Pancreatic neuroendocrine tumour—insulinoma masquerading as a psychiatric illness

Background

Functioning insulinoma, a rare form of neuroendocrine tumour with 1–4 cases per million population, is following an increasing trend facilitated by better diagnosis.1 2 Usually pancreatic in origin, these insulin-secreting tumours result in episodic hypoglycaemic attack presenting along with autonomic symptoms including tremors, anxiety and diaphoresis and neuroglycopenic symptoms including confusion, visual disturbances, abnormal behaviour and seizures.1 2

Early detection and diagnosis of insulinoma are important in determining the timely successful outcomes of management. However, diagnosis of insulinomas can be challenging given the complexity that not only the symptoms became evident during the fasting state or following exercise but may also be present as postprandial symptoms.3 4 Therefore, delays in the diagnosis of insulinoma and misdiagnosis of symptoms being attributed to psychiatric illness, rare gastrointestinal disturbances, cardiac, or neurological disorders are common.5 This impacts patient’s quality of life (QoL), and the misled diagnosis may lead to severe side effects in mismanaged cases. The diagnosis may require higher modality of PET scan, CT, MRI and endoscopic ultrasound (EUS) among others.

Here, we present a case of insulinoma which was initially misdiagnosed and treated as a psychiatric illness. We report a case of insulinoma of a female patient in her early sixties, who presented with problems of recurrent syncopal attacks over the last 5 years and had been initially managed for an anxiety disorder with psychiatric medications.

Case presentation

The patient initially presented with problems of an episode of loss of consciousness while doing her household work 6 years back. The following day, the patient had an episode of convulsions with tongue bites and involuntary micturition. She was then referred to a tertiary centre in Mangalore city. A neurologist extensively examined her based on several scan reports and EEG and had referred the patient to a psychiatrist. She was started on anxiolytics and then discharged. Following this, the patient had repeated frequent episodes of pre-syncope and syncope, tremulousness and blurring of vision, palpitations. The patient had a compromised QoL with altered abnormal behavioural patterns and sensorial disturbances. She had visited several healthcare consultants at various hospitals. All the while, she was diagnosed to have anxiety and panic attacks and had been treated with antipsychiatric medications.

A year back, her daughter measured blood glucose level during one of those spells and reported it as 40 mg/dL. However, she gave oral sugar at home, patient improved and did not find that important to report to any of the doctors they were consulting. Since then, there has been an increase in her spells of such episodes and her family members considered her problems to be related to some underlying mental illness.

In May 2021, during one of those episodes, she was brought to our hospital in an unconscious state with a low blood sugar level of 43 mg/dL and treated with intravenous 25% dextrose and oral glucose. She was neither on any oral hypoglycaemic agents nor in sepsis. The following day, despite frequent oral administration of a full scoop of glucose, the patient continued to have repeated episodes of hypoglycaemia. Keeping differential diagnosis of neuroendocrine tumour, we further evaluated to confirm our diagnosis.

Investigations

Diagnosis was established by supervised fasting for upto 72 hours with lowest recorded blood sugar level of 37 mg/dL. Concurrent measurements indicated serum insulin was >140.91 (normal level fasting <25 IU/L) and serum C-peptide level was 4.50 ng/mL (normal range 0.81–3.85). The patient had all the features of Whipple’s triad, clinical diagnostic criteria for insulinoma. Accordingly, the patient’s blood sugar level was at <50 mg/dL, had symptoms of hypoglycaemia that resolved on administration of oral glucose or dextrose. EUS was suggestive of a pancreatic hypoechoic lesion (1.5×1.7 cm) in an uncinate process surrounded by vessels (image not shown). Triphasic CT abdomen was suggestive of neuroendocrine tumour. Figure 1 presents the CT findings of the lesion.

Differential diagnosis

NA (as patient was being treated as anxiety disorder and panic disorder for more than 5 years).

Treatment

Provisionally, we diagnosed as insulinoma, a pancreatic neuroendocrine tumour. The patient was started on octreotide injections (50 µg two times a day dosage). Her symptoms improved and the frequency of hypoglycaemic spells was drastically reduced. After 2 months of diagnosis, she was operated by an oncosurgeon, and pylorus preserving pancreaticoduodenectomy was performed. The surgery was successful with the size of tumour <2 cm and there was no evidence of metastasis. Her HPE report corroborated with the findings. Figure 2 presents HPE high power microscopic picture confirming our diagnosis and showing low grade neuroendocrine tumour. Our final diagnosis was a well-differentiated encapsulated grade 1 neuroendocrine tumour of the pancreas with no metastasis evident in other sections of pancreas or lymph nodes. There were no events during her intraoperative and postoperative period stay in hospital and the patient was discharged after 10 days.

Outcome and follow-up

The operation was successful with no postoperative complications. During the subsequent follow-up visits until present, as of November 2021, the patient has not reported any recurrence of hypoglycaemic spells and is observed to be normal.