Usefulness of selective arterial calcium injection test and secretin test in patients with insulinoma

Low-dose Selective Arterial Calcium Stimulation Test for Localizing Insulinoma: A Single-center Experience of Five Consecutive Cases

The selective arterial calcium stimulation test (SACST) is one of the most useful localization tests for insulinoma but can cause false-positive and/or unexpected multi arterial positive results that hamper clinical decisions. There are also several adverse effects, such as nausea and hypoglycemia, at the conventional dose (0.025 mEq/kg) of calcium injection. We herein report five consecutive insulinoma cases in which low-dose (0.005-0.007 mEq/kg) calcium injection for SACST led to successful insulinoma localization. No adverse effects of SACST were observed. In conclusion, a low-dose SACST can be a favorable option as an insulinoma localization test in terms of accuracy and safety.

Diagnosis of functioning pancreaticoduodenal neuroendocrine tumors

Functioning pancreaticoduodenal neuroendocrine tumors (PD-NETs) are popular in a textbook, but they are still unfamiliar to a general clinician, and delay of diagnosis or misdiagnosis has been reported even today. It is a consensus that sporadic functioning PD-NET is cured only by surgical resection. So, early detection and early resection is the gold standard for the treatment of functioning PD-NET. Functioning PD-NETs in patients with multiple endocrine neoplasia type 1 (MEN 1) are often multiple. You should check about MEN 1 whenever you encountered multiple PD-NET. They are diagnosed in younger age than sporadic cases. In most cases they are accompanied with numerous microscopic or macroscopic nonfunctioning P-NETs, which are potentially metastatic and the most common cause of death in MEN 1 patients.

Octreotide-treated diabetes accompanied by endogenous hyperinsulinemic hypoglycemia and protein-losing gastroenteropathy

Occurrence of hypoglycemia in diabetes patients is very rare. We report here a case of frequent hypoglycemic attacks caused by inappropriate endogenous hyperinsulinemia in a female patient with poorly controlled diabetes and protein-losing gastroenteropathy. The blood glucose profiles of the patient were unstable. Results of the fasting test performed to investigate the cause of hypoglycemia suggested endogenous hyperinsulinism. Repeated selective arterial calcium injection tests suggested that hyperinsulinemia might be extrapancreatic in origin. However, efforts to detect a responsible lesion such as insulinoma were unsuccessful. Octreotide was used for the treatment of hypoglycemia and protein-losing gastroenteropathy. After treatment, although her leg edema caused by hypoalbuminemia persisted, hypoglycemia almost disappeared.

A case of secretin-responsive insulinoma with low serum C-peptide levels

Insulinoma is the most common cause of fasting hypoglycemia resulting from autonomous insulin hypersecretion. A 59-year-old woman who had previously had an insulinoma and had undergone a partial pancreatectomy was admitted to our hospital because of recurrence of hypoglycemia after 27 years. She had two unusual endocrinological features: 1) the serum insulin response to intravenous secretin injection was not impaired, and 2) the serum C-peptide levels and ratios of serum C-peptide to insulin were relatively low. Two pancreatic tumors were readily detectable by computed tomography (CT) and magnetic resonance imaging (MRI). The selective arterial calcium injection (SACI) test showed a hyperinsulinemic response by calcium administration to the gastroduodenal artery. A partial pancreatectomy was done and her hypoglycemia disappeared. Histology revealed that the tumors were composed of monotonous, small round cells that were positive for both insulin and cathepsin B. As previous in vitro studies have shown that C-peptide can be metabolized within human insulinoma cells by proteolytic cleavage by cathepsin B, our patient's low serum C-peptide levels might have been caused by degradation of C-peptide by cathepsin B. According to the data from the literature, the molar ratio of serum C-peptide to insulin is generally decreased in patients with insulinoma than normal subjects. This case highlights the need for careful interpretation of C-peptide levels and the intravenous secretin injection test in the diagnosis of insulinoma.

Combining the selective arterial calcium injection test and intraoperative blood glucose monitoring for multiple insulinomas: report of two cases

To date, no precise methods of preoperatively localizing multiple insulinomas or intraoperatively confirming their complete removal have been established. We describe herein the effectiveness of combining the selective arterial calcium injection (SACI) test to locate tumors preoperatively, with intraoperative continuous blood glucose monitoring (IOBGM) to confirm their complete removal. During the 8-year period from 1990 to 1997, we experienced two patients with multiple insulinomas. The first patient required resection of a residual tumor in the remnant pancreas for persistent hyperinsulinemia after a distal pancreatectomy performed under conventional diagnostic procedures. In the second patient, a SACI test was performed in addition to other diagnostic imaging procedures, and while computed tomography scan, endoscopic ultrasonography, and arteriography demonstrated multiple tumors in the body and tail of pancreas, the SACI test suggested that there were also tumors in the head of pancreas. Intraoperative ultrasonography showed a tumor measuring 5 mm in diameter on the surface of the head of the pancreas, apart from the multiple tumors in the body and tail of the pancreas. Complete removal of all tumors was assessed by the hyperglycemic rebound after resection of the tumors, determined by IOBGM. Based upon our experience, we believe that the SACI test and IOBGM are helpful for establishing precise localization and achieving complete removal of multiple insulinomas.

Calcium-evoked insulin release from insulinoma cells is mediated via calcium-sensing receptor

BACKGROUND

We have previously reported that high extracellular calcium ([Ca2+]o) levels elicited rapid increases in the cytosolic free calcium ([Ca2+]i) and insulin release from human insulinoma cells. In this study we further investigated the mechanism for stimulus-secretion coupling of insulinoma cells exposed to high levels of [Ca2+]o.

METHODS

Insulinoma tissues were surgically obtained for primary culture. The changes of [Ca2+]i level in response to various agents were monitored by fluorometry. Total RNA was extracted from tissues and subjected to reverse transcription-polymerase chain reaction (RT-PCR) with calcium-sensing receptor (CaR)-specific primers. PCR products were subcloned and sequenced.

RESULTS

When [Ca2+]o level was elevated, [Ca2+]i in insulinoma cells was immediately increased. Application of neomycin abolished the increase in [Ca2+]i level, although extracellular nifedipine and lanthanum chloride did not affect it. The depletion of intracellular calcium stores with thapsigargin or carbachol eliminated the increase in [Ca2+]i level. RT-PCR analysis identified the 682 bp product, of which the sequence was identical to the corresponding regions of human parathyroid CaR.

CONCLUSIONS

Intracellular Ca2+ release might be important in insulin release from insulinoma cells after exposing to high level of [Ca2+]o. CaR could be involved in this mechanism.