High Prevalence of Rheumatoid Arthritis in Yakima Indians

R. Palmer Beasley. Robert F. Willkens. and Peter H. Bennett

A survey among Yakima Indian women, ages 18 to 79, in central Washing- ton State revealed a prevatence of definite rheumatoid arthritis of 3.4%. compared with 1.4% among American women in the National Health Examination Survey (NHES). The prevalence is higher than has been ob- served in any previously studied population. Men were not studied. The prevalence was high in all age groups, but was most excessive among women under age 35.

Comparison of populations with differing r a t a of a disease have often provided important leads in the understanding of the etiology. Strik- ing differences in prevalence in different popu- lations are characteristic of most diseases. It is therefore noteworthy that the prevalence of rheumatoid arthritis (RA) has been quite sim- ilar in the numerous and divergent populations in which it has been studied (1-20). This sur- vey was undertaken to estimate the prevalence of RA among Yakima Indians, because physi- cians caring for them believed the disease was unusually Common. The survey included an agc-stratified random sample of women from 18 to 79 years of age living on their reservation

Fmm the Department of Epidemioloqy and International Health, School of Public Health and Community Medicine. and Depanment of %fedicine, School of Medicine, Univcr- rity of Washington. Seattk. Washinqton; and Southwestern Fidd Studies Smion, National Institute of Arthritis. Me- tabolism and Digestive Diseases, National Institutes of Hdth, Phoenix. ki iona.

Supported in part by grants from the Health Services and M a u l Health Administration, the Graduate School Re- search Fund of the University of Washington, and a private donation. L PAWER BEASLEY. m: Associate Professor, Depart-

mnt d Epidcmiolog). and International Health, Univer- rity d Washington, Seattle. Washinqton; ROBERT F. WIU- .LWI. IOD: Clinical Profeuor, Department of Medicine, Unirrrrity of Washingon; PETER H. BeNNt-rr, MD: Visiting hociate, Clinical Field Studies Unit, National Institute of Arthritis and Metabolic Diseases.

Rcprinc requests should be addressed to: Division of Arrbritb, Universitvof Washingon, Seattle. WA98105.

Submitted for publication April 25. 1973; accepted July 3.1973.

in central Washington State. Men were not included because they were too difficult to contact.

MATERIALS AND METHODS Sample Selection

The Yakima Tribe is composed of 5665 persons. many of whom live on a reservation occupyinq 1875 square miles in central Washington State. Indians who are 25% or more pure Yakima are enrolled in the tribe shortly after birth. Once enrolled, there are no further requirements for main- tenance of enrollment. It is senerallv believed that few eli- gible Indians fail to enroll. because it is the only basis of eli- gibility for the rights and privileqes of tribal membership: the most important of which is the distribution of tribal wealth. Tribal income is distributed twice yearly on a pcr capita basis to enrollees irrespective of aqe or sex.

An unknown number of other persons also live on the reservation. T h e x include Indians who are culturally Ypkima but have less than 25% Yakima blood required for mrollment, Indians from other tribes, and some non- Indians. The survey sample was randomlv selected from an age-stratified list of the 1731 enrolled Yakima women be- tween .I8 and 79 yean of age living on the reservatiom The age strata were arbitrarily chosen to be 18 to 34. 33 to 54. and 55 to 79. The sample size for each of these qroups was 185,223. and 93 respectively. for a total sample of 501.*

Diagnostic Criteria Almost all previous population studies of RA have used

the criteria b a d on those of the American Rheumatism As-

‘For the two older groups the u and B levels were both set at .05 for the hypothesis that Yakima women had a threefold increase of RA over the NHES prevalence for the same age group. For the younqest group a and B were r t at 0.20 for the hypothesis of a tenfold increase over the NHES.

