Background: Neuroglycopenic symptoms in insulinoma could persist for years before localising the source of endogenous hyperinsulinaemia. 90% of insulinomas are sporadic, solitary and < 2 cm in diameter, and can be associated with multiple endocrine neoplasia-1 (MEN-1). Insulinoma is an emerging clinical entity with a huge diagnostic challenge as tumour growth varies from months to years before tumour localisation.
Case Report: A 59-year old woman was referred with intermittent confusion, sweatiness, palpitations, and tremors. Her fasting glucose was 2.1 mmol/L on several occasions without visual changes and galactorrhoea. Thyroid function was normal. Cortisol was 372 nmol/L with raised C-peptide(1085 pmol/L) and failure of suppression of insulin (101 pmol/l). Self-monitored capillary glucose ranged from 2.04.3 mmol/L. Initial non-invasive imaging, including dual phase computed tomography (CT) abdomen and magnetic resonance (MR) imaging of pancreas proved unsuccessful at identifying any tumour. Annual monitoring of fasting gut hormones including insulin, C-peptide and chromogranin A remained consistent with hyperinsulinaemic hypoglycaemia. For 3 years, she adhered to regular meals containing complex carbohydrate, avoiding prolonged fasting with reasonable symptom control, and was reluctant to undergo further investigations. She wasnt able to tolerate a trial of diazoxide. Three years after initial imaging, symptoms became re-emerged uncontrollably. Repeat magnetic resonance imaging of pancreas and post-contrast octreotide scan performed, followed by intraoperative ultrasound. Despite lack of radiological confirmation from initial scans, successful intraoperative endoscopic ultrasound demonstrated 7×6 mm hypoechoic lesion at tail of pancreas. A curative distal pancreatic resection proved vital with histological confirmation of insulinoma. Twenty-four months post-operatively, she remained well with complete resolution of symptoms and no further hypoglycaemia.
Conclusion: Absence of a tumour on serial non-invasive MR imaging modalities does not completely exclude the possibility of insulinoma. Further monitoring in cases of persistent hyperinsulinaemia may require a complete gut hormone profile and consideration of invasive imaging from experts in intraoperative ultrasound.