Endocrine Abstracts

Introduction: Phaeochromocytomas often induce hyperglycaemia. Few cases are reported with hypoglycaemic fits. The mechanism is unknown. Our findings may indicate a mechanism.

The patient: A 37 year old female had a phaeochromocytoma, with typical characteristics: attacks of headache, nausea and sweating. High blood pressures, up to 237/134. Electrocardiogram indicated ischemia, normal coronary arteries on dynamic CT, normal Echo-Doppler heart examination. HbA1c 6.6%. Fasting glucose 8.8 mmol/l. Plasma metanephrine and normetanephrine, and 24-h-urine adrenaline and noradrenaline were 9, 5, 21, and 3 times upper reference value. MR: phaeochromocytoma (45 mm) in right adrenal. MIBG-scintigraphy: no extraadrenal signal. In addition to this typical presentation she developed frequent fits with hunger, lethargy and visual disturbances, blood glucose 1.8–3.9 mmol/l, induced by sweet meals. A sweet meal challenge gave blood glucose 1.8 mmol/l, and simultaneously high C-peptide and insulin (1012 and 47 pmol/l). Preoperative alphablockade with doxazosin normalised blood pressure and abolished headache, nausea and sweating, while her hypoglycemic fits persisted. β-blocker was intended because of moderate tachycardia and electrocardiographic abnormalities, and considered safe when alphablockade was effective. However, after the first tablet of pranolol 20 mg, she developed a severe attack with hypertension, pallor, headache, vomiting and Takotsubo-cardiomyopathy. The attack was curbed with intravenous nitroglycerin. After removal of her tumour she has been healthy, with normal blood glucose values and without hypoglycemic fits.

Discussion: Normally alphaadrenergic stimulation of β-cells inhibits, while βadrenergic stimulation increases insulin secretion. Three findings may indicate that her catecholamines have caused abnormal βadrenergic stimulation of insulin release: persistence of hypoglycemic fits after alphablockade; unusual response to the small βblocker dose, suggesting an abnormal βadrenergic tone; no fits postoperatively.

Conclusion: Our pheochromocytoma patient had the rare variant with hypoglycemic fits. They were hyperinsulinaemic, possibly caused by excessive βadrenergic stimulation of insulin secretion.