Insulinoma Induced Hypoglycaemia in a Jamaican Patient
S Chin1, V Popat2, MS Boyne3, C Cochran2, M Tulloch-Reid3
ABSTRACT
Herein reported is the case of a young woman who had hyperinsulinaemic hypoglycaemia which was
biochemically consistent with an insulinoma. Initial imaging was negative and definitive treatment was
delayed until repeat imaging localized the tumour several years later. This case demonstrates the
importance of clinical judgment and biochemical testing in the diagnosis of insulinoma despite negative
imaging.
Hipoglicemia Inducida por Insulinoma en un Paciente de Jamaica
S Chin1, V Popat2, MS Boyne3, C Cochran2, M Tulloch-Reid3
RESUMEN
Aquí se reporta el caso de una joven que presentó hipoglicemia hiperinsulinémica, bioquímicamente
concordante con un insulinoma. La imagen inicial fue negativa y el tratamiento fue retardado hasta
que mediante la repetición de la técnica de imaginología años más tarde localizó el tumor. Este caso
demuestra la importancia de juicio clínico y las pruebas bioquímicas en el diagnóstico del insulinoma,
especialmente frente a la obtención de una imagen negativa.
West Indian Med J 2007; 56 (2): 182
INTRODUCTION
Insulinomas are relatively rare pancreatic endocrine tumours
with an estimated incidence of 4 cases per million a year (1).
Most insulinomas are solitary and benign, however up to
10% may be malignant. Malignant insulinomas tend to occur
more frequently in patients with multiple endocrine neoplasia
Type-1. Patients with insulinomas usually present clinically
with symptoms of fasting hypoglycaemia as a result of inappropriate insulin secretion. The authors report a case of
insulinoma in which an early biochemical diagnosis was
made, but definitive treatment was delayed due to negative
preoperative localization.
CASE REPORT
A 34-year old Afro-Jamaican woman was seen in the
Endocrinology Clinic of the University Hospital of the West
Indies (UHWI) for evaluation of hypoglycaemia. She had
recurrent episodes of generalized weakness, tremulousness
and dizziness for six years. These symptoms occurred severFrom: Department of Medicine1, University Hospital of the West Indies,
Kingston 7, National Institute of Child Health and Human Development2,
National Institutes of Health, Bethesda, Maryland, USA and Tropical
Medicine Research Institute3, The University of the West Indies, Kingston 7,
Jamaica, West Indies.
Correspondence: Dr S Chin, Department of Medicine, The University of the
West Indies, Kingston 7, Jamaica, West Indies. Fax: (876) 977-0632, e-mail:
swardchin@yahoo.com.
West Indian Med J 2007; 56 (2): 182
al times per day and were typically relieved with food. In
order to minimize these episodes, the patient altered her
eating habits, consuming up to eight meals during the day
and also awoke several times throughout the night to eat.
This resulted in significant weight gain over the six-year
period. The patient had no medical illnesses and was previously well. She worked in a fast food restaurant and lived
with her mother who was being treated with glyburide and
metformin for Type-2 diabetes mellitus. She had no personal
or family history of nephrolithiasis, fractures, pituitary tumours or other features suggestive of multiple endocrine
neoplasia Type-1.
Physical examination revealed a healthy-appearing female who was overweight (BMI 29.1 kg/m²). She did not
have acanthosis nigricans and had no peripheral stigmata of
chronic renal or liver disease.
In order to confirm the presence of fasting hypoglycaemia and to determine its aetiology, the patient was admitted to hospital for a supervised 72-hour fast. On presentation to hospital (after an overnight fast of approximately
11 hours), she was experiencing neuroglycopaenic and neurogenic symptoms. At that time, a glucometer reading was
1.8 mmol/L. Venous blood samples were taken and 50%
dextrose was then administered intravenously with immediate resolution of symptoms, thus fulfilling Whipple’s triad.