Arthrltir and Rheumatism, Vol. 16, No. 6 (November-December 1973) 743

BEASLEY ET AL

Table 1. Distribution of Rheumato id Arthritis (RA) Cases Among Yakima Indian Women Compand With the National Health Examinat ion Survey

~ ~~~

National Health Yakima Indian females Examination

Number in Prevalence of RA Prevalence of RA survey N u m b e r s e e n N u m b e r with RA (%I (%I

18-34 185 163(88.1%) 6 3.2. 0.06 35-54 223 209 (93.7%) 6 2.7 1 .o 55-79 93 93 (100%) 5 5.4 3.6

TOTAL 501 465 (92.8%) 17 3.4t 1.4

*P< .oooo5. trc .001.

sociation (ARA). B e c a w we were operating under an hy- pothesis that RA was unusually frequent among Yakimrt Indians. we intentionally chose diagnostic criteria that were more rigid than have k e n used in other prevalence sur- veys. All persons identified as havinq RA in this report met the .ARA criteria (CIOMS-Rome) for definite or classical disease (5 or more points) (5) and at least t h m of the four New York criteria fnr RA (criteria 1 and 2 plus either 3 or 4) (21). The New York criteria require 1) a his- tory of plyarthritis 2) physical findinqs (swelling. sublux- ation. limitation of motion or ankylosis in at least 3 limb joints, includinq 1 symmetrical pair and at least 1 hand or foot). and 3) radioloqic evidence of RA and/or 4) the p m - cncc of rheumatoid factor in the serum. Thcx criteria re- quired more were. extensive. and chronic physical find- ings than do the A R h criteria and require also a history of polyarthritis. Serolo~ic and radiologic criteria are un- changed from the ARA criteria, but they are given more relative weight.

All cases of RA described in this study also had unquivo- cal clinical RA, which at the minimum meant chronic sym- metrical deformities of the hands andior wrists. Pennns about whom there was diaqnostic doubt to either examiner (RPB or RFW) were not included wen if they technically fulfilled the ARA and New York criteria. Patients with acute plyarthritis without chronic chanqa were not in- cluded. Throushout this papcr the designation, “definite rheumatoid arthritis.” when rcfcrrinq to the ARA criteria will mean “definite“ plus “classical” in their classification.

Survey Techniques Because of limited available ~esources, it was impractical

to obtain detailed historical, physical examination, and ra- diologic data from wcry suhjert in the sample. Each woman on the survcv was initially screened by a medical student es- pecially trained for the purpose. The history and physical examination w a recorded on a standard form and a blood

sample r q u a t e d . Women havinq findinqs suqqcstivc of RA were referred to two of us (RPB and RFW) for evaluation. Persons whom either examiner considered to have RA had hand x-ravs and were referred to the other examiner for confirmation. While some patients were waluated in the USPHS Indian Health Clinic. many who were unable or unwilling to come to the clink were s e n in their homes. Be- c a u x medical students were used to scrcen patients we did not attempt to assess the frqucnry of probable 3r possible RA. Medical students were able to quickly learn the fea- tures that characterized the severe rases that were inrluded by our diagnostic criteria. The qreater diagnostic subtlety for cases of lesser swerity. howwcr. would have required a professional examination for most persons with joint mom- plaints. and while desirable. this would have been beyond our resources.

Serology and X-Ray Sera were fated for rheumatoid factor by the bentonite

flocculation test (BFT) (22). T h e sera from persons who were suspected of hrlvinq rheumatoid arthritis were also tested bv the shcep cell agglutination (SCt\T) method (23). The sera were considered positive when thcv rearred at a di- lution of 1 :32 or qreatcr by either method. X-rays were read blind by the methods and standards of Kellqrcn and Law- rence (24.25).

