The Disease Burden

Prompted by estimates of the disease burden first published in 1993, health leaders have begun to recognize the major role of brain disorders in the overall burden of disease.[1,2 and 3] Governments and public health policy makers are starting to investigate the impact of this burden on communities and nations (see, for example, Box 2-1 on the 1999 report of the U.S. Surgeon General). Previous comparisons of the contribution of various disorders to the overall burden of disease were based most commonly on the cause of death alone, or sometimes years of life lost (YLLs) by cause. These comparisons dramatically underestimated the importance of brain disorders because these conditions tend to be chronic (not an acute cause of death) and therefore are rarely listed as the immediate cause of death in official records.[ 2,4] Yet depression, epilepsy, and other brain disorders often cause many years of serious disability. Brain disorders are responsible for at least 27 percent of all years lived with disability (YLDs) in developing countries.1 [5] With the exception of Sub-Saharan Africa, brain disorders are the leading contributors to YLDs in all regions of the world (see Table 2-1).[5]

In these calculations, the disability-adjusted life year, or DALY (a variant of the better known quality-adjusted life years, or QALY), assesses both disability and premature mortality in a single measure. In combining assessments of YLLs and YLDs, current DALY estimates highlight the significant contribution of brain disorders to the overall disease burden in developing countries (see Table 2-2).[5]

Absent data on most developmental disabilities and many adult neurological diseases,2 1998 estimates for brain disorders still show these conditions responsible for nearly 34 percent of all noncommunicable disease DALYs in developing countries (see Figure 2-1). Table 2-2 and Figure 2-2 show the contribution of brain disorders to all DALYs and mortality in developing countries. These conditions account for nearly 15 percent of DALYs and 12 percent of mortality among all disease categories. 3 [6]

Current DALY calculations for developing countries, however, reflect only a portion of the disease burden imposed by brain disorders. These sizable cal-


The percentage distribution of YLDs attributed to brain disorders is estimated using the 1990 data for neuropsychiatric conditions (25.5 percent), the cerebrovascular disease component of cardiovascular disease (approximately one percent), and the self-inflicted injury component of intentional injuries (approximately .5 percent).


Data on such developmental disorders as mental retardation, cerebral palsy, and autism along with adult neurological conditions such as peripheral nerve disease and severe migraine were not accounted for in the estimates of the 1996 Global Burden of Disease study.


Category I: Communicable disease, maternal and perinatal conditions and nutritional deficiencies; Category II: Non-communicable disease; and Category III: Injuries.

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