Insulinoma — Med2Date

📋 Key Information Summary

📋

Insulinoma is the most common functional pancreatic neuroendocrine tumour, causing endogenous hyperinsulinaemic hypoglycaemia with Whipple's triad.
Incidence is approximately 1–4 per million per year; most are benign solitary adenomas (>90%) located in the pancreas.
Whipple's triad — symptoms of hypoglycaemia, documented plasma glucose <2.8 mmol/L, and resolution with glucose administration — must be demonstrated.
Neuroglycopenic symptoms (confusion, visual disturbance, seizures, loss of consciousness) dominate the clinical picture and may be misdiagnosed as psychiatric or neurological disease.
The 72-hour supervised fast remains the gold standard provocation test for confirming endogenous hyperinsulinaemic hypoglycaemia.
Diagnosis requires demonstration of inappropriate insulin, C-peptide, and proinsulin levels at the time of hypoglycaemia, with sulphonylurea screen negative.
Localisation with CT abdomen, endoscopic ultrasound (EUS), and Ga-68 DOTATATE PET/CT is essential pre-operatively.
Enucleation or distal pancreatectomy is curative in >90% of benign insulinomas; laparoscopic approach is preferred where feasible.
Diazoxide (Proglicem®) is the primary medical therapy for inoperable or recurrent insulinoma; octreotide and everolimus are second-line options.
Malignant insulinomas (<10%) may require debulking surgery, somatostatin analogues, everolimus, peptide receptor radionuclide therapy (PRRT), or systemic chemotherapy.
Patients with multiple endocrine neoplasia type 1 (MEN1) may have multiple insulinomas requiring subtotal pancreatectomy.
Aboriginal and Torres Strait Islander patients may face delayed diagnosis due to remote access barriers and limited endocrine specialist availability.

🎧 Audio Brief

The Pancreas Tumor That Mimics Dementia

A short clinical audio briefing generated from this article — perfect for the commute or ward round.

Introduction & Australian Epidemiology

Insulinoma is the most common functional pancreatic neuroendocrine tumour (pNET), responsible for endogenous hyperinsulinaemic hypoglycaemia. The condition was first described by William J. Mayo in 1927, and surgical cure has been achievable since the first successful enucleation reported in 1929.

The estimated incidence is 1–4 per million per year, accounting for approximately 1–2% of all pancreatic neoplasms. Insulinomas may occur at any age but peak incidence is in the 4th to 6th decades, with a slight female predominance. In Australia, based on population data, approximately 25–100 new cases are diagnosed annually, though underdiagnosis due to misattribution of neuroglycopenic symptoms to psychiatric or neurological conditions is well recognised.

Over 90% of insulinomas are benign, solitary, small (<2 cm), and intrapancreatic. Malignant insulinomas, defined by the presence of metastases (most commonly hepatic), account for 5–10% of cases. Approximately 4–10% of insulinomas occur in the context of multiple endocrine neoplasia type 1 (MEN1), an autosomal dominant syndrome involving the parathyroids, anterior pituitary, and pancreatic islets.

Early diagnosis and surgical resection remain curative in the vast majority of cases. Delayed recognition leads to recurrent severe hypoglycaemia, falls, seizures, cardiac arrhythmias, and potentially irreversible cognitive impairment.

Pathophysiology & Epidemiology

Pathogenesis

Insulinomas arise from the pancreatic beta cells of the islets of Langerhans. They autonomously secrete insulin in an unregulated fashion, independent of the prevailing blood glucose concentration. This leads to inappropriately elevated circulating insulin levels during fasting states, driving glucose uptake into peripheral tissues and suppressing hepatic gluconeogenesis and glycogenolysis.

