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Carbohydrate Metabolism and Insulin Resistance in Myotonia Dystrophica

Departments of Medicine and Clinical Neurological Sciences, Faculty of Medicine, University of Western Ontario, and St. Joseph's and University Hospitals London, Ontario, Canada

Address correspondence to: A. J. Hudson, M.D., Dept. of Clinical Neurological Sciences, 339 Windermere Rd., London, Ontario, N6A 5A5 Canada.

Carbohydrate metabolism was studied in fourteen patients with myotonia dystrophica (MD) using oral glucose, fructose and galactose tolerance tests. Insulin responses to tolbutamide, glucagon, arginine and leucine were determined and insulin resistance was measured with exogenous iv insulin. Glucose tolerance was impaired in twelve of the fourteen subjects while hyperinsulinism was found in all patients studied. Insulin response to the various substances was excessive. The insulin tolerance test revealed insulin resistance in all patients and this generally correlated well with the degree of hyperinsulinism to provocative tests. Serum galactose levels after an oral load were much lower in MD compared to normal subjects and were associated with a correspondingly greater rise in glucose, indicating an increased conversion of galactose to glucose. A similar response to oral galactose was found in diabetics. The hyperinsulinism seen with the fructose and galactose tests corresponded well to the rise in glucose during the test. Urinary sorbitol excretion was normal. It is concluded that the impaired carbohydrate metabolism seen in MD is due to peripheral insulin resistance affecting various organs including the liver and it is suggested that the excessive βcell response is secondary to the peripheral resistance.

Supported in part by the Medical Research Council of Canada, Grant #MA-5702.

A portion of this work was presented at the Tenth Canadian Congress of Neurological Sciences, London, Ontario, Canada, June 1975.

Received June 11, 1976.