Prevalence of Amyotrophic Lateral Sclerosis in Texas, 1998-2003
The Journal – May 2012
By Laurie Wagner, MPH; Natalie P. Archer, MS; Dhelia M. Williamson, PhD; Judith P. Henry, PhD; Randolph Schiffer, MD; and Carlayne E. Jackson, MD
Ms Wagner and Ms Archer, Environmental Epidemiology and Disease Registries Section, Texas Department of State Health Services, Austin, Texas; Dr Williamson, Division of Reproduction Health, Centers for Disease Control and Prevention, Atlanta, Georgia; Dr Henry, Austin/Travis County Health and Human Services District, Austin, Texas; Dr Schiffer, Department of Neuropsychiatry, Texas Tech University Health Sciences Center, Lubbock; and Dr. Jackson, professor, Neurology and Otolaryngology, The Univeristy of Texas Health Science Center, San Antonio, Texas. Send correspondence to Laurie Wagner, MPH, McKing Consulting Corporation, 2900 Chamblee Tucker Rd, Bldg 10, Ste 100, Atlanta, GA 30341; email: lwagner[at]mcking[dot]com.
A prevalence study of amyotrophic lateral sclerosis (ALS) was conducted in 3 areas in Texas to enable the state health department to better respond to community concerns regarding the occurrence of ALS and to contribute to national prevalence estimates. Patients who were diagnosed with ALS by a neurologist were included in the study if they resided in the study areas and had an office visit between January 1, 1998, and December 31, 2003. Point prevalence was calculated by using only those ALS patients known to be alive on December 31, 2003.
A total of 101 persons were identified with ALS in the study areas, and 42 of those were still alive on December 31, 2003. The overall ALS point prevalence was lower than previously published US estimates. Non-Hispanic whites had higher prevalence estimates than Hispanics (2.6 per 100,000 vs 1.0 per 100,000). This study provides ALS prevalence estimates for Texas, including Hispanic populations.
Amyotrophic lateral sclerosis (ALS) is a progressive neuromuscular disorder characterized by the deterioration of both upper and lower motor neurons.1,2 This disorder is the most common form of motor neuron disease and accounts for more than 85% of all cases of motor neuron disease.3,4 Early signs and symptoms of ALS vary depending upon which muscle groups are first affected, but muscle weakness is a hallmark of ALS, which eventually spreads to all four limbs, trunk, abdominal, and facial muscles.5,6
Cases of ALS are rarely seen before age 40 years, and incidence increases with advancing age up to 70 years.7 The median survival time for ALS patients ranges from 3 to 5 years from diagnosis.6 Approximately 25,000 to 30,000 people in the United Sates are estimated to have ALS.2 Annual incidence rates for ALS in the United States range from 1 to 2 cases per 100,000,2,8 and the point prevalence for Western countries has been estimated to be 4 to 6 cases per 100,000 population.9
In much of the United States, including Texas, ALS background prevalence estimates that are timely and specific to the geographic region of concern are not available. Furthermore, few data are available regarding the incidence or prevalence of ALS in specific racial and ethnic groups other than whites in the United States.7,8 The purpose of this study was to obtain sex-, age-, race-, and ethnic-specific point prevalence estimates for ALS in Texas to enable the Texas Department of State Health Services to respond to community concerns regarding the occurrence of this disease, as well as to contribute to national prevalence estimates. This study was approved by the Institutional Review Board of the Texas Department of State Health Services.
Three areas were included in this study: San Antonio (Bexar County) in South Central Texas; El Paso (El Paso County) in West Texas; and the 19-county area surrounding Lubbock in Northwest Texas (Figure). These areas were chosen to obtain ALS estimates in communities with different proportions of residents with Hispanic ethnicity. According to the 2000 census, approximately 78.2% of the population in El Paso County is of Hispanic ethnicity, 54.3% of Bexar County's population is Hispanic, and 33.5% of the Northwest Texas study counties' population is Hispanic.
