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Insights into disease may be gained in a variety of different ways. Sometimes epidemiologists, those who study the occurrence of a disease, are able to show that a disease correlates with a specific food, poison, infectious organism, or parasite. A community physician may occasionally notice that he has seen more cases of a disease than might be expected. He might then report the existence of a cluster of cases in his community. Experience indicates that a cluster of a new syndrome is likely to prove significant, as have clusters of AIDS in the last decade or clusters of Legionnaires disease in the previous one. However, clusters of more common diseases observed in communities are likely to provide little information or to have little statistical validity. The authors discuss the statistical problems that make it difficult to determine if an observed cluster is actually related to some aspect of the disease or simply the result of random chance. For example, a physician in a community of 40,000 might suspect that more cases of amyotrophic lateral sclerosis have been seen over the last 10 years than would be expected in a community of this size; analysis of case records may confirm this hunch. To establish that this is a significant cluster of cases, other factors must be considered, such as the geographic stability of the community. If 20 percent of the people in this community move out each year and the same number move in, within approximately 10 years about 120,000 different people will pass through the physicians offices of the community. Three times as many cases of any disease are likely to be seen than would be expected in a population of 40,000. Other considerations may influence the appearance of clusters as well. It would be inappropriate to ignore all reports of disease clusters. Similarly, it would be impossible to follow-up all such reports with a detailed investigation. Careful data analysis is necessary to distinguish the community-based reports of disease clusters that are more likely to yield useful epidemiological insights. (Consumer Summary produced by Reliance Medical Information, Inc.)

Creutzfeldt-Jakob disease (CJD) is a brain disease which leads rapidly and inexorably to dementia, coma, vegetative state, and death. Some cases occur in family clusters, but the majority are sporadic. The disease may be transmitted by the tissues from CJD patients, and the infectious agent appears to be an unusual protein particle dubbed a 'prion,' rather than a conventional virus. The condition is found worldwide, and reports of its incidence range from 0.1 to 1.9 new cases per million people each year. In the 1970s, health officials in Israel observed that 40 percent of the new cases of CJD in that country were from Libya. This would suggest that Libyan Jews have an annual incidence rate of 31 per million, many times higher than anywhere else in the world. This finding directed the attention of health officials to this disease and toward Libyan Jews to determine if the initial finding is indeed true and what possible explanations might account for the observation. A survey was taken of all Jewish patients hospitalized with CJD between 1963 and 1987. In contrast with some illnesses, patients with CJD are invariably hospitalized towards the end of their lives, and thus such a survey is likely to include virtually all cases nationwide. A total of 114 cases were identified in this way. Forty-nine of these patients were born in Libya. The annual incidence rate was found to be 0.9 per million for most Israelis and 43 per million for Libyan Jews. If there were some sort of unidentified exposure in Libya which caused the development of CJD at such a high rate, then immigrants who spent more time there before emigrating should be at higher risk. This was not found, however. Investigating the families of the patients, it was found that 12 Libyan families had more than one case of CJD, in contrast with only two such families that were not of Libyan origin. These observations suggest that the reason for the enormous incidence of Creutzfeldt-Jakob disease among Libyan Jews is, in fact, due to a concentration of families carrying some genetic factor causing or contributing to the disease. (Consumer Summary produced by Reliance Medical Information, Inc.)

Amyotrophic lateral sclerosis (ALS) is sometimes called Lou Gehrig's disease. This disorder affects motor neurons, the nerve cells that control the contraction of muscle cells. As these neurons degenerate, the patient becomes progressively weaker and ultimately dies. In about 80 percent of all cases of ALS, death occurs within five years of the onset of the disease. A curious feature of ALS is that, compared with many other diseases, the incidence (number of new cases) of the disease is essentially constant in all parts of the globe, if one excludes some western Pacific islands where ALS is especially common. Some studies have indicated that the incidence of ALS is increasing. However, it is not certain whether these increases represent a true increase in the disease frequency or an increase in the accuracy with which the disease is being recognized and recorded. A study was conducted to ascertain the number of ALS cases (prevalence) in Harris County, Texas. Cases were identified on the basis of death certificates, the records of neurologists, and records of the Muscular Dystrophy Association. These sources indicated that the incidence of ALS was 1.27 new cases each year per 100,000 men and 1.03 new cases each year per 100,000 women. These rates are lower than some recently reported rates for the northern US, Canada, and northern Europe. Conversely, the rates are higher than those determined by some studies of ALS in southern Europe. No differences were found between blacks and whites. Hispanic men developed ALS at a rate comparable to nonHispanic men. Curiously, however, fewer cases of ALS were found among Hispanic women than would be expected. The overall prevalence of ALS among patients between 65 and 74 years was 33 cases per 100,000 men and 19 per 100,000 women. (Consumer Summary produced by Reliance Medical Information, Inc.)

