Burden of Mental, Neurological, Substance Use Disorders and Self-Harm: Counting the Cards, or Shuffling the Deck?

Abstract

In this issue’s paper entitled: “Burden of Mental, Neurological, Substance Use Disorders and Self-Harm in North America: A Comparative Epidemiology of Canada, Mexico, and the United States,” Vigo et al. provide an alternative perspective on disease-burden estimates from the Global Burden of Disease (GBD) Project. The authors criticize the GBD for what they consider to be an arbitrary reclassification of “mental health-related burden” into other categories and express concern that the GBD approach dilutes the apparent burden attributable to mental health issues. The authors base their reclassification on the creation of a new aggregate category that they call “mental, neurological, substance use disorders and self-harm” (MNSS). MNSS includes suicide mortality, some selected neurological conditions (neurocognitive disorders, epilepsy, and headaches), physical conditions attributable to alcohol, and a proportion of chronic pain issues (to capture the burden of somatic symptom disorders). Analysis of the reclassified data indicates that MNSS is the largest source of disease burden between the ages of 10 and 60. The GBD covers 359 diseases and injuries for 195 countries, with the most recently published estimates covering from 1990 to 2017. The GBD aggregates disease-specific estimates using four hierarchical levels. The fourth level includes burden related to specific disorders (e.g., major depression, dysthymia) although some conditions remain grouped (e.g., anxiety disorders are a Level 4 grouping as of 2017). The third level includes additional aggregation (e.g., depressive disorders), the second level includes a category called “mental disorders,” and at the top of the hierarchy, the first level includes only three overarching categories: noncommunicable diseases; injuries; and communicable, maternal, neonatal, and nutritional diseases. It is these aggregate groupings, and their labeling, that Vigo et al. consider problematic. They point out that the “mental disorders” category does not capture suicide deaths, some relevant neurological morbidity, alcohol-related morbidity, and somatic symptom disorders. Their concern is that the GBD’s approach may reduce “the visibility of the burden related to mental health.” For example, in the 2017 Canadian ranking of disease burden, “mental disorders” rank fifth (although they rank first in the 15 to 24 age range). The purpose of the GBD is to describe mortality and morbidity from health conditions (causes) and risk factors at global, national, and (in some countries, but not in Canada) subnational or regional levels. They make comparisons across populations that enable a better understanding of changing health across the world. While it is not the intention of the GBD to provide an arena in which healthcare sectors compete for resources and prestige, it is possible that naive decision makers, especially those who are unaware of the GBD methodology, could misinterpret GBD estimates in ways that undervalue mental health. For example, some stakeholders may come to believe that the “mental disorders” Level 2 grouping describes, or is intended to describe, mental health-related disease burden in its entirety. Vigo et al. help to counter this risk by producing the MNSS classification—a category that ranks Number 1. Despite some harsh criticisms of the GBD by Vigo et al. (e.g., labeling the aggregate categories as “biased” and lacking in “minimum face validity”), it would be unwise to think of their reanalysis as discrediting the GBD or as correcting errors made by the GBD. Prior to the original GBD report, priority setting in health policy was largely based on causespecific mortality statistics. With the popularization of