Insulinoma presenting as postprandial hypoglycaemia
- 1Diabetes and Endocrinology Department, Gatesehad Health NHS Foundation Trust, Gateshead, Tyne and Wear, UK
- 2Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, Tyne and Wear, UK
- Correspondence to Dr Asgar Madathil,
Although insulinoma commonly presents as fasting hypoglycaemia it can rarely present as postprandial hypoglycaemia. We describe a case of insulinoma presenting as postprandial hypoglycaemia and type 2 diabetes mellitus (T2DM). A 60-year-old man presented with a 6 year history of postprandial hypoglycaemic symptoms. A diagnosis of T2DM was made using a standard oral glucose tolerance test to which patient’s postprandial hypoglycaemia was attributed. He was given dietetic advice for postprandial hypoglycaemia and was followed up routinely. After 2 years, hypoglycaemic symptoms worsened by exercise and delayed meals. A number of supervised fasting glucose measurements failed to demonstrate biochemical hypoglycaemia. His insulin, c-peptide and pro-insulin levels were mildly elevated but plasma glucose levels were normal. A CT scan showed 20 mm lesion in the pancreas which was confirmed as insulinoma with pancreatic arterial calcium stimulation studies. Laparoscopic resection confirmed benign insulinoma and hypoglycaemia resolved. Our case illustrates the importance of considering insulinoma as a cause of postprandial hypoglycaemia.
Postprandial hypoglycaemia is often idiopathic, but may follow gastrectomy or gastric bypass procedures. It can also present as an early manifestation of type 2 diabetes mellitus (T2DM). Although insulinoma commonly presents as fasting hypoglycaemia it can rarely present as postprandial hypoglycaemia1 and even less rarely in association with T2DM. We describe a case of insulinoma presenting as postprandial hypoglycaemia and subsequent development of T2DM. This atypical presentation leads to delay in diagnosis and this case report might help to prevent delay in diagnosis of similar cases in the future.
A 60-year-old design engineer presented with a 6 year history of episodes of double vision and loss of concentration occurring postprandially. The attacks he experienced were associated with a fall in capillary blood glucose to below 3 mmol/l and relieved with sugary drinks. He gained 30 kg over that time. His medical history included central obesity, hypertension and atrial fibrillation. He drank alcohol rarely.
Investigation and progress
Prolonged (5 h) oral glucose tolerance test (OGTT) using capillary blood glucose showed no drop in blood sugar. However, his 2 h capillary blood glucose was 11.3 mmol/l. A subsequent standard 2 h OGTT revealed a fasting blood sugar of 5.2 mmol/l and a 2 h value of 11.4 mmol/l. A diagnosis of T2DM was made to which patient’s postprandial hypoglycaemia was attributed. He was given dietetic advice for postprandial hypoglycaemia and was followed up routinely.
Two years later, the patient reported worsening of hypoglycaemic symptoms. He had repeat investigations and this time a 16 h fast in our endocrine unit with a hypoglycaemic event occurring at 16 h and blood glucose of 2.3 mmol/l. His paired serum insulin sample was lost in transit. The 16 h fast was repeated but no drop in plasma glucose was observed. Subsequently, he reported hypoglycaemia when his meals were delayed and after exercise. He underwent a number of supervised fasting glucose measurements but failed to demonstrate biochemical hypoglycaemia. His insulin, c-peptide and pro-insulin levels were mildly elevated but blood glucose levels were normal.
Given his ongoing symptoms, inconclusive biochemistry and high probability of insulinoma, a CT of the pancreas was ordered before a definite biochemical diagnosis was made. It demonstrated a 20 mm hyper vascular lesion in the distal pancreas (figure 1). He was referred to a tertiary endocrine unit for arterial calcium stimulation studies to confirm the functional nature of the lesion. While in the tertiary unit, he had spontaneous symptomatic hypoglycaemia with blood glucose of 1.9 mmol/l and serum insulin of 29.1 mU/l (normal range 1.6–10.9 mU/l). This confirmed hyperinsulinaemic hypoglycaemia. His sulphonylurea screen was negative. A subsequent selective pancreatic arterial stimulation study using calcium gluconate and hepatic venous sampling study performed in the order of least probable to most likely artery to supply insulinoma showed a doubling of serum insulin levels following stimulation via splenic artery which suggested the lesion was situated in the tail of the pancreas as seen on CT. This in effect confirmed preoperatively an insulinoma (figure 2).
A laparoscopic enucleation of the distal pancreatic lesion was performed, histology of which showed a benign insulinoma.
Outcome and follow-up
The patient was free of hypoglycaemic symptoms and lost 6 kgs in weight over a 6 week period postoperatively. A repeat OGTT after 12 months revealed 2 h blood glucose of 11.3 mmol/l suggesting persistence of type 2 diabetes and further OGTT after 36 months revealed normal glucose tolerance indicating remission of T2DM.
Insulinoma as other neuro-endocrine tumours is often difficult to diagnose due to the unpredictable occurrence of symptoms and the need for repeated testing to document endogenous hyperinsulinaemic hypoglycaemia. Initially, it was thought that his postprandial symptoms were related to early stages of diabetes. The patient’s hypoglycaemic symptoms progressed over a 4 year period from pure postprandial to fasting and additional postexercise hypoglycaemia. He was unable to stick to diabetic diet (low in refined carbohydrates) as his symptoms automatically worsened.
The diagnosis of insulinoma in patients suffering with T2DM complicated by central obesity and thus insulin resistance is often difficult. The investigation of suspected insulinoma commonly requires admission to a specialist endocrine unit for prolonged fasting of variable duration ranging from 12 to 72 h depending on clinical circumstances. Hypoglycaemic symptoms may not occur during this period of observed fasting. This is further confounded by inadequate or inappropriate blood sampling during hypoglycaemic episodes. This leads to repeated testing and delayed diagnosis.
Postprandial hypoglycaemia is rarely seen in insulinoma. In a recent case series from the Mayo clinic, only 6% of patients with insulinoma (13 cases out 214) presented exclusively with postprandial hypoglycaemia.1 There was a slight predominance in men, but no other unique clinical features identified this group. The occurrence of T2DM with insulinoma is rare.2,–,5 Insulinoma is often suspected when hypoglycaemia persists despite withdrawal of antihyperglycaemic agents.
Our case illustrates the importance of considering insulinoma as a cause of postprandial hypoglycaemia. A high index of suspicion in patients with postprandial hypoglycaemia who do not respond to conventional treatment or whose pattern of symptoms change will reduce the risk of delayed diagnosis of insulinoma.
▶ Diagnosis of hypoglycaemic disorders is often difficult due to atypical presentations and unpredictable onset of hypoglycaemic symptoms.
▶ Insulinoma can co-exist with T2DM and should be considered when unexplained hypoglycaemia occurs in patients with T2DM.
▶ Insulinoma should be suspected in patients with postprandial hypoglycaemia if not responding to conventional treatment as illustrated in this case.
The endocrine unit, Royal Victoria Infirmary, Newcastle upon Tyne, UK.