Bone Health in Multiple Sclerosis: Should we be Doing More?

Abstract

Multiple sclerosis (MS) is one of the most common neurodegenerative conditions affecting young adults in the developed world. The precise cause of MS remains unknown; the disease is thought to result from a complex interplay between environ­ mental and genetic risk factors. While MS causes a range of neurological disabilities, which differ between individuals, it is also associated with a significantly increased risk of osteoporosis and fracture. The association between MS, osteo­ porosis and fracture risk was highlighted in the global longitudinal study of osteoporosis in women (the GLOW study) [1]. This large, multinational, observational cohort study of over 60,000 women demonstrated that MS was associated with an age­adjusted hazard ratio (HR) for fracture of 2.0 (95% CI: 1.5–2.8). The only other progressive neuro­ logical disease associated with a significantly increased risk of fracture was Parkinson’s disease (age­adjusted HR: 2.2; 95% CI: 1.6–3.1). The finding of an increased fracture risk in MS has been replicated in other, albeit smaller, databases, which have demonstrated remarkably similar risks [2–4]. The increased fracture risk associated with MS appears to be due, at least in part, to reduced bone mineral density. People with MS have been shown to have reduced bone mineral density at both the femoral neck and lumbar spine [5]. This translates into a significant difference overall in the T­score (used to define osteopenia and osteoporosis) at the femoral neck in people with MS [5]. There has been a widespread assumption that osteoporosis in MS is due to disability and a reduction in weight­bearing exercise. There is certainly evidence of a relation­ ship between disability and bone mineral density in the context of MS – where it has been studied, an inverse correlation exists between the two [5]. However, recent evi­ dence appears to indicate that the situation is more complex than this: a case–control study of 99 newly diagnosed patients with early MS showed that 51% of MS patients exhibited either osteopenia or osteoporosis in at least one skeletal site compared with 37% of controls. This difference was sup­ ported by significantly lower T­scores at both the left femoral hip and lumbar spine in patients with MS in the same cohort [6]. It seems probable that shared etiological factors between low bone mineral density and MS may be at least partly responsible