The molecular pathogenesis involves:

Sporadic insulinomas: Somatic mutations in YY1 (Yin Yang 1) at 14q32 are found in approximately 30% of cases. Recurrent mutations in MEN1, DAXX, ATRX, and TSC2 are also described.
MEN1-associated insulinomas: Germline loss-of-function mutations in the MEN1 tumour suppressor gene (chromosome 11q13) encoding menin, with subsequent somatic loss of heterozygosity. Multiple insulinomas and recurrence are common.
Malignant transformation: Associated with DAXX/ATRX mutations, alternative lengthening of telomeres (ALT), and higher Ki-67 proliferative indices (>5%).

Anatomical Distribution

Insulinomas are distributed roughly equally throughout the head, body, and tail of the pancreas. Ectopic insulinomas (duodenum, peripancreatic tissue) are exceedingly rare (<1%). Most tumours are <2 cm in diameter at diagnosis, which poses challenges for pre-operative localisation.

Australian Context

In Australia, insulinoma management is concentrated in tertiary centres with multidisciplinary neuroendocrine tumour (NET) teams, including endocrinologists, hepatobiliary surgeons, nuclear medicine physicians, and interventional radiologists. Key centres include Royal North Shore Hospital (Sydney), Austin Health (Melbourne), Royal Adelaide Hospital, and Royal Brisbane and Women's Hospital. The South Australian Cancer Registry and Australian Institute of Health and Welfare (AIHW) data capture pNETs under broader pancreatic cancer coding, making precise incidence data difficult to extract.

Clinical Features

Whipple's Triad

The hallmark diagnostic criterion for insulinoma is the presence of Whipple's triad, first described by Allen Oldfather Whipple in 1938:

✅

Whipple's Triad

1. Symptoms consistent with hypoglycaemia (neuroglycopenic and/or adrenergic)
2. Concomitant low plasma glucose at the time of symptoms (<2.8 mmol/L; or <3.0 mmol/L in the context of a supervised fast)
3. Relief of symptoms upon administration of glucose

Whipple's triad should be demonstrated in a controlled setting (inpatient supervised fast) before proceeding with invasive investigations.

Symptom Classification

Symptoms of insulinoma-related hypoglycaemia can be categorised into two groups:

Symptom Category	Features	Mechanism
Neuroglycopenic	Confusion, difficulty concentrating, abnormal behaviour, visual blurring/diplopia, dysarthria, seizures, loss of consciousness, coma	Cerebral glucose deprivation — the brain depends almost exclusively on glucose; cognitive function fails below ~3.0 mmol/L
Autonomic (Adrenergic)	Tremor, palpitations, sweating, hunger, anxiety, pallor	Counter-regulatory catecholamine release (adrenaline, noradrenaline) in response to falling glucose

⚠️

Diagnostic pitfall: Neuroglycopenic symptoms often precede or occur without adrenergic symptoms, especially after prolonged hypoglycaemia. This leads to frequent misdiagnosis as epilepsy, transient ischaemic attack, psychiatric illness (anxiety, panic disorder, factitious disorder), or dementia. A high index of suspicion is required in any patient with unexplained episodic neurological or psychiatric symptoms.

Temporal Pattern

Symptoms typically occur in the fasting state, particularly in the morning before breakfast or during prolonged physical activity. However, postprandial symptoms can occur. Patients frequently self-medicate with frequent carbohydrate-rich meals, leading to weight gain (reported in 20–40% of patients at diagnosis).

Investigations

Phase 1 — Biochemical Confirmation

The 72-hour supervised fast (also termed the prolonged fast test) remains the gold standard for confirming endogenous hyperinsulinaemic hypoglycaemia.

72-Hour Supervised Fast Protocol

Hour 0

Patient commences fast after last meal. Capillary blood glucose monitoring every 4–6 hours. Serum samples for glucose, insulin, C-peptide, proinsulin, and beta-hydroxybutyrate drawn at baseline and at any symptomatic episode or glucose <3.0 mmol/L.

Hours 0–48

Continue fasting with water and non-caloric beverages permitted. Monitor for symptoms. Suppression of ketogenesis (beta-hydroxybutyrate <2.7 mmol/L) suggests hyperinsulinaemia.

