-PET) for residual/persistent disease post-op.
• Gallium-DOTATATE / somatostatin receptor scintigraphy for ectopic GHRH localization.

Post-treatment monitoring criteria (memorize)

Marker	Cutoff	Interpretation
Random GH	<0.4 µg/L	Remission
Random GH	<1.0 µg/L	“Safe,” normalized mortality
OGTT GH nadir	<0.4 µg/L (Endocrine Society)	Remission
OGTT GH nadir	<1.0 µg/L	Good control
IGF-1	Age-/sex-matched normal	Goal
Mean GH on day curve	<2.5 µg/L	Disease control (unreliable post-RT)

Post-op IGF-1 takes ~3 months to normalize → don’t interpret too early. Post-op MRI also at 3 months.

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6. Genetic Syndromes

Syndrome	Gene	Clinical clue
FIPA	AIP (AD)	Young males, high GH, poor SSA response
X-LAG	GPR101 (X-linked)	~80% pre-pubertal acromegaly; mostly female; <5 yo
MEN1	MEN1 (AD)	Pituitary + parathyroid + pancreas. ~6% of MEN1 get GH adenoma
MEN4	CDKN1B (AD)	Pit + parathyroid + pheo + thyroid
Carney complex	PRKAR1A (AD)	Skin lentigines, atrial myxoma, PPNAD-Cushing’s, somatotroph hyperplasia
McCune-Albright	GNAS (mosaic)	Café-au-lait, precocious puberty, fibrous dysplasia; acromegaly in 20–30%
SDH mutations	SDHx (AD)	Pheo/paraganglioma + pituitary
NF1	NF1 (AD)	Optic glioma, rare adenoma

Order AIP testing for any pituitary tumor <30 yo or family history. Order MEN1 if young + hypercalcemia.

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7. Complication Screening (at diagnosis, then…)

Complication	Test	Frequency
HTN	BP ± ABPM	q6 mo
DM	HbA1c, FBG (OGTT in selected)	q6 mo
OSA	Epworth → polysomnography	Annually
Cardiomyopathy	ECG, echo	q3–5 yr if normal
Dyslipidemia	Lipid panel	q6 mo
Colon cancer	Colonoscopy from age 40; rigorous bowel prep (2× normal)	q10y if normal; q3–5y if polyp + ↑IGF-1
Thyroid nodules	Clinical ± US	Annually
Vertebral disease	Spine X-ray / DXA / TBS	At Dx, yearly if symptoms
QoL	AcroQoL	Annually

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8. Management

Goals

1. Normalize GH (<1 µg/L safe, <0.4 µg/L cure) and age-matched IGF-1.
2. Resolve mass effects, preserve pituitary function, prevent recurrence, manage comorbidities.

Surgery — first line for most

• Endoscopic transsphenoidal is now standard.
• Cure rates: microadenoma 70–90%; macroadenoma 30–50%; invasive macro <50%; giant <20%.
• Predictors of cure: smaller size, lower pre-op GH, no cavernous sinus invasion (Knosp 0–2), older age.
• Pre-op SSA can shrink tumor ~50% and improve cardiopulmonary status.
• Complications: transient DI (~5% permanent), CSF leak, meningitis, hypopituitarism.
• Mortality <0.5% in experienced hands.

Medical Therapy

Dopamine agonists (cabergoline)

• Oral; dose 1–4 mg/wk (much higher than for prolactinoma).
• IGF-1 normalization in ~34% (meta-analysis).
• Best use: mild IGF-1 elevation (<2× ULN), co-secreting GH+PRL tumors, combo therapy.

Somatostatin analogues (1st generation: octreotide LAR, lanreotide ATG)

• Bind SSTR2 (and 5).
• ~50–70% achieve safe GH and normal IGF-1.
• Doses: octreotide LAR 10–30 mg q4wk IM; lanreotide ATG 60–120 mg q4wk deep SC.
• AE: GI upset, cholelithiasis (~50% at 2 yrs), hypothyroidism, sinus bradycardia, alopecia (rare), variable glycemic effects.
• Predictors of response: T2 hypointense, densely granulated, SSTR2a+, anti-Cam5.2+ , low Ki67.

Pasireotide LAR (2nd generation SSA)

• Binds SSTR1, 2, 3, 5 (high affinity).
• Slightly better than octreotide in head-to-head; useful in 1st-gen SSA-resistant disease (~20% control).
• Useful for headache control.
• AE: hyperglycemia is the key issue (much worse than 1st-gen).

Oral octreotide — FDA approved; 40–80 mg/day; ~65% maintain control after switch from injectable.

Pegvisomant — GH receptor antagonist

• PEGylated modified GH that blocks receptor dimerization.
• Daily SC; 10–40 mg/day.
• Normalizes IGF-1 in ~90%.
• Cannot use GH to monitor — drug interferes with assay; monitor IGF-1 only.
• AE: LFT abnormalities, injection site reactions, theoretical risk of tumor growth (rarely reported in practice).
• Best use: SSA-resistant disease, diabetic patients (favorable glycemic profile).
• Combinations: SSA + pegvisomant or cabergoline + pegvisomant → IGF-1 control >90%.

Radiotherapy — adjunct

• Used when surgery + medical therapy fail to control disease.
• Conventional fractionated: ~4500 cGy in 25 fractions. GH falls ~50% by 2 yrs; IGF-1 normal in ~60% by 10 yrs.
• Stereotactic (Gamma Knife / SMART): single 15–35 Gy; faster GH fall; ~50% biochemical remission at 5 yrs. Avoid if tumor near optic chiasm.
• Long-term complications: hypopituitarism (most common — 60% hypogonadal, 50% ACTH-deficient, 40% T4-deficient at 10 yr), secondary brain tumors (~2%), radiation optic neuropathy (~5%), CVA (up to 20% at 20 yr), cognitive impairment.

