Neuroepidemiology

Special Aspects of Neurologic Conditions

The human nervous system comprises the brain, spinal cord, and peripheral nerves. The brain and spinal cord constitute the central nervous system (CNS) while the remainder of the nervous system, including the lumbosacral and brachial plexus, constitute the peripheral nervous system (PNS). Virtually all bodily functions are controlled or regulated by the nervous system, including motor function, sensation perception, memory, thought, consciousness, and basic survival mechanisms such as regulation of heart rate and rhythms and respirations. As such, dysfunction in the nervous system can present with a vast spectrum of physical signs and symptoms, and the potential to misattribute neurologic disorders to other organ system is considerable.

To understand the complexities of neurologic investigations and disorders one must recognize that CNS tissue does not, as a general rule, regenerate or repair particularly well after insult or injury. Recovery is more likely to be mediated by plasticity in the system that allows alternate pathways to assume functions previously held by dead or damaged regions, and such plasticity is most abundant in infants and children, declining substantially with age. Unlike other organ systems, the CNS relies almost exclusively on glucose for metabolic function. The metabolic rate of the brain is extremely high and very vulnerable to injury if nutrients, such as glucose or oxygen, provided through blood flow are disrupted. Anatomically, the nervous system exists in a separate compartment from the rest of the body, being protected from traumatic injury by bony encasement (skull and spinal column) and from exogenous exposures by the blood-brain barrier and the blood-nerve barrier. Anatomic localization of injury or dysfunction in the nervous system is the most critical element in determining symptomatology—‘Where is the lesion?’ is the key mantra physicians address when first assessing a patient with potential neurologic disease, lesion location being one of the most important aspects for the development of a differential diagnosis and ultimately a clinical diagnosis leading to treatment.

Given the nervous system's poor capacity for regeneration, limited plasticity, and anatomic isolation (i.e., encased in the skull and/or spinal column), access to CNS tissue for pathologic diagnosis is often not possible. Since a vast array of physical signs and clinical symptoms can occur as a result of nervous system dysfunction and there is limited opportunity for pathologic diagnosis, expert physician evaluation and/or careful application by trained personnel using validated diagnostic criteria are the most crucial tools for case identification. A worldwide survey of available resources for neurological diagnosis and care conducted by the WHO and the World Federation of Neurology clearly illustrate the devastating lack of health care providers with neurologic expertise in most of the developing world, although developing regions suffer disproportionately from such conditions. Hence, lack of experts either to make the diagnosis or to develop appropriate diagnostic tools for population-based assessment remains a major barrier to neuroepidemiological studies in many regions of the world.

...