The Mounting Burden of Neurological Disease

Neurological disorders scrutinized in GDB 2016. Neurological disease and injury outcomes were analyzed in these categories: (1) tetanus, (2) meningitis, (3) encephalitis, (4) stroke, (5) brain and other CNS cancers, (6) traumatic brain injury, (7) spinal cord injury, (8) Alzheimer disease and other dementias, (9) Parkinson disease, (10) multiple sclerosis, (11) motor neuron diseases, (12) idiopathic epilepsy, (13) migraine, (14) tension-type headache, and (15) a residual category of other less common neurological disorders.

Major causes of death and disability. In 2016, the neurological disorders in the analysis accounted for 276 million DALYs (11.6% of global DALYs for all diseases) and, combined, were the underlying cause in 9 million deaths (16.5% of total global deaths). The combined neurological disorders ranked first in causing global DALYs, just ahead of cardiovascular diseases (excluding stroke) and ranked second in causing deaths, just behind cardiovascular diseases.

Growing population and aging drive up the numbers. Since 1990, neurological disorder deaths and DALYs increased by 39% and 15%, respectively, but age-standardized mortality rates and DALY rates decreased by 28% and 27%. Population increase and aging are driving up the numbers, even though the global population is exposed to a lower risk of death from these causes. Decreases in rates and absolute numbers of deaths and DALYs were seen only in infectious neurological disorders (meningitis, encephalitis, and tetanus).

Call for new noncommunicable disorder strategies. The analysis suggests that the prevalence of noncommunicable neurological disorders is likely to continue increasing with the aging of populations and to place added pressure on health care services. Development of new and better strategies to treat or prevent the major neurological disorders and implementation of proven effective prevention strategies for stroke and infectious neurological disorders are recommended.

Top contributing categories. The largest contributor to global neurological DALYs was stroke (42.2%), followed by migraine (16.3%), Alzheimer and other dementias (10.4%), and meningitis (7.9%). Stroke was the leading neurological disorder in age-standardized DALY rates in 19 of 21 GBD world regions. Migraine and Alzheimer disease and other dementias were among the top 4 contributors in all the regions. Spinal cord injury ranked fourth in all 5 high-income regions.

Men vs women. Age-standardized DALY rates were significantly higher in males than in females (male-to-female ratio, 1:12) across the aggregate of 15 neurological disorder categories. The burden was significantly higher in males than in females for traumatic brain injury, Parkinson disease, tetanus, motor neuron diseases, and stroke (male-to-female ratios, ≥ 1.5). Migraine, multiple sclerosis, and tension-type headache were more common and caused greater burden in females (male-to-female ratios, ˂ 0.7).

Timeline for age factor in DALYs. In children aged younger than 5 years, the main causes of neurological DALYs were infectious neurological conditions. Epilepsy DALYs were highest in persons aged 5 to 29 years. Migraine and tension-type headache were large contributors in young and middle-aged adults. Stroke was the dominant cause of neurological burden at 60 to 84 years; stroke burden increased rapidly up to about the age of 80 years. Alzheimer disease and other dementias were the dominant cause of neurological burden in persons aged 90 years and older.

A different story for years of life lost and lived with disability. Years of life lost were the dominant feature of infectious causes, stroke, Alzheimer disease and other dementias, and brain and other CNS cancers. Significant contributors to years lived with disability were headaches, traumatic brain injury, and spinal cord injury (headaches are not considered an underlying cause of death and the International Classification of Diseases [ICD] attributes injury deaths to the cause, not the nature, of injury). Epilepsy, stroke, and Alzheimer disease and other dementias also contributed.

DALYs not risk attributable to all disorders. Fewer than 10% of the DALY burdens are explained by the 84 risks quantified in GBD 2016. Risk-attributable DALYs accounted for 88.8%, 22.3%, and 14.1% of stroke, Alzheimer disease and other dementias, and idiopathic epilepsy DALYs, respectively, but for other disorders the proportion was very small (meningitis, encephalitis, and multiple sclerosis) or zero (tetanus, brain and other CNS cancer, migraine and tension-type headache, and Parkinson disease).