In 2011, Hemming et al. assessed the racial and socioeconomic disparities (annual income and educational level) via cross-sectional analysis of patients seen at a tertiary Movement Disorders center at the University of Maryland. The authors evaluated the prevalence of PD among patients who self-identified as African-Americans compared to whites (93.4% white and 6.1% African-American).

The study revealed that African-Americans, at the time of diagnosis, had greater disability, disease severity, and were prescribed fewer anti-parkinson medications than Caucasians. Most notably, African-Americans had a two-fold increase in years between disease onset and diagnosis [2] . The limitations of this study included a small sample size (66 African-Americans) and referral bias given a select population referred to a tertiary center. Other confounding factors, such as socioeconomic status including income

and level of education. The authors stated racial disparities are multi-faceted, and recommend additional studies that assess the attitudes of patients and physicians regarding PD, PD referral and treatment.

Willis et al. assessed racial differences in PD via a cross-sectional study, which also identified potential environmental factors. In this study, PD cases were identified from the United States Medicare benefit recipients with ICD-9 codes 332 or 332.0 in 1995, and from 2000 to 2005. Benefits recipients with ICD-9 codes 332.1 (secondary Parkinsonism) or 333.0 (other degenerative disease of the basal ganglia) were excluded. The sample size was 450,000 PD cases per year. Medicare denominator files included birth, race, sex, residence, zip code, and mortality data for US Americans over the age of 65. It did not include people who were eligible for Medicare, but were in a health maintenance organization. The mean prevalence of PD was 1,588.43/100,000 among Medicare beneficiaries over age 65. Of the Medicare recipients, the mean age-related prevalence of PD was 1671.63/100,000 among Caucasian enrollees and 1,036.41/100,000 among African-American enrollees. The mean annual incidence of PD for Medicare recipients from 2002 to 2005 was 445.79/100,000 and this remained stable since 1995 [3] .

This was a well-designed study, which was well powered due to the large sample size. It also analyzed the prevalence and incidence of PD, which included demographic as well as geographic factors. Willis et al. confirmed that the prevalence among African- Americans were fifty percent lower than the prevalence among Caucasians. The incidence ratio among African-Americans as compared to Caucasians were higher than the prevalence ratio, suggesting African-Americans have a greater PD-related mortality than Caucasians. The study also reduced referral and selection bias because the cases were obtained from a database. Geographic and demographic variables were analyzed as well, which revealed a higher prevalence of PD in the Midwest and Northeast areas. The regions were termed the “Parkinson disease belt.” The limitations of this study included data collection. Obtaining Medicare files excluded patients who were less than 65 years of age. Although, the incidence of PD increases with age, the mean age of onset is 61.6 years, so patients who are not yet on Medicare were excluded [4] . The use of billing codes can result in false positives due to miscoding of other parkinsonian syndromes as PD. The risk of false negatives may be higher among African-Americans if there is a delay in diagnosing PD. Lack of access to care may exclude African-Americans from obtaining Medicare.

In another study, Dahodwala et al. reviewed Pennsylvania Medicaid claims from January 1, 1999 to December 31, 2003 to evaluate treatment disparities in PD [5] . Cases that included a claim for secondary Parkinsonism, such as schizophrenia and bipolar disorder were excluded. Three hundred seven new cases of PD were identified based on the criteria of Medicaid enrollment, having one Medicaid reimbursement claim associated with PD, and no previous claims associated with PD or Parkinsonism related disorders.

Treatment for PD included medications, physical therapy and/or a return clinic visit for PD within six months of the initial diagnosis. Of the new cases, 86% were Caucasian and 14% were African-American. There were no statistical differences in age, sex, initial diagnosis, or Medicaid eligibility between the two groups. Of the 307 cases, 104 were prescribed medication or physical therapy while 124 received a second visit. One-third of African-Americans received PD treatment compared to Caucasians (p = 0.002). There were no differences in the number of return clinic visits. This study highlights the racial disparities in treatment of PD. The authors hypothesized that lack of effective communication from providers to African-American patients with PD may have contributed to the gap in quality of care. It was also unclear, if the lower rate of treatment among African-Americans were from the providers not prescribing, or the patients not accepting treatment.

The study was limited by selection bias, as the patients with PD who applied for Medicaid were typically low income and disabled. It also lacked documentation of the clinical reasoning or decision making that may have contributed to African-Americans not receiving treatments, such as comorbid conditions that make treatment difficult [5] . The authors recommended interventions to address disparity, such as community, patient and physician awareness, as well as developing interventions to reduce inequities in care. However, these were not discussed in detail.

