RESEARCH
ARTICLE
Incidence and Prevalence of Parkinson’s Disease Among Navajo People Living in the Navajo Nation Paul H. Gordon, MD, PhD,1* Jason M. Mehal, MPH,2 Robert C. Holman, MS,2 Michael L. Bartholomew, MD,3 James E. Cheek, MD, MPH,4 and Andrew S. Rowland, PhD4 1 Indian Health Service, U.S. Department of Health and Human Services, Northern Navajo Medical Center, Shiprock, New Mexico Division of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, Georgia 3 Division of Epidemiology and Disease Prevention, Office of Public Health Support, Rockville, Maryland 4 Public Health Program, Department of Family and Community Medicine, University of New Mexico Health Sciences Center, Albuquerque
2
ABSTRACT:
Parkinson’s disease (PD) is largely unstudied among American Indians. Unique populations might harbor clues to elusive causes. We describe the incidence and prevalence of PD among Navajo people residing in the Navajo Nation, home to the largest American Indian tribe in the United States. We analyzed 2001-2011 inpatient and outpatient visit data for Navajo people obtained from the Indian Health Service, which provides health care to American Indian people living on the Navajo Reservation. Cases were defined by at least two inpatient or outpatient visits with the diagnosis of PD. Crude and age-adjusted incidence and prevalence rates were calculated overall as well as by age, sex, region of residence, and time period. Five hundred twenty-four Navajo people with median age-at-onset of 74.0 years were diagnosed with PD during the study period, yielding an average annual crude incidence rate of 22.5/100,000. Age-specific incidence was 232.0 for patients 65 years of age or older and 302.0 for 80 years
The etiologies of Parkinson disease (PD), thought to be related to complex genetic and environmental interactions,1,2 are uncertain for most patients.3 Clearer understanding is needed to accelerate the pursuit of neuroprotective therapies. Study methodology differs,
------------------------------------------------------------
*Correspondence to: Dr. Paul H. Gordon, Northern Navajo Medical Center, Medical Staff Office, Hwy 491 North, Shiprock, New Mexico 87420, E-mail: [email protected] Funding agencies: None.
Relevant conflicts of interest/financial disclosures: Nothing to report. Full financial disclosures and author roles may be found in the online version of this article. Received: 13 May 2014; Revised: 3 December 2014; Accepted: 17 December 2014 Published online 4 February 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/mds.26147
714
Movement Disorders, Vol. 30, No. 5, 2015
of age or older. Age-adjusted incidence was 35.9 overall (238.1 for 65 years), was higher in men than in women (47.5 vs. 27.7; P < 0.001), varied by region (P 5 0.03), and was similar between time periods (20022004 vs. 2009-2011). The age-adjusted point prevalence rate was 261.0. The rate of PD among Navajo People appears to be as high as or higher than rates reported in many other populations. Rates increased to the highest age group, consistent with populationbased studies. Further investigation is warranted to examine risk factors for PD in this remote population. C 2015 International Parkinson and Movement Disorder V Society
K e y W o r d s : Parkinson’s disease; incidence; prevalence; neurodegeneration; American Indian; Navajo; epidemiology
but incidence rates reported in the United States and Europe range from 12 to 15/100,000 for all ages to 62 to 332/100,000 (median 5 160/100,000) for ages 65 years or older.4-11 Although ethnic variation in the occurrence of PD indicates that different populations could harbor unique risk factors,8 few studies have examined rates of PD in American minority groups.6,7,9 Description of the epidemiology of PD in different populations is important, not only to define disease burden but also to contribute clues to the search for undiscovered etiologies. The Navajo Nation, with approximately 200,000 inhabitants residing on 25,000 square miles of land in northeastern Arizona, southeastern Utah, and northwestern New Mexico, is the largest reservation for American Indians in the United States.12 Health care
P A R K I N S O N ’ S
is provided for Navajo People through a combination of tribal and federal health care facilities, with the latter managed by the Indian Health Service (IHS).13 Disease rates, risk factors, quality of care, and response to therapies for neurological conditions in the Navajo Nation are, with few exceptions, unexplored.14 Greater appreciation of neurological illnesses could lead to fairer allocation of resources, ensure high quality of care, and open new approaches to disease prevention. The goal of this study was to give a comprehensive description of the epidemiology of PD among Navajo People residing in the Navajo Nation.