Any time glucose <2.8 mmol/L (or <3.0 with symptoms)

Draw critical sample: plasma glucose, serum insulin, C-peptide, proinsulin, sulphonylurea screen, beta-hydroxybutyrate. Administer IV 50% dextrose immediately if symptomatic.

Hour 72 (if no event)

Draw final samples even if glucose remains above threshold. Consider terminating fast with critical sample if glucose 2.8–3.0 mmol/L and asymptomatic, then re-feed.

Diagnostic Criteria During Fast

Parameter	Diagnostic Threshold	Interpretation
Plasma glucose	<2.8 mmol/L (venous, glucose oxidase)	Confirms hypoglycaemia
Serum insulin	≥36 pmol/L (≥6 μU/mL) at time of hypoglycaemia	Inappropriately non-suppressed
C-peptide	≥200 pmol/L (≥0.6 ng/mL)	Endogenous insulin production confirmed
Proinsulin	≥5 pmol/L	Elevated in insulinoma
Beta-hydroxybutyrate	<2.7 mmol/L	Insulin suppresses ketogenesis; low levels confirm hyperinsulinaemia
Sulphonylurea screen	Negative	Excludes factitious hypoglycaemia or surreptitious drug use

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Essential: A serum sulphonylurea screen (glibenclamide, glipizide, gliclazide, glimepiride) must be performed on the critical sample to exclude factitious hypoglycaemia. False-negative C-peptide suppression with exogenous insulin administration is the differential for low C-peptide with high insulin — but sulphonylurea ingestion produces high C-peptide mimicking insulinoma.

Phase 2 — Tumour Localisation

Once biochemical confirmation of hyperinsulinaemic hypoglycaemia is established, tumour localisation is essential for surgical planning. Insulinomas are often small (<2 cm) and require multimodal imaging.

Available

Contrast-enhanced CT abdomen (pancreatic protocol)

First-line localisation; sensitivity 60–80% for lesions >1 cm. Four-phase pancreatic protocol with arterial and portal venous phases recommended. MBS Item 56500 (CT abdomen).

Specialist

Endoscopic ultrasound (EUS)

Sensitivity 80–95%; superior for small (<2 cm) and pancreatic head lesions. Allows simultaneous fine-needle aspiration (FNA) for histology. Requires experienced endosonographer. Available at major Australian tertiary centres.

Specialist

Ga-68 DOTATATE PET/CT

Emerging as highly sensitive for pNET localisation. Targets somatostatin receptor expression. Available at Austin Health, Royal North Shore, Royal Adelaide, and Peter MacCallum Cancer Centre. PBS authority may be required.

Specialist

MRI abdomen (diffusion-weighted)

Alternative if CT contraindicated (e.g., contrast allergy). Sensitivity 70–85%. MBS Item 63024.

Referral

Selective arterial calcium stimulation with hepatic venous sampling (SACSHS)

Reserved for occult insulinomas not localised by non-invasive imaging. Invasive procedure requiring interventional radiology. Sensitivity 80–90%. Available at selected centres (Royal North Shore Hospital, Austin Health).

Histopathology

Histological confirmation is obtained from the surgical specimen. Immunohistochemistry is positive for insulin, chromogranin A, and synaptophysin. Ki-67 proliferative index is critical for grading (WHO classification of NETs): G1 (<2%), G2 (2–20%), G3 (>20%).

Management

Surgical Management (Definitive Therapy)

Surgical resection is the definitive treatment for insulinoma and is curative in >90% of benign, sporadic cases. The approach depends on tumour size, location, and number.

Surgical Approach	Indication	Key Details
Enucleation	Solitary, superficial tumour <2 cm, not encroaching on main pancreatic duct	Preferred when feasible; lower risk of pancreatic insufficiency. Laparoscopic enucleation increasingly performed in Australia.
Distal pancreatectomy ± splenectomy	Tumours in body/tail, or >2 cm, or close to main duct	Spleen-preserving distal pancreatectomy preferred where oncologically appropriate.
Pancreaticoduodenectomy (Whipple's)	Large head/uncinate tumours encroaching on bile duct or pancreatic duct	Higher morbidity; performed at high-volume hepatobiliary centres.
Subtotal (near-total) pancreatectomy	MEN1-associated multiple insulinomas	Risk of surgical diabetes and exocrine insufficiency; requires lifelong endocrine management.

