Epidemiology of progressive multiple sclerosis

Abstract

The recognition that the course of MS could show striking variation between patients was made in some of the earliest descriptions of the disease. Whereas the majority of patients follow an initial phase of disease characterized by bouts of relapsing neurological dysfunction, or bout onset MS (BOMS), occurring at unpredictable intervals with variable recovery, a minority of patients exhibit a gradual evolution of symptoms commonly related to spinal cord dysfunction but occasionally cerebellar or cognitive in nature. Despite heated debate and considerable investment in investigative studies, it remains unclear whether patients with primary progressive MS (PPMS) represent a distinct disorder or whether a progressive phase of disease is an inevitable consequence of the evolving pathology of disease, and in particular a reflection of gradual axonal degeneration whose origins lie within a dominant early phase of inflammation and demyelination. The debate is complicated by the fact that, despite recent advances in disease classification, there remains no diagnostic test for MS, let alone its clinical subgroups, and that diagnosis is constructed from probabilistic models of accumulated clinical and paraclinical data. Because of this and recognition of distinct immunological or genetic disorders previously considered to be under the rubric of prior MS disease classifications, it seems likely that additional discrete diseases or disease subgroups will emerge over time, but whether these will include forms of progressive disease remains unclear. In the meantime, the epidemiological data available addressing the progressive phases of disease is wide and varied and able to shed some light on these issues.