The laboratory testing confirmed hyperinsulinaemic hypoglycaemia and a sulphonylurea screen was negative (Table
183
Chin et al
1). Proinsulin and ß-hydroxybutyrate tests were unavailable.
The results of liver, renal and thyroid function tests were
Table 1:
Results at termination of supervised fast (UHWI)
Fasting glucose (mmol/L)
Insulin (uIU/ml)
C-peptide (pmol/L)
Chlorpropamide
Tolazamide
Tolbutamide
Glyburide
Glipizide
Acetohexamide
Result
Normal range
2.0
45
1026
None detected
None detected
None detected
None detected
None detected
None detected
< 6.1
6 – 27
298 – 1324
–
–
–
–
–
–
Fig. 1:
Abdominal computed tomography scan showing a 2.9 cm
hypervascular mass in the body of the pancreas.
Fig. 2:
Calcium-stimulated angiogram showing a ‘step-up’ in the proximal
splenic artery (Fig. 2a) and the superior mesenteric artery (Fig. 2b).
normal and she had a normal cortisol response to a short 250mcg ACTH stimulation test.
Based on these biochemical findings, the patient was
diagnosed with an insulinoma. Abdominal imaging with
computed tomography (CT) and magnetic resonance imaging
(MRI) with gadolinium failed to demonstrate a pancreatic
mass, so surgery was not performed. She continued to be
followed in the Endocrinology Clinic and was subsequently
referred to the National Institutes of Health (NIH) five years
after the initial diagnosis for tumour localization and surgery.
At the NIH, the patient underwent supervised fasts on
consecutive days, the results of which are shown in Table 2.
Table 2:
Results of supervised fasts (NIH)
Glucose (mmol/L)
Insulin (uIU/ml)
C-peptide (pmol/L)
Day 1
Start
End
Day 2
Start
End
3.1
127
2286
3.8
56.2
1789
1.3
212
2352
1.2
63
1789
During the first fast, she experienced symptomatic hypoglycaemia after two hours with venous glucose 1.3 mmol/L,
insulin 212 uIU/ml, C-peptide 2352 pmol/L and proinsulin
0.75 ng/mL. This unusually high fasting insulin concentration raised the suspicion of factitious hypoglycaemia due to
exogenous insulin administration or sulphonylurea use. A
sulphonylurea screen was negative and the patient denied insulin use. During the second fast, she became symptomatic
after 12 hours with venous glucose 1.2 mmol/L, insulin 63
uIU/ml and C-peptide 1789 pmol/L. These results were consistent with endogenous hyperinsulinism secondary to an
insulinoma and preoperative localization was undertaken.
Imaging studies performed included an abdominal CT scan
(Fig. 1) which showed a 2.9 cm hypervascular mass in the
body of the pancreas and MRI which showed a contour bulge
in the same area. Calcium-stimulated angiography (Fig. 2)
was then performed, showing a ‘step-up’ in the proximal
splenic artery and the superior mesenteric artery suggestive
of a lesion in the head or neck of the pancreas.
At surgery a 1.8 x 1.5 cm mass was noted at the neck
of the pancreas. Distal pancreatectomy was performed. A
neuroendocrine tumour was confirmed on frozen section and
immunohistochemistry was positive for glucagon, insulin,
chromogranin and synaptophysin and focally positive for
somatostatin (Fig. 3a–3c).
Fig. 3a: The islet cell adenoma at the left contrasts with the normal
pancreas with islets at the right.
Insulinoma Induced Hypoglycaemia
184
symptoms after glucose administration, in the presence of
inappropriately high or normal insulin, proinsulin and Cpeptide (2).
The supervised 72-hour fast is the gold standard test for
the diagnosis of insulinoma. The test is necessary to document hypoglycaemia and its relationship to the patient’s
symptoms, as well as to demonstrate inappropriate insulin
concentration in the face of hypoglycaemia. Levels of plasma glucose, insulin, C-peptide and proinsulin are measured
simultaneously at baseline and at intervals throughout the
fast (Table 3). The fast should be terminated when patients
Table 3:
Fig. 3b: Immunohistochemical stain for insulin in the insulinoma (insulin
stains brown).