Cheng et al. analyzed disparities of care among veterans with PD in a retrospective study using ICD-9 code 332.0 from October 1, 2001 to September 30, 2002 followed by further chart review of the same patients, from 1998 to 2004. Medical charts were reviewed by trained nurses blinded to the study hypothesis to confirm the diagnosis of PD using ten indicator measures of PD care [6] . Out of five hundred seventy-seven cases with ICD-9 code 332.0, four hundred one PD cases were confirmed. Of those cases, twenty-seven were excluded due to lack of information about race or ethnicity. Results showed that physicians were more likely to confirm a diagnosis of PD among Non-Hispanic Whites than non-Whites. Physicians assessed depression equally among non-Hispanic whites and non-Whites, but the non-Hispanic whites were more likely to start treatment and receive follow-up. Patients who were offered treatment for depression and refused were included in the initial treatment group. Many providers did not document if they offered treatment for depression among the untreated group.

Dahodwala et al., Cheng et al., and Chan et al. highlighted several ways race affects access to healthcare and treatment. Each of the studies revealed that even after being diagnosed with PD, African-American patients did not receive adequate first line medications, physical therapy, treatment for depression, or referral for deep brain stimulation (DBS) procedure [5] [6] [7] .

African-Americans were found to have significantly fewer DBS procedures compared to Whites (unadjusted odds ratio, 0.13; 95% confidence interval, 0.11 - 0.16; P < 0.001) [7] . After adjusting for comorbidities that may contraindicate DBS, African-Americans were eight times less likely to receive DBS treatment. Despite the fact that African-Americans were more likely to receive care from urban hospitals with a higher number of neurologists and neurosurgeons.

The disparities in care also included treatment for Parkinson’s disease depression (PDD). Proper treatment of depression is associated with better quality of life. Cheng et al. reported that physicians did not consistently document whether PD patients who were depressed refused either medication or mental health referral. The rates of initial treatment (92% vs. 80%, p = 0.04), and follow-up treatment (82% vs 64%, p = 0.05) of depression among African-Americans were lower than non-Hispanic whites, despite there being no difference between race and ethnicity in the assessment of depression [6] .

Dahodwala et al., reported that African-Americans were four times less likely than whites to receive any PD treatment (odds ratio, 0.24; 95% confidence interval, 0.09 - 0.64), including physical therapy. This raises concern for communication breakdown among the providers [5] . They also reported a difference in expectations between the populations about normal aging.

An interesting confounding variable regarding PD epidemiology in different populations is variation in perceptions of normal aging. Dahodwala and colleagues were the first to examine this by comparing the stage of disease at which African-Americans and white PD patients were first diagnosed [8] . By comparing records from the Philadelphia Veterans Affairs Medical Center, they determined that African-American patients initially presented at more advanced stages of disease compared to their white counterparts (Hoehn and Yahr stage, 2.5 vs 2.0). Surprisingly, despite greater motor impairment, the degree of reported disability among African-Americans was half of what whites reported (Unified Parkinson Disease Rating Scale-disability, 40% vs 81%). This striking discovery regarding disease perception provides a plausible, yet likely partial, explanation for the documented discrepancies in PD prevalence between African- Americans and Caucasians.

Discrepancies in perceptions of normal motor performance with aging was explored directly again by Dahodwala and colleagues [9] . They generated a novel assessment tool for testing participants’ views on Expectations Regarding Movement (ERM) with questions tailored for parkinsonian symptoms. The investigators used this questionnaire to assess 210 senior center residents in Delaware County, Pennsylvania and demonstrated African-Americans held significantly lower expectations for maintenance of mobility compared to whites. However, there was no difference between the groups with respect to expectations of aging in general. Other participant characteristics that significantly improved ERM scores were higher education (more than high school) and better self- reported health (very good or excellent).

Another study investigated the issue of perceptional variation in PD with a two- pronged approach in senior communities in Philadelphia [10] . The study first held focus groups in senior centers to obtain a qualitative understanding of differences in knowledge and perspectives on PD amongst whites, African-Americans and Chinese- Americans. In the quantitative arm of the study, Pan and colleagues constructed a questionnaire based on the findings from the 75 focus group participants. The questionnaire was administered to 154 individuals and revealed commonalities and differences between the three racial groups. Two common themes shared across groups were an overall lack of knowledge regarding the disease, and concern over losing independence as a consequence of developing PD. Distrust of the healthcare system and language barriers were identified as unique obstacles to treatment perceived by African- and Chinese-Americans. Echoing previous studies, African- and Chinese-Americans were both more likely to view parkinsonian symptoms as part of normal aging compared to whites.

These three illustrative studies revealed substantial differences in both expectations for normal aging and perceived degree of disability from parkinsonian symptoms. The work highlights a likely contributing factor in the variance in PD prevalence amongst different racial and ethnic groups. These studies also point to the importance and need for outreach and education regarding PD in the senior population.