ℹ️

Intraoperative considerations: Intraoperative ultrasound (IOUS) significantly improves localisation of small lesions. Manual palpation by an experienced surgeon at laparotomy identifies 95% of tumours. Frozen section confirmation of the enucleated specimen is mandatory. Intraoperative blood glucose monitoring should demonstrate a rise to >2.8 mmol/L or ≥1.7 mmol/L above pre-excision values within 30–60 minutes of successful resection.

Medical Management

Medical therapy is indicated for: (1) pre-operative glycaemic stabilisation, (2) unresectable or metastatic disease, (3) patients unfit for surgery, and (4) bridging while awaiting surgery.

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Diazoxide

Proglicem® · Hyperglycaemic agent · K_ATP channel opener

Adult dose 3–8 mg/kg/day PO in 2–3 divided doses; start 100 mg TDS and titrate up. Typical range 200–600 mg/day.

Paediatric dose 8–15 mg/kg/day PO in 2–3 divided doses (used primarily for congenital hyperinsulinism)

Route Oral

Mechanism Opens K_ATP channels in beta cells, inhibiting insulin secretion; also has direct extrapancreatic hyperglycaemic effect.

Key ADRs Fluid retention/weight gain (co-prescribe furosemide if needed), hypertrichosis, nausea, hirsutism, hyperuricaemia, tachycardia

Renal adjustment Use with caution in renal impairment; reduce dose. Highly protein-bound — monitor closely.

PBS status Authority Required

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Octreotide (long-acting)

Sandostatin LAR® · Somatostatin analogue

Adult dose 20–30 mg IM every 4 weeks. Start with short-acting octreotide 50–200 μg SC TDS to assess response.

Indication Second-line; more effective if somatostatin receptor-positive (SSTR2/5) on Ga-68 DOTATATE scan.

Key ADRs Gallstones, steatorrhoea, injection site pain, bradycardia

PBS status Restricted Benefit

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Everolimus

Afinitor® · mTOR inhibitor

Adult dose 10 mg PO daily. RADIANT-3 trial demonstrated progression-free survival benefit in advanced pNETs.

Indication Progressive, metastatic, or refractory insulinoma

Key ADRs Stomatitis, pneumonitis, hyperglycaemia, hyperlipidaemia, immunosuppression

PBS status Authority Required

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Sunitinib

Sutent® · Multi-targeted TKI

Adult dose 37.5 mg PO daily. Continuous dosing regimen for pNETs.

Indication Progressive, well-differentiated advanced pNET Alternative to everolimus for metastatic disease.

PBS status Authority Required

Peptide Receptor Radionuclide Therapy (PRRT)

Lu-177 DOTATATE (Lutathera®) is available in Australia for somatostatin receptor-positive gastroenteropancreatic NETs (GEP-NETs). It may be considered for metastatic insulinoma with high somatostatin receptor expression on Ga-68 DOTATATE PET/CT. Available at specialised centres (Peter MacCallum, Austin Health). TGA-registered; PBS listing requires authority application.

Systemic Chemotherapy

For poorly differentiated (G3) or rapidly progressive malignant insulinoma, platinum-based regimens are considered:

Cisplatin + Etoposide: Standard for high-grade (G3) neuroendocrine carcinoma
Temozolomide ± capecitabine: Alternative for well-differentiated progressive disease; activity in pNETs demonstrated in retrospective series
FOLFOX / FOLFIRI: Reserved for refractory disease; limited evidence

Acute Hypoglycaemia Management

1

Conscious patient

Oral glucose 20–30 g (e.g., 200 mL Lucozade®, 4 glucose tablets). Recheck BGL in 15 min. Repeat if BGL remains <4.0 mmol/L.