Diagnosis interpretation of the results of a 72-hour fast
Diagnosis
Insulin C-peptide
Proinsulin
Sulphonylurea in
plasma or urine
Exogenous
insulin
–
Insulinoma
Sulphonylurea
use
–
+
= increased; = decreased
Fig. 3c: Immunoperoxidase staining: on the right, antibody to insulin, on
the left, antibody to glucagon.
Postoperatively, the patient developed hyperglycaemia
(glucose 13.9 – 16.7 mmol/L) requiring insulin therapy,
initially by intravenous infusion and then by subcutaneous
injections. She was discharged from the NIH on 10 mg
glyburide daily.
On her return to Jamaica, she implemented healthy
lifestyle changes (avoiding sweets and fatty food, doing
regular exercise), resulting in significant weight loss. The
glyburide was discontinued after two months. At her most
recent evaluation, her BMI was 20.7 kg/m2, HbA1c 5.9% and
fasting glucose 5.2 mmol/L. She had impaired glucose tolerance on an oral glucose tolerance test. At the time of writing,
12 months after surgery, she has continued to remain free of
hypoglycaemic symptoms.
DISCUSSION
The diagnosis of insulinoma is based on Whipple’s triad ie
typical symptoms of hypoglycaemia induced by fasting, demonstration of hypoglycaemia (ie plasma glucose # 2.8
mmol/l) at the time of symptoms and prompt reversal of
have symptoms or signs of hypoglycaemia and simultaneously have fasting glucose in the hypoglycaemic range
(# 2.8 mmol/L). At the end, the plasma levels of glucose,
insulin, C peptide, proinsulin, ß-hydroxybutyrate and sulphonylurea are measured. Details of the standardized protocol are available in reviews (3).
It has been proposed that the 48-hour fast should replace the 72-hour fast as the new diagnostic standard (4). In
a retrospective analysis of data from 127 patients with insulinoma, 120 (94.5%) had their fasts terminated by 48 hours.
Seven patients were fasted beyond 48 hours. Re-evaluation
of the data from their fasts revealed that these seven patients
actually had subtle neuroglycopaenic symptoms and glucose
and insulin concentrations diagnostic of insulinoma by 48
hours and could have had earlier termination of their fasts.
Hirshberg et al concluded that with the currently available
insulin and proinsulin assays, the diagnosis of insulinoma can
be made within 48 hours (4). Our patient was hypoglycaemic
prior to the beginning of the first test and when tested at each
of the subsequent occasions became hypoglycaemic within 2
and 12 hours of beginning the fast.
An important differential diagnosis for insulinoma is
factitious hypoglycaemia due to oral hypoglycaemic agents
as both have elevations of insulin and C-peptide. A sulphonylurea screen is thus essential to differentiate sulphonylureainduced hypoglycaemia from that due to insulinoma.
However, current sulphonylurea assays fail to detect the new
generation sulphonylureas (eg glicazide, glimepiride) and
non-sulphonylurea hypoglycaemic agents (ie nateglinide,
repaglanide). There have been at least two published case
reports in which patients had elevated insulin and C-peptide
185
Chin et al
levels, and negative sulphonylurea screens but were subsequently found not to have insulinomas. The underlying problem was factitious hypoglycaemia due to repaglinide in one
case (5) and glimepiride in the other (6).
The possibility of factitious hypoglycaemia was considered in this patient due to unusually high fasting insulin
levels. It was unlikely that she was surreptitiously using
exogenous insulin since she did not have the typical suppression of C-peptide levels (7). Sulphonylurea screens were
negative on repeated occasions, but as discussed previously
she could still have been using newer insulin secretagogues.