RESULTS A total of 465 of the 501 women (93%) from

the sample were evaluated. Among these. 17 cases of RA meeting the rigid criteria of this study were identified, a prevalence of 3.4%. Table 1 shows the prevalence by age and com- pares the k’akima rates with those of the h’a-

744 Arthritis and Rheumatism, Vol. 16. No. 6 (Nowmber-December 19m)

RA IN YAKIMA INDIANS

trbk 2 Rheumatoid Arthritis Cares Among Yakima Indians

Physical exam Serology* Age

Case Age at onset Joint scoret Nodules EFT SCAT X-ray stage Comment

DB LA MS MP AH MS MS TS Rv DG U vo Do RI AS VD LD

24 30 31 31 34 34 38 43 43 48 50 52 55 64 67 72 76

15 26 18 24 24 23 27 38 42 42 18 47 34 50 52 29 50

17 18 25 9 9

25 11 15 15 16 14 14 25 16 18 25 25

512 1024

X 1024 X 512

64 4096

128 X 2048

1024 4096

16 X 256

128 neg 64

X 256 X 2048

512 1024

2048 64

32 2048 1024 4096

32 2048

8 nee 32

512 1024

4 4 4 Bedridden 1 1 4 Uses crutches 4 4 1 1 4 4 4 4 4 4 Bedridden 4

*Reciprocal of titer. -cored according to recommendations made at the Third International Symposium-New York. 1966

(21). Maximum score is 25.

tional Health Examination Survey since this study provides the best estimate of the preva- lence of RA in the general United States popu- lation. The overall prevalence for definite R.4 for women in the National Health Examina- tion Survey was 1.4% (5). The Yakima rates for all ages exceed those of the National Health Examination Survey. The difference is most striking for women of ages 18 to 34 whose rate of 3.2% is 50 times that of women in the same age group in the Sational Health Exami- nation Survey (P c .00005). The differences for older women between the Yakimas and the Na- tional Health Examination-Survey are not statistical 1 y significant .

Details on each of the cases are shown in Table 2. As can be seen, 16 of the 17 RX cases had a positive BFT or SCAT test, compared with only 3% (10 of 334) of those not classified as having RA. Hand x-rays showed Grade 4 changes in 13 of the 17 patients. Four others had only minimal x-ray changes.

DISCUSSION The survey estimate of the overall preva-

lence of chronic deforming RA among reserva- tion women of the Yakima Indian tribe is 3.4ri. This is in excess of prevalence rates for definite RA by the ARA criteria reported for women in any other population previously studied. Be- cause of some differences in the aye groups in- cluded in different studies, it is difficult to com- pare total prevalence rates from one popula- tion to another. It would appear, however. that the prevalence of definite RA ranges between 0.4% and 1.4% in previously studied adult fe- male populations. It is noteworthy that there appears to be less variation'in the prevalence of definite RA than probable plus definite rheumatoid arthritis, the latter being the figure most frequently quoted.

We believe these figures demonstrate that RA is unusually frequent among Yakima In- dian women. It is likely, however, that these fig- ures underestimate the real differences between

BEASLEY ET AL

Table 3. Comparison of Rheumatoid Arthritis Prevalence Among American Indian and NHES Females

Age NHES Haida Blackfeet Pima Yakima

30-34 1/373-0.3% 0/14-05 Q/62-0°0 0/83-08 5/48-10.4% 35-54 15/1489--1.03 2/58-3.4% 4/269-1.5% 4/242-1.7"0 6/223-2.7% 55 + 31/812-3.g'% O/42-Ouo 2/166-1.2u~- 8/161-5.0% 5/93-5.40b TOTAL 47/2674--1.8w0 211 14-1.8'% 6/497--1.2% 12/486-2.5% 16/364-4.4%

*.LIP: Women under age 30 are'not included in this table because data on these younger women were not available for the Blackfeet and Pima studies.

Yakimas and other populations because the cri- teria we used are more rigid than those used in all other studies. Our patients met not only the generally used AR.A criteria, but also the New York criteria and our clinical impression. Two young women who met the ARA criteria for definite RA were excluded as clinically they have ankylosing spondylitis. A number of other patients also filled the criteria but were clini- cally classified as having osteoanhritis. Other patients who met the ARA criteria and whom we believe have rheumatoid arthritis were ex- cluded by the New k'ork criteria. usually be- cause they did not have symmetrical changes in the hands or wrists. In the only population study comparing the ARA and New York cri- teria, Cathcan and O'Sullivan showed that only 40% of the patients who had definite RX by the AR.4 criteria also qualified by the New York criteria (3, 11).