Patients diagnosed with ALS by a neurologist who resided in any of the study areas and who had an office visit between January 1, 1998, and December 31, 2003, were included in the study. Residence was determined by the address listed in the patient's medical record. All medical records with International Classification of Diseases, 9th Revision (ICD-9) code 335.2 (motor neuron disease) were evaluated for inclusion in the study. Only patients with a diagnosis of ALS were considered for the case count; patients with other forms of motor neuron disease, such as primary lateral sclerosis, progressive muscular atrophy, and spinal muscular atrophy, were excluded. Both sporadic and familial forms of ALS were included in this study.
The source of data for case ascertainment was medical records from the neurology offices and clinics in the study areas. Study investigators contacted medical facilities in each of the study areas to determine if they provided care to ALS patients. Facility participation was defined as either providing access to ALS patients' medical records or stating that no ALS patients were seen at the clinic during the study time period.
If the neurologist or office staff stated that no ALS patients were seen by that facility during the study time period, no further action was taken. If the staff stated that ALS patients were seen at that facility, the study investigators asked to review their medical records. Depending on the facilities of the medical office, ALS patients were identified by either searching electronic billing records or clinical databases for ICD-9 code 335.2 or by having the neurologist or office staff identify ALS patients. Medical records were then pulled and reviewed by study investigators to determine if case inclusion criteria were met.
Demographic information from the medical record was collected on a standardized form by trained abstractors and included name, sex, race and ethnicity, address, and date of birth. Individual identifiers were recorded to avoid duplication of cases. The death status and date of death, if applicable, were ascertained by review of the medical chart, matching the patient's identifying information obtained from the medical chart to identifying information on death certificates, or by asking the neurologist's office to verify the patient's status. Information abstracted from death certificates included name, gender, race and ethnicity, date of birth, date of death, age at death, and place of residence at death.
Crude and age-adjusted ALS point prevalence estimates were calculated by using patients known to be alive on December 31, 2003. Point prevalence was calculated for residents of each study area individually and for all study areas combined. Age-, race and ethnicity-, and sex-specific point prevalence estimates were also calculated for San Antonio (Bexar County) and all study areas combined. The small number of cases identified in El Paso and the 19-county area surrounding Lubbock precluded any stratified analyses being conducted. The number of ALS patients known to be alive on December 31, 2003, was used as the numerator, and 2003 Texas population projection information was used as the denominator.10 Analyses were performed by using SAS, version 9.1, and R, version 2.2.1.
In the 19-county Northwest Texas study area, 6 neurologists' offices, 1 university medical center, and 1 private hospital provided neurological services and care. All participated in this study, although the private hospital was unable to identify patients with ALS who were seen between 2000 and 2003. In El Paso County, 11 neurologists' offices and 1 university medical center provided neurological services and care. All but 1 neurology office participated in this study. In San Antonio, 18 neurologists' offices and 1 university medical center provided neurological services and care. One neurology office did not participate in the study.
The review of medical records identified 104 patients with ALS in the combined study areas. Three cases (2.9%) were found to be duplicates (ie, an individual patient had been seen by more than 1 neurologist); thus, a total of 101 patients met the criteria for the study. Most patients identified resided in San Antonio (83%, n=84), while very few resided in El Paso (10%, n=10) or in the 19-county area surrounding Lubbock (7%, n=7).
Forty-two of the 101 patients with ALS meeting the criteria for the study were alive on December 31, 2003 (San Antonio n=30; El Paso n=7; 19-county Lubbock area n=5). Fifty-one patients were deceased before this time (San Antonio n=46; El Paso n=3; 19-county Lubbock area n=2), and we were unable to ascertain death status for 8 patients. The 42 patients still living on December 31, 2003, were used to calculate ALS point prevalence. Table 1 shows the identification of patients with ALS alive and deceased on December 31, 2003 by study location.
Table 2 shows that point prevalence estimates were similar for both El Paso County (crude 1.0 per 100,000; age-adjusted 1.2 per 100,000) and the Lubbock area (crude 1.2 per 100,000; age-adjusted 1.2 per 100,000), but were higher in San Antonio (crude 2.1 per 100,000; age-adjusted 2.2 per 100,000). The overall crude point prevalence for all study areas combined was 1.6 per 100,000, while the age-adjusted estimate was slightly higher (1.8 per 100,000).