Methods The IHS, an agency of the United States Department of Health and Human Services, provides health care to members of federally recognized American Indian and Alaska Native tribes throughout the continental United States and Alaska, including American Indians residing in the Navajo Nation.13 The IHS Navajo Administrative Area partitions the Navajo Nation into eight Service Units for health care13; five are operated by the IHS and three by the Navajo government. Data for Navajo People who received care directly from the IHS or tribal health care facilities or who were referred for contract health services were obtained from the IHS National Patient Information Reporting System. These data include all hospital discharge and outpatient visit records from IHS- and tribally-operated medical facilities in the Navajo Nation, as well as facilities and providers that contract to provide healthcare services.15,16 We determined the average annual incidence and point prevalence rates of PD among Navajo People receiving health care for the calendar years 2001 through 2011. The unit of analysis for this study was the patient. Data for electronic inpatient and outpatient visit records with the International Classification of Diseases, 9th Revision, Clinical Modification (ICD9-CM) code for PD (332.0) listed as one of up to 15 diagnoses were selected for eligible people.17 Patients with PD were eligible to have their records included in the analysis if they were enrolled members of the Navajo Nation, resided in one of the eight IHS Navajo Area Service Units, and had a visit to a tribal or IHS clinical facility in the Navajo Nation. For incidence estimates, patients were required to have at least two PD-associated inpatient or outpatient visits during 2002 through 2011, with no such visits during 2001. Point prevalence estimates were calculated as of the midpoint in the study period, July 1, 2006, and included all patients with at least two PDassociated inpatient or outpatient visits during 2001 through 2011, at least one of which occurred before July 1, 2006, and who were presumed to be alive on
D I S E A S E
A M O N G
T H E
N A V A J O
July 1, 2006. A patient was considered alive if he had a visit of any kind in the IHS healthcare system between July 1, 2006 and December 31, 2011. This approach was taken because the IHS healthcare data are not linked to death certificate records, and some elderly Navajo are given traditional burials outside the usual system of documentation. Two visits were used in the case definition to reduce the impact of single coding errors.18 We used two planned methods to assess the validity of the PD case definition. After approval from the institutional review board, a movement disorders specialist (P.H.G.) conducted a chart review at the Northern Navajo Medical Center to evaluate accuracy of diagnosis and coding in a subset of cases from the Shiprock Service Unit. Modified Core Assessment Program for Intracerebral Transplantation/Hughes diagnostic criteria19-21 were used as the diagnostic standard. Specifically, we determined whether cases exhibited (1) At least two of: resting tremor, cogwheel rigidity, bradykinesia, and postural instability, at least one of which must have been either resting tremor or bradykinesia; (2) no suggestion of a cause for another Parkinsonian syndrome such as drugs, trauma, brain tumor, or treatment within the last 12 months with a dopamine-blocking or dopamine-depleting agent; and (3) no atypical features such as prominent amyotrophy, cerebellar signs, limb apraxia, oculomotor palsy, pyramidal signs, severe orthostatic hypotension, or vocal cord paresis. If data in the medical record were insufficient to assess the diagnosis, additional information was obtained from the treating physician. For the second planned assessment, the rates of other Parkinsonian syndromes were calculated to determine whether physicians and coders could discriminate between PD and drug-induced parkinsonism (ICD-9CM code 332.1) or Parkinson’s Plus syndromes (333.0).17 Patient records were examined by age group (
ARTICLE
Incidence and Prevalence of Parkinson’s Disease Among Navajo People Living in the Navajo Nation Paul H. Gordon, MD, PhD,1* Jason M. Mehal, MPH,2 Robert C. Holman, MS,2 Michael L. Bartholomew, MD,3 James E. Cheek, MD, MPH,4 and Andrew S. Rowland, PhD4 1 Indian Health Service, U.S. Department of Health and Human Services, Northern Navajo Medical Center, Shiprock, New Mexico Division of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, Georgia 3 Division of Epidemiology and Disease Prevention, Office of Public Health Support, Rockville, Maryland 4 Public Health Program, Department of Family and Community Medicine, University of New Mexico Health Sciences Center, Albuquerque
2
ABSTRACT:
Parkinson’s disease (PD) is largely unstudied among American Indians. Unique populations might harbor clues to elusive causes. We describe the incidence and prevalence of PD among Navajo people residing in the Navajo Nation, home to the largest American Indian tribe in the United States. We analyzed 2001-2011 inpatient and outpatient visit data for Navajo people obtained from the Indian Health Service, which provides health care to American Indian people living on the Navajo Reservation. Cases were defined by at least two inpatient or outpatient visits with the diagnosis of PD. Crude and age-adjusted incidence and prevalence rates were calculated overall as well as by age, sex, region of residence, and time period. Five hundred twenty-four Navajo people with median age-at-onset of 74.0 years were diagnosed with PD during the study period, yielding an average annual crude incidence rate of 22.5/100,000. Age-specific incidence was 232.0 for patients 65 years of age or older and 302.0 for 80 years
The etiologies of Parkinson disease (PD), thought to be related to complex genetic and environmental interactions,1,2 are uncertain for most patients.3 Clearer understanding is needed to accelerate the pursuit of neuroprotective therapies. Study methodology differs,
------------------------------------------------------------
*Correspondence to: Dr. Paul H. Gordon, Northern Navajo Medical Center, Medical Staff Office, Hwy 491 North, Shiprock, New Mexico 87420, E-mail: [email protected] Funding agencies: None.
