Diabetes prevalence is unknown in patients with multiple sclerosis (MS). The objective of this study was to estimate the prevalence of both types of diabetes in MS patients. We reviewed the database from our MS center. A total of 1,206 patients were diagnosed and treated at the center for MS in a duration of 6 years (1991–1997). Of those patients, 92 were diagnosed as having diabetes. Health records were reviewed for sex, race, type of diabetes (type 1 versus type 2), age of onset of MS and diabetes, and the presence of family history of diabetes (among first-degree relatives).
The diabetes prevalence was 7.7% in MS patients; 11 patients (0.92% [95% CI 0.38–1.46]) had type 1 diabetes, which is not significantly different from the general population (P = 0.15), and 6.75% (95% CI 6.74–6.76) had type 2 diabetes, which is higher than in the general population at that time (P = 0.0054).
The female-to-male ratio was 1.79 among the diabetic subjects. Among patients with type 2 diabetes, 35% developed diabetes before the diagnosis of MS. However, of those who developed diabetes after the diagnosis of MS, 41.5% were diagnosed in the first 5 years. The mean duration of MS before developing diabetes was 9.9 ± 9.03 (means ± SD) years. We noted a positive family history of diabetes among first-degree relatives of 38% in those with type 2 diabetes and MS. Age distribution of type 2 diabetes shows a peak at the 5th and 6th decades of life. In type 1 diabetes, all patients had diabetes before onset of MS, except one case (diabetes 5 years after MS), with a mean duration of 16.8 ± 11.6 years of diabetes before diagnosis with MS. We also noted a positive family history of diabetes in 36% of patients with type 1 diabetes and MS.
The association of type 1 diabetes with MS may represent only a chance occurrence of two autoimmune diseases. However, both share epidemiological and immunological features and may be primed by virus-induced mechanisms (1). There is also a worldwide north-south prevalence gradient, more common in the northern zones of North America and Europe.
The prevalence of type 2 diabetes was higher in MS patients, probably because of muscle disease from nerve demylination or use of ACTH and glucocorticoids as treatments. Several investigators have found some metabolic disorders linking both diseases, such as abnormalities in fat, calcium, and vitamin D metabolism. Also, there is evidence of disruption of myelin due to changes in glucose levels (2). Whether this observation has implications for a link between diabetes and MS is merely speculative, and further evidence of a relationship should be confirmed.