A case of insulin sensitivity
AA Tahrani, AF Macleod & TET West
A 32-year-old woman was referred, at 12 weeks in her second pregnancy, to the antenatal diabetic clinic for control of Type 1 diabetes. HbA1c was 6.5% (4.5-6.2%DCCT).
At 32 weeks gestation she was admitted with premature labour. Treatment with betamethasone resulted in hyperglycaemia. Four days later she was admitted with a suspected subarachnoid haemorrhage. Brain CT was normal. She declined lumbar puncture. Over the next 2 days she developed recurrent hypoglycaemia despite declining insulin doses. She was anorexic and fatigued. Investigation showed no abnormality of renal or feto-placental functions. Free thyroxine, GH and IGF1 concentrations were normal. Cortisol (189 nanomol per litre) and prolactin (372 milliunit per litre) were both low for her stage of pregnancy.
A single oral dose of hydrocortisone (40 milligrams) produced a dramatic improvement in her symptoms. She was continued on hydrocortisone and insulin sensitivity was restored. Investigations one week following delivery, after stopping hydrocortisone for 24 hours, revealed: cortisol 128 nanomol per litre at 1440 h, and normal oestradiol, GH, IGF1, FSH and LH. Dynamic pituitary function tests showed ACTH deficiency (synacthen and CRH tests), but normal thyroid and gonadal function. Pituitary MRI was normal.
Five years later, she developed amenorrhoea and problems with recurrent hypoglycaemia despite continued hydrocortisone and extensive reviews of her diabetic regimen. Investigation revealed hypogonadotrophic hypogonadism and partial growth hormone deficiency (peak GH of 8 milliunit per litre after 1 mg of glucagon. MRI scan was normal. Oestrogen and progesterone replacement therapy was started. A three-month trial of GH therapy resulted in improved energy levels and glycemic control was restored with abolition of hypoglycaemic problems.
This case highlights the need to watch for hypopituitarism in pregnant patients with type I DM who develop recurrent hypoglycemia, as missing the diagnosis can be life-threatening to the mother and child. It is also important to note that replacing growth hormone in patients with diabetes and hypopituitarism is likely to improve hypoglycaemia and may improve the patient's quality of life.