Proinsulin is not usually suppressible in patients with insulinoma, but is suppressible in non-insulinoma patients at
the end of the diagnostic fast (4). Consequently, our patient’s
marked, non-suppressible hyperproinsulinaemia (proinsulin
of 0.75ng/mL, normal, 0–0.2) was in keeping with insulinoma rather than factitious hypoglycaemia. The reason for the
unusually high fasting insulin is still not clear. One possible
explanation is that there was some degree of insulin resistance (resulting from weight gain) which contributed to the
high fasting insulin level at baseline.
The reliability of the biochemical data in the diagnosis
of insulinoma is extremely important, because of the relative
ineffectiveness of non-invasive tumour localization techniques, as discussed later. Evaluation of retrospective biochemical data from 46 cases of histologically confirmed insulinoma showed that the insulin concentrations alone were
equivocal in 17% of cases (8). The addition of C-peptide
values clarified the diagnosis in about 50% of the borderline
cases, whilst ketone (ß-hydroxybutyrate) concentrations
were low during the prevailing hypoglycaemia in all cases.
The combination of the three tests was suggested as the most
effective method for the biochemical diagnosis of hypoglycaemia due to insulinoma (8). An increased percentage of the
proinsulin-like component (%PLC) and proinsulin are
characteristic of insulinomas. The older and more cumbersome method, the %PLC, expresses proinsulin values as a
per cent of the total immunoreactive insulin when each component is measured against an anti-insulin antibody. The
newer and less cumbersome method is to measure proinsulin
directly (9). In a series of 98 patients with proven insulinoma, it was found that 85 patients (87%) had proinsulin $ 0.2
ng/ml (10). Proinsulin measurement is especially useful in
making a diagnosis of insulinoma when the tumour retains
some residual sensitivity to glucose and the insulin levels
may become suppressed during hypoglycaemia. Proinsulin
should ideally be measured at the beginning and the
termination of the fast (9).
Once the biochemical diagnosis of insulinoma is
established, localization of the tumour is the next step; this
may be done preoperatively or intra-operatively. Preoperative localization modalities include selective arteriography,
ultrasound, transgastric endoscopy, CT, magnetic resonance
imaging (MRI), radionuclide scanning, transhepatic venous
catheterization and calcium-stimulated angiography with
catheterization of hepatic veins.
Despite the many attempts aimed at localizing
insulinomas, these tumours remain undetected in approximately 40% of patients (11). The need for accurate preoperative localization is a matter of debate. Boukhman et al
evaluated the sensitivities of tumour localization with various
techniques (12). The sensitivities of tumour localization with
arteriography, CT, preoperative ultrasonography, MRI, MRI
with gadolinium contrast, transhepatic venous sampling,
intra-operative palpation of the pancreas and intra-operative
ultrasonography were 47%, 24%, 50%, 30%, 40%, 55%,
76% and 91% respectively. Intra-operative ultrasound was
therefore more sensitive than pre-operative and other intraoperative techniques for localizing insulinoma. Boukhman et
al concluded that the currently available pre-operative
localization tests are not reliable enough to be recommended
when intra-operative ultrasonography is available.
However, most centres recommend some kind of preoperative imaging in order to minimize and guide the surgical
intervention, and to disclose cases of multiple tumours or
metastatic disease (13). In a series of 25 patients with surgically proven insulinomas, selective intra-arterial calcium
stimulation with hepatic venous sampling was the most sensitive of the preoperative localizing studies (88%) (14).
Additional C-peptide gradients may also be helpful in
assessing the location of a tumour (15). The initial imaging
studies for our patient (CT and MRI abdomen) were negative
for a pancreatic mass lesion. Repeat CT and MRI at the NIH
did reveal the tumour, however this was done five years after
the initial study. While it is well known that these modalities
are operator and equipment-dependent, and are expected to
have a higher yield in a highly specialized centre, the five
years time lapse could have resulted in significant growth of
an initially small undetectable tumour to within the limits of
detection. Preoperative localization with selective intra-arterial calcium stimulation was successful in this case.
