Endocrine Abstracts

Myotonic Dystrophy is an autosomal dominant multi-system disorder characterised by muscle weakness and myotonia, with associated cardiac, ophthalmic, gastrointestinal and endocrine abnormalities

A 16-year-old boy was referred with a 2 months history of difficulty releasing his hand-grip and problems with swallowing. The clinical diagnosis of myotonic dystrophy 1 was confirmed with genetic testing with the detection of a DMPK expansion mutation. During investigations he was found to have asymptomatic hypoglycaemia, with a random blood glucose value of 2.5 mmol/l and this was confirmed on repeat testing. Further investigations showed a raised random ACTH of 246 ng/ml with a cortisol level of 400 nmol/l. A low dose Synacthen test showed a maximum cortisol response of 441 nmol/l (basal level −399) confirming adrenal insufficiency.

It has been well documented in adults that myotonic dystrophy is associated with multiple metabolic and endocrine abnormalities. There is a four-fold increased prevalence of diabetes associated with hyperinsulinaemia in patients with myotonic dystrophy. Dysregulation of the hypothalamic–pituitary–adrenal axis has also occasionally been described. One previous study of 25 adults with myotonic dystrophy found lower levels of basal cortisol, higher average values of ACTH and a lower cortisol response following stimulation with CRH. This was the pattern of glucocorticoid hypofunction that was seen in our patient. We recommend considering glucocorticoid hypofunction in children with myotonic dystrophy, especially if symptoms of lethargy or hypoglycaemia are noted.