2

Unconscious or unable to swallow

IV 50% dextrose 50 mL (25 g) bolus via large vein. Follow with 10% dextrose infusion at 100–150 mL/hr. Avoid IM glucagon (stimulates insulin release from insulinoma — may paradoxically worsen hypoglycaemia).

3

Refractory hypoglycaemia

Continuous IV 10–20% dextrose. Consider IV octreotide 50–100 μg bolus to acutely suppress insulin secretion. Urgent endocrine consultation.

Special Populations

👶 Paediatric

Congenital hyperinsulinism (CHI)

Distinct from insulinoma in infancy; caused by ABCC8/KCNJ11 mutations. Diazoxide is first-line (8–15 mg/kg/day). Diazoxide-unresponsive CHI may require near-total pancreatectomy. Refer to paediatric endocrinology centres (RCH Melbourne, Sydney Children's Hospital, QCH Brisbane).

Insulinoma in children

Rare in paediatric age group. Consider MEN1 screening if diagnosed. Surgical enucleation remains curative. Weight-adjusted dosing for all medical therapies.

🤰 Pregnancy

Diagnosis

Insulinoma in pregnancy is exceedingly rare. The 72-hour fast may be modified (shorter fast with more frequent glucose monitoring). Insulin and C-peptide levels are physiologically elevated in pregnancy — interpret with caution.

Management

Surgery (enucleation) in the second trimester is preferred if required. Diazoxide is Category B3 — use with caution; causes neonatal hypertrichosis and fluid retention. Octreotide is Category B3. Frequent small meals may partially control symptoms.

👴 Elderly

Surgical fitness

Increased operative risk from pancreatic surgery. Comprehensive geriatric assessment pre-operatively. Consider medical management with diazoxide if unfit for surgery. Falls prevention critical — hypoglycaemia-related falls are a major morbidity.

Drug interactions

Diazoxide interacts with warfarin (increased INR), antihypertensives (additive hypotension), and diuretics. Review polypharmacy carefully.

🫘 Renal Impairment

Diazoxide

Highly protein-bound (90%); displaced in renal impairment leading to increased free drug. Reduce dose and monitor closely. Fluid retention exacerbated by renal impairment — proactive diuretic use required.

Everolimus

No dose adjustment in mild–moderate renal impairment. Monitor drug levels and renal function.

🫁 Hepatic Impairment

Metastatic hepatic disease

Hepatic metastases from malignant insulinoma may cause hepatic impairment and alter drug metabolism. Everolimus and sunitinib dose adjustment may be required. Consider hepatic arterial embolisation for symptomatic hepatic metastases.

🛡️ Immunocompromised

Everolimus

mTOR inhibitor — causes significant immunosuppression. Monitor for opportunistic infections (PJP prophylaxis considered). Avoid live vaccines. Regular FBC monitoring.

Aboriginal and Torres Strait Islander Health

Aboriginal and Torres Strait Islander Health Considerations

Access to specialist endocrinology

Aboriginal and Torres Strait Islander peoples in remote and very remote areas have limited access to endocrinologists and tertiary NET multidisciplinary teams. Telehealth endocrinology consultations (MBS Items 91822, 91823) should be utilised where available through the Australian Government telehealth programme. Patient-assisted travel schemes (PATS) in NT, QLD, WA, SA, and NSW support travel to metropolitan centres for diagnostic workup and surgery.

Delayed diagnosis

Neuroglycopenic symptoms may be misattributed in remote settings where neurological and psychiatric services are limited. High index of suspicion for unexplained seizures, confusion, or unusual behaviour, particularly in younger adults. Point-of-care blood glucose testing in remote clinics is essential. Consider insulinoma in any patient with recurrent unexplained hypoglycaemia after excluding common causes (diabetes medications, alcohol, liver disease).