In conclusion, the diagnosis of insulinoma is based on
clinical suspicion and biochemical testing. Surgery should
not be delayed in the patient with negative imaging studies as
the best means of tumour localization is with intra-operative
ultrasound.
ACKNOWLEDGEMENTS
We thank Dr Philip Gorden of the National Institute of
Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda for his helpful comments in the
preparation of this manuscript. This investigation was supported in part by the Intramural Research Program of the
NIH, NIDDK.
REFERENCES
1.
Service FJ, McMahon MM, O’Brien PC, Ballard DJ. Functioning
insulinoma – incidence, recurrence, and long-term survival of patients:
a 60-year study. Mayo Clin Proc 1991; 66: 711–9.
Insulinoma Induced Hypoglycaemia
2.
3.
4.
5.
6.
7.
8.
9.
Fajans SS, Vinik AI. Insulin-producing islet cell tumors. Endocrinol
Metab Clin North Am 1989; 18: 45–74.
Service FJ. Hypoglycemic disorders. N Engl J Med 1995; 332:
1144–52.
Hirshberg B, Livi A, Bartlett DL, Libutti SK, Alexander HR, Doppman
JL et al. Forty-eight-hour fast: the diagnostic test for insulinoma. J Clin
Endocrinol Metab 2000; 85: 3222–6.
Hirshberg B, Skarulis MC, Pucino F, Csako G, Brennan R, Gorden P.
Repaglinide-induced factitious hypoglycemia. J Clin Endocrinol Metab
2001; 86: 475–7.
Earle KE, Rushakoff RJ, Goldfine ID. Inadvertent sulfonylurea overdosage and hypoglycemia in an elderly woman: failure of serum
hypoglycemia screening Diabetes Technol Ther 2003; 5: 449–51.
Boyne MS, Smikle MF, De La Haye W. Hypoglycaemia – was it all in
the head? West Indian Med J 2002; 51: 124–7.
Chammas NK, Teale JD, Quin JD. Insulinoma: how reliable is the
biochemical evidence? Ann Clin Biochem 2003; 40: 689–93.
Gorden P. Hypoglycemia. In: A Review of Endocrinology: Diagnosis
and Treatment: Foundation for Advanced Education in Higher Sciences
Inc, National Institutes of Health, Bethesda, MD; 2002, 202–15.
186
10. Gorden P, Skarulis MC, Roach P, Comi RJ, Fraker DL, Norton JA et al.
Plasma proinsulin-like component in insulinoma: a 25-year experience.
J Clin Endocrinol Metab 1995; 80: 2884–7.
11. Daggett PR, Goodburn EA, Kurtz AB, Le Quesne LP, Morris DV,
Nabarro JD et al. Is preoperative localisation of insulinomas necessary?
Lancet 1981; 1: 483–6.
12. Boukhman MP, Karam JM, Shaver J, Siperstein AE, DeLorimier AA,
Clark OH. Localization of insulinomas. Arch Surg 1999: 134: 818–23.
13. Nesje LB, Varhaug JE, Husebye ES, Odegaard S. Endoscopic ultrasonography for preoperative diagnosis and localization of insulinomas.
Scand J Gastroenterol 2002; 37: 732–7.
14. Doppman JL, Chang R, Fraker DL, Norton JA, Alexander HR, Miller
DL, et al. Localization of insulinomas to regions of the pancreas by
intra-arterial stimulation with calcium. Ann Intern Med 1995; 123:
269–73.
15. Sung YM, Do YS, Lee MK, Shin SW, Liu WC, Choo SW, et al.
Selective intra-arterial calcium stimulation with hepatic venous sampling for preoperative localization of insulinomas. Korean J Radiol
2003; 4: 101–8.