Arthritis Prevalence Vastly Underestimated

Diana Phillips
December 04, 2017

The prevalence of arthritis among US adults may be nearly 70% higher than current surveillance data indicate, a study has shown.

The findings suggest that the full weight of the disease burden at the population level, and its public health implications, have been greatly underestimated, S. Reza Jafarzadeh, DVM, MPVM, PhD, from Boston University School of Medicine in Massachusetts, and David T. Felson, MD, MPH, from the University of Manchester and Central Manchester NHS Foundation Trust in the United Kingdom, report in an article published online November 27 in Arthritis & Rheumatology.

The most recent national estimate of arthritis prevalence from the Centers for Disease Control and Prevention, based on 2015 National Health Information Survey data, suggests that 54.4 million adults (22.7%) in the United States are afflicted with the inflammatory condition.

However, that estimate is based on survey respondents' answer to a single question asking whether they have ever received a diagnosis of arthritis from a physician, the authors write. Yet previous reports demonstrate a low sensitivity for arthritis surveillance based only on reports of physician-diagnosed arthritis, especially among adults younger than 65 years.

Therefore, Dr Jafarzadeh and Dr Felson sought to produce a more accurate estimate by applying a more expansive surveillance definition, which included self-reported arthritis-related chronic joint symptoms.

With that approach, the 2015 National Health Information Survey data indicate that 91.2 million (36.8%) US adults, including 61.1 million between 18 and 64 years old, are affected by the condition.

Single Question Has Low Sensitivity

For their analysis, the researchers developed a Bayesian model based on an arthritis definition consistent with that suggested by the National Arthritis Data Workgroup: a clinically significant condition that is either symptomatic or requires attention from a health professional for treatment. Responses were considered positive for arthritis if they indicated physician-diagnosed arthritis; the presence of pain, aching, or stiffness around a joint, excluding the back or neck, within the preceding 30 days; and the initial onset of symptoms exceeding 3 months.

"We aimed to estimate arthritis prevalence based on an expansive surveillance definition that is also adjusted for the measurement errors in the current definition," they write.

Of 33,672 survey respondents, 15.7% of men and 13.5% of women aged 65 years or older reported joint symptoms without physician-diagnosed arthritis, as did 19.3% of men and 16.7% of women aged 18 to 64 years. The adjusted prevalence of arthritis based on the broader definition was 55.8% in men and 68.7% in women aged 65 years and older, and 29.9% in men and 31.2% in women aged 18 to 64 years, the authors report.

An assessment of the accuracy of the surveillance criteria showed low sensitivity for physician-diagnosed arthritis criterion in the 18- to 64-year age group and high sensitivity for symptom onset criterion across all age and sex stratifications, "despite having the lowest specificity," the authors write. "Thus, a substantial (i.e. 65-80%) fraction of the population with arthritis, who are between 18-64 years of age, but are misclassified as healthy by the [physician]-diagnosed arthritis criterion due to low sensitivity, are captured by the two remaining questions on joint pain, aching or stiffness."

Relying on the previously published national estimates of arthritis prevalence is problematic above and beyond the measurement errors, the authors write.

"Implicit in the question on [physician]-diagnosed arthritis, when the response is positive, is that the surveyed individual sought or had access to medical care from a health professional. However, a negative response to the [physician]-diagnosed question could be the result of either lack of medical attention to joint symptoms or a truly negative diagnosis with regard to arthritis," they explain. "Moreover, an individual who is diagnosed by a health professional to have arthritis, may never be explicitly informed of the diagnosis."

The current study was designed to better assess the burden of arthritis at the population level and does not address the diverse disease mechanisms that cause arthritis, the authors stress.

"[F]urther studies are needed to evaluate potential changes in the specific causes or arthritis, especially among adults below the age of 65," they write. "Arthritis causes an enormous economic and public health implications. Arthritis-attributable healthcare direct costs or long-term indirect costs as a result of loss of productivity and disability need be revised to account for the corrected prevalence of arthritis affecting individuals at younger age than previously perceived."

In an accompanying editorial, Jeffrey N. Katz, MD, from the Orthopedic and Arthritis Center for Outcomes Research at Brigham and Women's Hospital in Boston, Massachusetts, applauds the new study. "The work of Drs. Jafarzadeh and Felson moves our field a large step forward, both by introducing a set of techniques that permits more nuanced use of existing survey data and by highlighting the limits of the specific questions deployed at present in national prevalence surveys."

He concludes, "[T]he adjusted prevalence estimates these authors present are sufficiently robust and concerning to justify a policy agenda encouraging greater investment of scarce resources into the pathogenesis, prevention and treatment of arthritis conditions."

This study was supported by a grant from the National Institutes of Health. The authors and editorialist have disclosed no relevant financial relationships.

Arthritis Rheumatol. Published online November 27, 2017. Article abstract, Editorial extract

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SOURCE: Medscape, December 4, 2017. Arthritis Prevalence Vastly Underestimated

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