While the incidence of stroke has declined more than 60 percent in the last 30 years, minorities have not shared proportionately in the improvement. While American whites probably fare better than blacks and other minority groups in most areas of medical care, the disparity may be broader for care of neurological problems. Many black patients prefer the care given by their family physicians, and never see a neurologist, despite transient ischemic attacks (reduced blood supply to the brain), small strokes, multiple sclerosis, or other conditions. Hypertension, a leading cause of strokes, is more common among some minorities; 28 percent of adult blacks suffer from hypertension, in contrast with about 17 percent of adult whites. Not only are blacks more likely to have this important risk factor, but they also have a shorter life expectancy when a stroke actually occurs. That is also true of Parkinson's disease and dementia. Studies have shown that the delay period from the first onset of stroke symptoms to arrival at the hospital is longer for black patients, and the period between arrival at the hospital and examination by a neurologist is longer as well. That is, of course, if a neurologist is seen at all. Unfortunately, gathering data on the availability of health care to minority groups is not easy. In some cases, minority members may refuse neurological treatment because they do not understand them and the procedures are not adequately explained. Lumbar punctures are a source of great trepidation for many, and some people are concerned that magnetic resonance imaging might hurt their brains. Neurologists must shoulder the responsibility for improving the access of minority members to neurological care. Professional neurological societies must also address the problems of minorities within neurology itself. About 12 percent of the American population is black; about four percent of physicians under 40 are black. During the 1980s, 2.5 percent of the neurology residents were black. (Consumer Summary produced by Reliance Medical Information, Inc.)

Amyotrophic lateral sclerosis (ALS), a degenerative neuromuscular disease also known as Lou Gehrig's disease, occurs worldwide. Although there are a few areas where the disease has an especially high or especially low frequency of occurrence, by and large the distribution is quite uniform. In the United States, the disease has been found to be more common among rural residents and also among whites as opposed to nonwhites. Some researchers think that the disease may be related to environmental factors. A geographical analysis of the disease might therefore be expected to show clusters of cases in particular areas. In practice, however, the validity of such clusters might be difficult to establish, since increased numbers of cases might be identified in a particular area simply because of superior neurological services in that region. In an attempt to learn more about the distribution of cases of amyotrophic lateral sclerosis, investigators in England have now accomplished what appears to be the most detailed geographic analysis of the disease to date. Individual cases of ALS were assigned to individual voting districts in the Lancashire and South Cumbria regions. Statistical analysis revealed some clustering; i.e. there were several wards in which there were more cases of ALS than would have been expected by chance alone. Since some neurological diseases, such as Parkinson's disease, show clustering about certain birth years, the ALS cases were analyzed for clustering in time, as well, but no such clustering could be identified. The results lend additional support to the notion that ALS is the result of environmental influences. Some investigators have suggested, however, that ALS is actually a syndrome and not a disease. That is to say, ALS is a collection of symptoms which might well be the final common outcome of a variety of distinct disease processes. (Consumer Summary produced by Reliance Medical Information, Inc.)

Human T-cell lymphotropic virus type I (HTLV-I) is strongly associated with adult T-cell leukemia (ATL). Both the virus and ATL occur frequently in the Caribbean and Central and South America. Previous studies have suggested a possible association between HTLV-I and spastic paraparesis (SP), a demyelinating disease causing paralysis from the waist down. All patients who were newly diagnosed with degenerative nervous system diseases in Panama City between January 1985 and December 1986 were studied to determine if they were infected with HTLV-I. Patients with SP had neurologic problems an average of 8.6 years before seeing a neurologist. SP caused problems chiefly due to loss of spinal cord function, but alterations in spinal and optic nerves were also found. Blood and cerebrospinal fluid samples were tested for HTLV-I by three standard techniques. Of 71 patients, 6 had antibody to HTLV-I. Five of these had SP, while one had multiple sclerosis (MS), but the patients with SP had antibody in cerebrospinal fluid, while the patient with MS did not. Blood samples from family members did not suggest any mechanism by which the infection was transmitted. Sexual partners and children were negative for the virus. In one family, the patient's older brother and parents were positive but had no detectable neurologic abnormalities. However, the incubation period between HTLV-I infection and development of neurologic disease is unknown. Future studies with the new laboratory method, polymerase chain reaction (PCR), may resolve some of these issues. Finally, the incidence of HTLV-I-associated neurologic disease in Panama is greater than that of HTLV-I-associated ATL. (Consumer Summary produced by Reliance Medical Information, Inc.)

Pediatric stroke is an underrecognized, potentially treatable cause of childhood neurologic disease. Acute basilar artery thrombosis is a devastating disease rarely encountered in children. Acute interventions with both chemical and mechanical thrombolysis techniques can improve outcomes in adults with arterial thrombosis of the posterior cerebral circulation. We report a case of intervention with both intra-arterial alteplase (tissue plasminogen activator) and cerebral balloon angioplasty to treat a prolonged basilar artery occlusion secondary to idiopathic thrombosis in an adolescent. Despite the patient being clinically locked-in and intervention being delayed at least 20 hours from symptom onset, he obtained complete neurologic recovery. Issues of pediatric stroke, late therapeutic intervention, chemical thrombolysis, and cerebral angioplasty are discussed. This case highlights the underrecognition and subsequent delay in diagnosis of pediatric stroke and how acute intervention may cure otherwise catastrophic strokes in children. Pediatrics 2003;112:e248-e251. URL: http://www.pediatrics.org/cgi/content/full/112/3/e248; stroke, child, basilar artery, thrombosis, balloon angioplasty, alteplase.