Neuropsychiatric conditions are common throughout the world and account for a substantial portion of the global burden of illness. Over the last decade, the burden of illness attributable to mental health, neurological, and substance use disorders, as measured in disability-adjusted life years (DALYs), has risen dramatically and exceeds the burden of illness attributable to cancer and cardiovascular disease.1 DALYs have been one of the most prominent health metrics used to describe the global burden of mental, neurologic, and substance use disorders. The DALY includes both years lived with disability (YLDs) in addition to years of life lost (YLL).2 Yet there are too few specialized psychiatric and neurologic providers to meet this burden. In many rural and resource-limited settings across the globe, the number of people with neuropsychiatric conditions who do not receive appropriate or adequate treatment for their disorder (defined as the treatment gap) can reach almost 90%.3 There are many structural and operational challenges associated with mental health and neurologic care delivery, including a global scarcity of skilled psychiatric and neurologic practitioners, challenges in effective flow of medical services and goods from manufacturer to patient (defined as supply chain management), limited funding, sociocultural and stigma factors, and weak health systems in many places around the globe. Task sharing—moving care responsibilities from more specialized providers to less specialized health workers—has been increasingly emphasized as one key approach for addressing the global burden of mental disorders; however, this should be combined with improved funding, health system strengthening efforts and training, and engagement of specialized providers in task-shared systems of care. This chapter will provide an overview of the epidemiology and global burden of neuropsychiatric illness and the global neuropsychiatric treatment gap. It will then describe the challenges and potential solutions to effective global mental health service delivery, including current evidence on task-sharing approaches to neuropsychiatric care across the globe.
EPIDEMIOLOGY OF SELECTED NEUROPSYCHIATRIC DISORDERS
Community-based epidemiological studies have estimated that the lifetime prevalence rates of mental disorders in adults globally are 29.2%, and the 12-month prevalence rates of mental disorders are 17.6%.4 In this chapter, the epidemiology of neuropsychiatric disorders will be reported by separating disorders into mental, neurological, and substance use disorders, as is consistent with international literature. Additionally, the epidemiology of neuropsychiatric disorders is commonly investigated in relation to the size of the economy of countries. The World Bank annually classifies national economies by gross national income (GNI), previously known as the gross national product (GDP), via the World Bank Atlas formula in billions of United States dollars (USD). For the 2019 fiscal year, low-income countries (LICs) were defined as <$995 GNI, lower middle-income countries were $996–3895 GNI, upper middle-income countries (UMICSs) were $3896–12,055 GNI, and high-income countries (HICs) were ≥$12,056 GNI.5 The World Bank frequently combines low- and middle-income countries together (LMICs).
Mood Disorders: Major Depressive Disorder and Bipolar Disorder