Incidence of fractures in patients with multiple sclerosis: the Danish National Health Registers

Background: Hip fractures carry a 12-month excess mortality of up to 20% and often represent a major drop in quality of life. Patients with multiple sclerosis (MS) are at increased risk of osteoporosis and thus fractures from immobilisation and expose to glucocorticoids. Falls may also contribute to fracture risk. However, few studies have reported on incidence of fractures in MS. Objective:To estimate incidence rates of fractures in patients with MS, stratified by fracture type and age, and to compare these rates with healthy controls. Methods: The case population consisted of all patients with an accepted diagnosis of MS in the Danish Multiple Sclerosis Registry (1949-2007). Data were linked to the National Hospital Discharge Register (1996-2007). Patients with MS (11,130 cases) were 1:6 matched by year of birth, gender, calendar time and region to patients without MS (controls). The start of follow-up was defined as 1 January 1996, or if onset of MS happened after this date, as January 1st of the year of first symptoms. Patients were followed up for the occurrence of a first fracture. The incidence rate of fracture was estimated for MS patients as well as for controls as the number of fractures per 1,000 personyears. Results were stratified by fracture type and age categories. An osteoporotic fracture was defined as a fracture of the radius/ ulna, humerus, rib, femur, hip, pelvis, or vertebrae. Incidence rate ratios (IRRs) were calculated by dividing fracture rates in MS patients by fracture rates in controls. Results: Among patients with MS, there were 1,118 osteoporotic fractures during 95,662 person-years, which yielded an incidence rate of 11.7 per 1,000 person-years. For control patients the incidence rate was 7.7 per 1,000 person-years, thus the IRR of osteoporotic fracture between MS patients and controls was 1.52 (95% CI 1.43-1.63). In particular, IRRs of tibia fracture (3.37 (95% CI 2.76-4.12)), femur fracture (6.52 (95% CI 4.96-8.56)) and hip fracture (3.20 (95% CI 2.83-3.62)) were elevated in MS patients versus controls. These fracture types are typically related to immobility. The incidence rate ratio for osteoporotic fracture between MS and non-MS patients first increased with age, up to a ratio of 1.94 (95% CI 1.71-2.20) for patients aged 50-59, and then dropped again. Conclusion: Fractures occurred more often in patients with MS, especially fractures of the tibia, hip and femur.