The distribution of ALS cases by sex, age, and race and ethnicity for San Antonio (Bexar County) and all study areas combined are shown in Table 3. Crude point prevalence estimates for ALS were higher for females than for males in both San Antonio (2.3 per 100,000 vs 1.8 per 100,000) and for all study areas combined (1.7 per 100,000 vs 1.5 per 100,000). However, once these estimates were age-adjusted, the slight difference seen between females and males was reduced in San Antonio (2.4 per 100,000 vs 2.1 per 100,000) and disappeared for all study areas combined (1.8 per 100,000 vs 1.8 per 100,000). Prevalence estimates were also higher among patients aged 50 years and older compared with the younger age groups. The highest ALS prevalence estimates were in the group aged 60 to 69 years in both San Antonio (10.7 per 100,000) and in all study areas combined (8.9 per 100,000).
Information on race and ethnicity was missing for 9.5% (n=4) of all ALS cases in this analysis. Of the patients with known race or ethnicity, all except 1 were either Hispanic or non-Hispanic white. Non-Hispanic whites had a higher prevalence of ALS than did Hispanics in both San Antonio (3.4 per 100,000 vs 1.5 per 100,000) and all study areas combined (2.6 per 100,000 vs 1.0 per 100,000). This same pattern was also seen after age-adjusting Hispanic and non-Hispanic white prevalence estimates (Table 3).
This study estimated the prevalence of ALS in 3 diverse geographic areas in Texas. As reported in other studies, higher ALS prevalence estimates were found among non-Hispanic whites and patients aged from 60 to 69 years.11,12 In this study, females had a slightly higher crude point prevalence than did males, which is different than reported in other literature, where males are typically reported as having a slightly higher prevalence compared with females.11-15 Once our rates were age-adjusted, males and females had very similar point prevalence estimates, which also has not been found in other studies.11-15 The overall crude and age-adjusted point prevalence estimates for each of the study areas individually as well as for all study areas combined are lower than point prevalence results reported in other studies.11,12,14-16 This could be due to underascertainment in our study.
San Antonio (Bexar County) had a higher point prevalence than did either the El Paso or Lubbock areas. Most cases in this study were identified in San Antonio (Bexar County), which has a multidisciplinary ALS clinic. Very few cases were identified in the other 2 areas, which do not have an ALS clinic. The increased ALS prevalence in the San Antonio area could be due to differential underascertainment in El Paso County and the 19-county North Texas area as compared with Bexar County, or there could be an actual difference in prevalence among the 3 study areas. Reasons for differences in prevalence among the 3 study areas could include referral and patient migration patterns or differences in the demographic composition of these 3 populations. Reasons for the marked increase in ALS prevalence in San Antonio were not explored in this study.
Although this project generated point prevalences for Texas only, these results are among the first Hispanic-specific ALS prevalence estimates in the United States. Just over one-third of the ALS cases in this analysis were individuals of Hispanic ethnicity. The crude prevalence of ALS among Hispanics was approximately 2.6 times lower than the prevalence for non-Hispanic whites. This difference could be the result of underascertainment of Hispanic cases, underdiagnosis of the disease among Hispanics, or an actual difference in prevalence estimates. Additional studies are warranted to examine the differences in prevalence among ethnicities.
The primary limitation of this study was the possible underascertainment of ALS cases. Two neurology offices in the study areas did not participate, and a private hospital could not provide data for the last 3 years of the study time period. This lack of participation likely led to an underascertainment of ALS cases.
The results of this study provide background prevalence estimates of ALS in 3 geographic areas in Texas as well as much-needed prevalence data for the Hispanic population. We anticipate that these Texas data will contribute to current national prevalence estimates of ALS. Data generated by this project could also help public health officials respond to community concerns about ALS.
We would like to thank the participating offices and clinics whose cooperation made this study possible. We also would like to thank Dr. Casey Barton, Elaine Reynolds, and the ALS Association South Texas Chapter for their assistance with this project. This study was funded by a cooperative agreement with the Agency for Toxic Substances and Disease Registry (Number U50/ATU689131).
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