Epidemiology of neurologically disabling disorders.

Neurological disorders place a considerable burden upon individuals, their families, and society. Some like stroke are common, while others like amyotrophic lateral sclerosis are much rarer. Some conditions such as multiple sclerosis are reported to vary by latitude, while others such as traumatic brain injury can vary considerably by locality. Depending upon the nature of the lesion, and factors such as time since onset, the consequences to the individual may also vary considerably, not just among different disorders, but within a given disorder. Consequently the patterns of disease incidence, its prevalence, and its consequences are complex and may vary not just because of the condition itself, but also because, for example, case ascertainment may vary from study to study. The cumulative annual incidence of disabling neurological disorders is likely to exceed 1000 per 100000, or 1% of the population. The incidence is characterized by significant variation, which is mediated by genetic, geographical, demographic, and environmental factors. While useful comparisons can be made through standardization techniques, planning for local services should be based upon local epidemiology, whenever available.