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Diseases of the nervous system (DNS) are etiologically diverse, giving rise to myriad conditions both acute and chronic in nature. Neurological disorders may have an insidious onset or have symptoms that are nonspecific, making classification difficult. Early stages of some disorders are characterized by a variable presentation or by subtle signs and symptoms that are difficult to detect or that go unrecognized until function is impaired. Their occurrence may be at birth, which may confer a lifelong disability, or may occur in middle or late life, which may result in progressive disability and death. Some disorders in children may be developmental and may go undetected until the children reach the age at which deficits are assessed. Hence, recognition, diagnosis, and progression of neurological symptoms may affect the true magnitude and observed onset of neurological disorders.

Diagnoses of neurological disorders requires recognition of symptoms, and confirmation with a neurological examination tailored to symptoms and to onset. Diagnostic tests have changed with advances in imaging and electrophysiological testing. Diagnostic clarity has been enhanced by the use of structural imaging techniques [e.g., computerized tomography (CT) and magnetic resonance imaging (MRI)], as well as functional neuroimaging, which utilize surrogates of neuronal activity (e.g., blood oxygenation, glucose metabolism, electrical activity) to facilitate the visualization of brain. Some of the functional studies available are functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and electroencephalography (EEG). Additionally, cognitive tests developed by neuropsychologists have aided in the diagnosis of cognitive decline. Hence, the evaluation of incidence and prevalence over time is difficult due to changing diagnostic criteria and the likelihood of changing classifications and inclusion of milder or early-onset disease, for example, in multiple sclerosis (MS). Epidemiologic trends are impacted by advances in technology and shifting diagnostic practices and one should be mindful of this when assessing the literature.1

The Global Burden of Disease Study (GBD), conducted by the Institute for Health Metrics and Evaluation (IHME), highlights the tremendous morbidity and mortality of neurologic disease and the increasing importance this constellation of conditions has on healthcare costs, services, and policy. Disability Adjusted Life Years (DALYs) are one estimate of the magnitude or burden of disease and while the total estimated DALYs decreased globally by 31% to 32,711 per 100,000 from 1990 to 2017, the DALYs attributed to DNS increased by 14%. This higher morbidity, as well improvements in management of communicable diseases, maternal and neonatal care, and unintentional injuries, has led to diseases of the nervous system rising from 15th in 1990 to the 9th leading cause of DALYs in 2017 (1278–1454 per 100,000).2 Global and U.S. estimates of DALYs from GBD2017 for diseases of the nervous system are listed in Table 58-1. In May of 2019, member states of the World Health Organization agreed to adopt the International Statistical Classification of Diseases (ICD-11), to go into effect in 2022, which reclassifies stroke as neurological rather than cardiovascular.3,4...

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