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9. Pearls & Pitfalls

• A single random GH is diagnostically useless — always OGTT or IGF-1.
• Macroglossia, prognathism, supraglottic edema → flag the anesthesiologist; difficult airway.
• OGTT can be falsely positive in T1DM, cirrhosis, CKD, adolescence, stress, estrogen/L-dopa/opioids.
• Valvular disease does not reverse with treatment — cardiomyopathy mostly does.
• Pasireotide → hyperglycemia. Pegvisomant → improves glycemia. Octreotide/lanreotide → neutral-to-mildly worsening.
• Pituitary hyperplasia on histology → hunt for ectopic GHRH (think bronchial carcinoid).
• Pseudoacromegaly differentials: pachydermoperiostosis (HPGD/SLCO2A1 mutations → ↑PGE2), severe insulin resistance syndromes, Marfans, homocystinuria.
• DI in a “pituitary adenoma” → it’s probably not an adenoma (think craniopharyngioma, metastasis, hypophysitis).
• Colonoscopy preparation needs to be doubled — slow transit, elongated colon. Right-sided polyps common → ensure cecum is reached.
• Mortality determinants: age and IGF-1 at diagnosis, treatment modality, malignancy, diagnostic delay.

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10. Quick-Recall Numbers

• Prevalence: ~60/million
• Diagnostic delay: 5–10 years
• Macroadenomas at Dx: >70%
• DM at Dx: ~50%
• OSA: 40–80%
• Carpal tunnel: ~60%
• HTN at Dx (ABPM): ~22%
• Vertebral fractures (active disease): up to 60%
• Cholelithiasis on SSA at 2 yr: ~50%
• Mortality ratio if untreated: ~2× normal
• Surgical cure: micro 70–90%, macro 30–50%, invasive <50%, giant <20%
• Cure cutoffs: GH <0.4 µg/L (cure) / <1.0 µg/L (safe); IGF-1 within age/sex range.

Must-Read References on Acromegaly

1. Katznelson L, Laws ER Jr, Melmed S, et al. Acromegaly: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2014;99(11):3933–3951. doi:10.1210/jc.2014-2700 The foundational US/European guideline. Diagnostic cutoffs, treatment algorithm, pregnancy management. Still the most-cited reference.
2. Fleseriu M, Biller BMK, Freda PU, et al. A Pituitary Society update to acromegaly management guidelines. Pituitary. 2021;24(1):1–13. doi:10.1007/s11102-020-01091-7 The modern update that incorporates oral octreotide, novel combinations, and refined treatment goals. Read with Katznelson 2014 as a pair.
3. Melmed S, Bronstein MD, Chanson P, et al. A Consensus Statement on acromegaly therapeutic outcomes. Nat Rev Endocrinol. 2018;14(9):552–561. doi:10.1038/s41574-018-0058-5 Defines what “controlled” and “cured” mean biochemically and clinically — directly testable cutoffs.
4. Giustina A, Barkan A, Beckers A, et al. A Consensus on the Diagnosis and Treatment of Acromegaly Comorbidities: An Update. J Clin Endocrinol Metab. 2020;105(4):e937–e946. doi:10.1210/clinem/dgz096 The authoritative reference on cardiovascular, metabolic, bone, sleep, and oncologic complications. Screening recommendations originate here.
5. Giustina A, Biermasz NR, Casanueva FF, et al. Consensus on criteria for acromegaly diagnosis and remission. Pituitary. 2024;27(1):7–22. doi:10.1007/s11102-023-01360-1 Most recent international consensus on diagnostic and remission criteria — supersedes older OGTT/IGF-1 thresholds.
6. Colao A, Grasso LFS, Giustina A, et al. Acromegaly. Nat Rev Dis Primers. 2019;5(1):20. doi:10.1038/s41572-019-0071-6 Comprehensive single-source review covering pathogenesis to QoL. Best illustrations and treatment algorithms in the literature.
7. Bolfi F, Neves AF, Boguszewski CL, Nunes-Nogueira VS. Mortality in acromegaly decreased in the last decade: a systematic review and meta-analysis. Eur J Endocrinol. 2018;179(1):59–71. doi:10.1530/EJE-18-0255 Updated mortality data showing normalization with modern multimodal therapy. Replaces older Holdaway 2008 meta-analysis (which is still worth reading for historical context).
8. Melmed S. Acromegaly pathogenesis and treatment. J Clin Invest. 2009;119(11):3189–3202. doi:10.1172/JCI39375 Melmed’s mechanistic review — still the clearest explanation of GH/IGF-1 signaling, somatotroph tumorigenesis, and SSTR pharmacology.
9. Bogusławska A, Korbonits M. Genetics of Acromegaly and Gigantism. J Clin Med. 2021;10(7):1377. doi:10.3390/jcm10071377 Comprehensive review of AIP/FIPA, X-LAG (GPR101), MEN1/4, Carney complex, McCune-Albright, and 3PAs. Includes genetic testing algorithm.
10. Carroll PV, Joshi MN. Acromegaly. In: Feingold KR, et al., eds. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; updated September 7, 2022. Available from: https://www.ncbi.nlm.nih.gov/books/NBK279097/