Diagnostic infrastructure

72-hour supervised fasts require inpatient admission and are not feasible in remote health centres. Arrangement for transfer to regional or metropolitan hospitals is required. CT and MRI are available at regional centres; EUS and Ga-68 DOTATATE PET/CT are restricted to metropolitan tertiary centres. Blood sample transport to reference laboratories must be planned — samples for insulin, C-peptide, and proinsulin require cold chain transport.

Surgical access

Pancreatic surgery requires high-volume hepatobiliary centres. Aboriginal and Torres Strait Islander patients may face additional barriers including cultural safety in metropolitan hospitals, family separation, language differences, and distrust of the health system. Aboriginal Health Workers and Liaison Officers should be involved in care coordination. Interpreter services should be offered where English is not the patient's first language.

Chronic disease burden

Higher prevalence of type 2 diabetes, obesity, and chronic kidney disease in Aboriginal and Torres Strait Islander populations may complicate hypoglycaemia workup — ensure sulphonylurea ingestion is excluded. Renal impairment may require dose adjustment of diazoxide. Health literacy support and culturally appropriate education materials are essential for post-operative monitoring and medication adherence.

Cultural safety

Engagement with Aboriginal Health Workers, community-controlled health services (ACCHOs), and cultural support is essential. Respect for gender-specific care preferences. Awareness of Sorry Business and its impact on appointment attendance. Flexible follow-up scheduling and outreach services improve outcomes. The RACGP and NACCHO partnership provides frameworks for culturally safe chronic disease management.

📚 References

1. Cryer PE, Axelrod L, Grossman AB, et al. Evaluation and management of adult hypoglycemic disorders: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2009;94(3):709–728.
2. Service FJ, McMahon MM, O'Brien PC, Ballard DJ. Functioning insulinoma — incidence, recurrence, and long-term survival of patients: a 60-year study. Mayo Clin Proc. 1991;66(7):711–719.
3. Placzkowski KA, Vella A, Thompson GB, et al. Secular trends in the presentation and management of functioning insulinoma at the Mayo Clinic, 1987–2007. J Clin Endocrinol Metab. 2009;94(4):1069–1073.
4. Yao JC, Fazio N, Singh S, et al. Everolimus for the treatment of advanced, non-functional neuroendocrine tumours of the lung or gastrointestinal tract (RADIANT-4): a randomised, placebo-controlled, phase 3 study. Lancet. 2016;387(10022):968–977.
5. Raymond E, Dahan L, Raoul JL, et al. Sunitinib malate for the treatment of pancreatic neuroendocrine tumors. N Engl J Med. 2011;364(6):501–513.
6. Strosberg J, El-Haddad G, Wolin E, et al. Phase 3 trial of 177Lu-DOTATATE for midgut neuroendocrine tumors. N Engl J Med. 2017;376(2):125–135.
7. Ramage JK, Ahmed A, Ardill J, et al. Guidelines for the management of gastroenteropancreatic neuroendocrine (including carcinoid) tumours. Gut. 2012;61(1):1–22.
8. Australian Institute of Health and Welfare (AIHW). Cancer data in Australia. Canberra: AIHW; 2024. Available from: https://www.aihw.gov.au/reports/cancer/cancer-data-in-australia
9. Royal Australian College of General Practitioners (RACGP). General practice management of type 2 diabetes: 2016–2018. East Melbourne: RACGP; 2016.
10. Jensen RT, Cadiot G, Brandi ML, et al. ENETS Consensus Guidelines for the management of patients with digestive neuroendocrine neoplasms: functional pancreatic endocrine tumor syndromes. Neuroendocrinology. 2012;95(2):98–119.
11. Abboud B, Boujaoude J. Occult sporadic insulinoma: localization and surgical strategy. World J Gastroenterol. 2008;14(5):657–665.
12. Dimitriadis GK, Weickert MO, Randeva HS, et al. Medical management of secretory syndromes. Neuroendocrinology. 2020;110(9–10):813–826.