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How Prevalent are Neurological Disorders? Two New Studies Count the Ways


  • ✓ Two new studies use the best available evidence to report the incidence of neurological disease in the US and in Ethiopia.

The incidence of neurological disease varies drastically depending on geography and the historical moment, as two papers in the Jan. 30 Neurology demonstrate.

In one, Deborah Hirtz, MD, of the NINDS, and David J. Thurman, MD, MPH, of the Centers for Disease Control and Prevention (CDC), and several colleagues attempt to assess the prevalence of common neurologic disorders in the US using the best available evidence from existing studies (Neurology 2007; 68:326–337).


Dr. Walter A. Rocca: “This information is important for the allocation of research funding and for the planning of services.”

In the other, James H. Bower, MD, and colleagues in the department of neurology at Mayo Clinic in Rochester, MN, attempt to assess “the burden of inpatient neurologic disease in two Ethiopian hospitals,” a paper that highlights the enormous advantages that American neurologists enjoy (Neurology 2007;68:338–342).

Dr. Hirtz and colleagues evaluated the incidence or prevalence of autism, cerebral palsy and Tourette syndrome (common childhood disorders; as well as migraine, epilepsy, stroke, traumatic brain injury, and spinal cord injury, which occur at any age; and Alzheimer disease and Parkinson disease, common disorders later in life. (See “Incidence and Prevalence of 12 Neurologic Disorders.”)

These disorders are not necessarily the most common, according to the authors, but they include those that neurologists are most likely to diagnose and treat. They excluded chronic pain, sleep disorders, vascular dementia, and psychiatric problems.

Among their findings, the prevalence of multiple sclerosis was about 50 percent higher than earlier estimates, due to either better diagnosis or an actual increase in the incidence of the disease; traumatic brain injury decreased by about 50 percent, possibly due, at least in part, to more restrictive hospital admission criteria and improved motor vehicle safety. While death from stroke declined, the data suggest a possible increase in stroke incidence, although some data show a decline in stroke over several decades.


Dr. James H. Bower said Ethiopia, a nation of 71 million people, is served by seven practicing neurologists, adding: “This is a typical situation in many of the nations in Africa.”

“Possible explanations might include more sensitive diagnostic methods using neuroimaging and a significant increase in the proportion of older adults in the population,” they write.

The current rate of Alzheimer disease is substantially higher, probably due to an aging population and better diagnosis, “but the possibility of a real increase in the incidence of dementia merits further research,” the authors write.


Dr. Hirtz said the study was prompted in part by a request for information from the One Voice Coalition (created by the AAN), comprising representatives from major neurological advocacy organizations and support groups.

“It's important for advocates to know the numbers of people who have the disease,” Dr. Hirtz told Neurology Today. “They want accurate information. A lot of the material available gives variable and potentially misleading results. For example, Web sites contain information that may not come from valid sources. Some publications also may have inaccurate information.”

“This information will contribute to decisions about the allocation of resources, so patients might ultimately get more services,” she continued. “For example, if we think there's an increase in the incidence in Alzheimer disease, more resources and support might be given to prevention and treatment.”

Walter A. Rocca, MD, MPH, professor of epidemiology and neurology at the Mayo Clinic College of Medicine, agrees with this assessment. He was not involved in the current study.

“This information is important for the allocation of research funding and for the planning of services,” he said. “It's logical that it comes from investigators working in governmental agencies such as NINDS and the CDC because it provides a public health perspective. I don't think that the principal intended audience is the practicing neurologist, but rather governmental agencies, researchers, policy makers, Congress, managers of medical services — anybody interested in setting medical care priorities. The information is also vital for setting priorities in the pharmaceutical industry.”

Dr. Rocca believes the information could be useful to neurologists, but indirectly. For example, the information would be valuable to a chairperson organizing a department of neurology, or to a neurologist setting up a new practice in an underserved area. A young neurologist in training may use these data to choose a sub-specialty for additional training.

Dr. Rocca said his own research career was guided by similar information on the relative frequency and burden of diseases. “At the beginning of my career I was interested in epilepsy research because I came from a medical school where there were many experts in epilepsy,” he said, “but when I worked at the NIH in the early 80s, I discovered that from a public health perspective the priority was dementia because dementia was more common than epilepsy. Because of the increasing number of people suffering from dementia in an aging population, the term ‘epidemic of dementia’ was used at that time. As a result, I decided to focus my research on dementia and later on Parkinson disease.”


The study on neurologic disease in Ethiopia emerged from the lead author's frequent trips to that country. He and colleagues reviewed records of all medical inpatients admitted over a six-month period to two teaching hospitals, one with neurologists (Tikur Anbessa Hospital of the Addis Ababa University School of Medicine) and one that had none (The Gondar College of Medicine and Health Sciences).

“I've spent time in Ethiopia over the last five years teaching at a medical school,” said Dr. Bower. “I was extremely impressed by the intelligence of the staff, but I was struck by their lack of resources. There was no neurology training program. When I came back, my colleagues at home were incredibly interested in what I was experiencing and had questions, so I felt it might help if I let the developed world know what was happening there.”





Seven practicing neurologists, according to Dr. Bower, serve Ethiopia, a nation of 71 million people. “This is a typical situation in many of the nations in Africa,” Dr. Bower writes.

Among the findings, the authors reported that patients with neurologic disease comprise a minority of medical inpatients, and that noninfectious neurologic disease is at least as common as infectious neurologic disease. (See “Neurologic Syndromes with Outcomes: Ethiopia.”)

That is why he believes it may be more practical for neurologists in African countries to serve as teachers of primary care practitioners rather than providing neurological care themselves.

“The development of local neurology training programs in these countries, by increasing the number of neurology teachers, could potentially make major strides in the care of patients with neurologic disease,” he writes. “Neurologists from developed countries could greatly help their colleagues in the developing world by helping to develop training programs.”

Encouraging physicians in this country to think about providing help was the primary motivation for writing the paper, Dr. Bower told Neurology Today. “I'm hoping they will be excited by it, and recognize a need, and that will spark an interest in helping these countries with training,” he said. “A lot of neurologists would like to help, but they're not surgeons — they can't go in and repair cleft palates. What we can do, however, is teach. We have a lot of knowledge; they have a lot of need.”

W. Allen Hauser, MD, professor of neurology and public health education at Columbia University in New York City, said the paper does not provide much solid information about the prevalence of neurological disorders in Ethiopia. Number one, it's a reflection of who can get to a referral hospital,” he said, “and number two, it's limited by the diagnostic procedures and neurologic expertise available in those hospitals. I suppose one thing it says is that admissions in Ethiopia show no reflection, at least in terms of diagnoses, of what are common neurological conditions in the United States.”

But that, according to Dr. Bower, may have value in itself for neurologists in this country. “I think neurologists will be humbled by my results,” he said. “It may change their perspective. We think our life here is normal everywhere, but we have all these extra resources. I'm not sure that is normal, and I think we forget that.”