(CSEMP055) A CASE OF INSULINOMA PRESENTING AS POSTPRANDIAL BIZARRE BEHAVIOUR

Abstract: Insulinomas are rare neuroendocrine tumours that present with sporadic hypoglycemia events. The diagnosis is often delayed 1-3 years after presentation. Loss of the adrenergic counter-regulatory response to hypoglycemia is known as hypoglycemia-associated autonomic failure (HAAF). HAAF can occur with insulinoma, and hypoglycemic events may lack cardinal signs and symptoms. As a result, patients may be misdiagnosed with primary neurologic or psychiatric disease.

A previously healthy 42-year-old woman with a remote history of syncope as a teen presented with an abrupt onset of 6 episodes of exclusively post-prandial bizarre behaviour over a 6-month period. No obvious triggers were identified, but she reported the onset occurring with the diagnosis of terminal cancer in her mother. Episodes occurred 90-120 minutes after eating and resolved spontaneously within 20-30 minutes. The episodes consisted of vocalizations, random limb movements, and unresponsiveness to verbal and tactile cues. The patient could not recall the events but reported feeling irritable prior. She was under investigation for a neurological cause of her paroxysms.

Two of the episodes were documented by EMS. The first episode of bizarre behaviour resolved prior to EMS arrival. Her documented blood glucose (BG) was 3.4 mM, and GCS was 15. With the second event, EMS documented a BG of 1.7 mM and GCS of 6 with normal vitals (pulse 60 bpm). She recovered after IV dextrose. The patient started home BG testing and a low glycemic index diet. Investigations excluded adrenal, thyroid, renal, hepatic, and infectious diseases. Fasting glucose and HbA1c were normal. Home BG testing was normal, and no further spells occurred. She was not taking medications that could cause hypoglycemia. A mixed-meal test was conducted during which serum glucose levels were 2.6-3.7 mM, without any signs or symptoms. She continued her diet and monitoring and was followed closely with no further episodes until 8 months later, the patient was found unresponsive at home with a BG glucose of 1.7 mM. A 72 hr fast documented endogenous insulin hypersecretion with symptomatic hypoglycemia at 12 hrs. Investigations identified a pancreatic lesion. Surgical pathology confirmed a diagnosis of insulinoma.

This case illustrates that insulinoma can present with sporadic post-prandial hypoglycemia and HAAF. We propose that clinicians consider insulinoma as a cause of unexplained behavioural postprandial paroxysms and perform a 72 h fast even when symptoms are well-controlled with dietary modification.