Although the prevalence of RA among Yaki- ma women exceeds that-of other populations in all age groups, the excess is most striking among women under 35 years of age. Because RA is generally so infrequent among youn5er women, no single population study has been large enough to provide a good estimate of the prevalence among women under age 35. The National Health Examination Survey found only one case among 1280 women studied. Combining the figures frgm all published studies which give both the number of cases and population size. by age and sex, only 13 cases of definite RA among more than 12,000 women under age 33 have been found. This

combined rate is 0.1%, compared with 3.2% among Yakima women in the same age group in our survey.

The prevalence of rheumatoid arthritis has been studied in several other populations of North American natives. The prevalence of R.4 among Blackfeet Indians in Montana (10). Haida Indians on Queen Charlotte Island. British Columbia (4). and Eskimos in Northern Alaska (2) is not unusual. Although the latter two studies were from small populations, a study by one of us (26) has recently confirmed the absence of an unusual prevalence among Alaskan Eskimos. The prevalence of RA in k'akima women is significantly higher (P c 0.01) than it is in any of these groups. A com- parison of these rates plus those of the Na- tional Health Examination Survey and those of the Pima Indians in Arizona is shown in Table 3. This table compares prevalence rates for women over 29 years of age because two of the studies were limited to women over this age. The prevalence of R.4 among Pima women is higher than that of the Eskimos. Haidas. or Blackfeet. but lower than that of the Yakimas. The difference between the Pimas and each of these qroups is not statistically significant. It should be noted. however. that the Pimas do not have an excess in cases amonq young women a s do the Yakimas. We believe the available data is insufficient to rule out the possibility that American Indians are generally more fre- quently affected by rheumatoid arthritis than other peoples. LVe have preliminary informa- tion suggesting that other tribes in the nonh-

746 Arthritis and Rheumatism. Vol. 16. No. 6 (November-December 1973)

RA IN YAKIMA INDIANS

western United States also have an increased prevalence. We do not, however. know whether the phenomena is limited to Indians of the northwest. No prevalence studies of R.\ have yet been conducted among non-Indian popula- tions in this area. We believe that comparison of the Yakima Indians with other populations thritis 10:163-179, 1967 with lower rates of RA may identify factors which areetiologic in this disease.

9. Mikkelsen WM, Dodge HJ, Duff IF. et al: Esti- mates of the prevalence of rheumatic diseases in the population of Tecumeh. Michigan, 1959- 60. J Chronic Dis 20:331-369* 1967

10. O’Brien WM, Bennett PH, Burch T.4. et al: X genetic study of rheumatoid arthritis and rheu- matoid factor in Blackfeet and Pima Indians. Ar-

11. ~ ‘ ~ ~ l l i ~ ~ ~ JB, Cathcan ES:The prmalence of rheumatoid.mliritis. Ann .Intern &fed 76:573-

ACKNOWLEDGMENTS These studies were performed in cooperation with the

Yakima Indian Tribal Cnuncil and the Indian Health .Sew- ice of the United States Public Health Service. The authon would like to acknowledge Dr. William

Simmons, previously the Service Unit Director of the Yak- ima Indian Clinic, for havinq recoqnized the problem and for his support of the study; Mr. Richard Blandau. Mr. Fderick Hayden. Mr. Robert Nadleberq, Mr. Peter Shcrri, and Miss Patience White. medical students who gave excellent field assistance, and many persons in the In- dirn Health Service and Yakima Indian tribes for their help and cooperation.

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Arthritis and Rheumatism, Vol. 16, No. 6 (November-December 1973) 747

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748 Arthritis and Rheumatism. Vol. 16, No. 6 (Norember-December 1973)