Relevant conflicts of interest/financial disclosures: Nothing to report. Full financial disclosures and author roles may be found in the online version of this article. Received: 13 May 2014; Revised: 3 December 2014; Accepted: 17 December 2014 Published online 4 February 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/mds.26147
714
Movement Disorders, Vol. 30, No. 5, 2015
of age or older. Age-adjusted incidence was 35.9 overall (238.1 for 65 years), was higher in men than in women (47.5 vs. 27.7; P < 0.001), varied by region (P 5 0.03), and was similar between time periods (20022004 vs. 2009-2011). The age-adjusted point prevalence rate was 261.0. The rate of PD among Navajo People appears to be as high as or higher than rates reported in many other populations. Rates increased to the highest age group, consistent with populationbased studies. Further investigation is warranted to examine risk factors for PD in this remote population. C 2015 International Parkinson and Movement Disorder V Society
K e y W o r d s : Parkinson’s disease; incidence; prevalence; neurodegeneration; American Indian; Navajo; epidemiology
but incidence rates reported in the United States and Europe range from 12 to 15/100,000 for all ages to 62 to 332/100,000 (median 5 160/100,000) for ages 65 years or older.4-11 Although ethnic variation in the occurrence of PD indicates that different populations could harbor unique risk factors,8 few studies have examined rates of PD in American minority groups.6,7,9 Description of the epidemiology of PD in different populations is important, not only to define disease burden but also to contribute clues to the search for undiscovered etiologies. The Navajo Nation, with approximately 200,000 inhabitants residing on 25,000 square miles of land in northeastern Arizona, southeastern Utah, and northwestern New Mexico, is the largest reservation for American Indians in the United States.12 Health care
P A R K I N S O N ’ S
is provided for Navajo People through a combination of tribal and federal health care facilities, with the latter managed by the Indian Health Service (IHS).13 Disease rates, risk factors, quality of care, and response to therapies for neurological conditions in the Navajo Nation are, with few exceptions, unexplored.14 Greater appreciation of neurological illnesses could lead to fairer allocation of resources, ensure high quality of care, and open new approaches to disease prevention. The goal of this study was to give a comprehensive description of the epidemiology of PD among Navajo People residing in the Navajo Nation.
Methods The IHS, an agency of the United States Department of Health and Human Services, provides health care to members of federally recognized American Indian and Alaska Native tribes throughout the continental United States and Alaska, including American Indians residing in the Navajo Nation.13 The IHS Navajo Administrative Area partitions the Navajo Nation into eight Service Units for health care13; five are operated by the IHS and three by the Navajo government. Data for Navajo People who received care directly from the IHS or tribal health care facilities or who were referred for contract health services were obtained from the IHS National Patient Information Reporting System. These data include all hospital discharge and outpatient visit records from IHS- and tribally-operated medical facilities in the Navajo Nation, as well as facilities and providers that contract to provide healthcare services.15,16 We determined the average annual incidence and point prevalence rates of PD among Navajo People receiving health care for the calendar years 2001 through 2011. The unit of analysis for this study was the patient. Data for electronic inpatient and outpatient visit records with the International Classification of Diseases, 9th Revision, Clinical Modification (ICD9-CM) code for PD (332.0) listed as one of up to 15 diagnoses were selected for eligible people.17 Patients with PD were eligible to have their records included in the analysis if they were enrolled members of the Navajo Nation, resided in one of the eight IHS Navajo Area Service Units, and had a visit to a tribal or IHS clinical facility in the Navajo Nation. For incidence estimates, patients were required to have at least two PD-associated inpatient or outpatient visits during 2002 through 2011, with no such visits during 2001. Point prevalence estimates were calculated as of the midpoint in the study period, July 1, 2006, and included all patients with at least two PDassociated inpatient or outpatient visits during 2001 through 2011, at least one of which occurred before July 1, 2006, and who were presumed to be alive on
D I S E A S E
A M O N G
T H E
N A V A J O
July 1, 2006. A patient was considered alive if he had a visit of any kind in the IHS healthcare system between July 1, 2006 and December 31, 2011. This approach was taken because the IHS healthcare data are not linked to death certificate records, and some elderly Navajo are given traditional burials outside the usual system of documentation. Two visits were used in the case definition to reduce the impact of single coding errors.18 We used two planned methods to assess the validity of the PD case definition. After approval from the institutional review board, a movement disorders specialist (P.H.G.) conducted a chart review at the Northern Navajo Medical Center to evaluate accuracy of diagnosis and coding in a subset of cases from the Shiprock Service Unit. Modified Core Assessment Program for Intracerebral Transplantation/Hughes diagnostic criteria19-21 were used as the diagnostic standard. Specifically, we determined whether cases exhibited (1) At least two of: resting tremor, cogwheel rigidity, bradykinesia, and postural instability, at least one of which must have been either resting tremor or bradykinesia; (2) no suggestion of a cause for another Parkinsonian syndrome such as drugs, trauma, brain tumor, or treatment within the last 12 months with a dopamine-blocking or dopamine-depleting agent; and (3) no atypical features such as prominent amyotrophy, cerebellar signs, limb apraxia, oculomotor palsy, pyramidal signs, severe orthostatic hypotension, or vocal cord paresis. If data in the medical record were insufficient to assess the diagnosis, additional information was obtained from the treating physician. For the second planned assessment, the rates of other Parkinsonian syndromes were calculated to determine whether physicians and coders could discriminate between PD and drug-induced parkinsonism (ICD-9CM code 332.1) or Parkinson’s Plus syndromes (333.0).17 Patient records were examined by age group (
