Is rheumatoid arthritis disappearing?

11/08/06: T Uhlig and T K Kvien, Department of Rheumatology, Diakonhjemmet Hospital, N-0319 Oslo, Norway

Is rheumatoid arthritis disappearing?

Abstract

During the past decades a number of studies have examined the occurrence of rheumatoid arthritis (RA) in different geographical settings and at different times. Studies reported a higher incidence of RA several decades ago than seen during recent years. Thus it is of interest whether there is a real decline of RA.

Introduction

There has been interest about the occurrence of rheumatoid arthritis (RA) in different geographic areas and whether there have been changes over time. Recent studies on the incidence (number of new cases) of RA have rather consistently demonstrated around 25–50 new cases annually per 100 000 population at risk. Some studies found higher incidences of RA several decades ago than seen during recent years. Thus, it is reasonable to ask whether there is a true decline in the incidence of RA.

At least three explanations are possible for changes in the occurrence of RA over time:

• The methods for diagnosis of RA vary across different studies
• There may be real geographical or ethnic differences in disease occurrence
• There may be an effect of time with a decrease in the occurrence of RA.

Methods to examine a population for RA

There are different ways to examine a population for new cases of RA:

1.Repeated Surveys

2. Recording in a population

3. Prospective notification

1. Repeated surveys were for example used in biennial examinations of  Indians in Arizona/USA. In Hiroshima and Nagasaki survivors underwent biennial examinations after the Second World War.   

2. A second technique examines case records in a fixed area. The Oslo RA register was established by identifying patients with a residential address in a well defined geographic area by retrospective record review in the two rheumatology departments in the county. The register has been shown to be complete for 85% of all RA patients. In the city of Oslo each year about 100 new individuals are identifies with having RA, giving an incidence of 25/100.00 population at risk. In another setting, citizens in Rochester, USA, who were mainly treated at the Mayo clinic, were reviewed, thus examining a whole population for the occurrence of RA.

3. Prospective notification is in many ways the ideal approach. In Seattle, Washington, patients who were members of health maintenance organisations were identified if they had RA, and study personnel were contacted by rheumatologists, internists, and family physicians. The Norfolk Arthritis Register in the United Kingdom is based on prospective notification. General practitioners are asked to notify to the register all patients with inflammatory polyarthritis within a population of almost ½ million. For patients with disease onset between 1990 and 1991 the incidence was found to be 36/100 000 in women and 14/100 000 in men, which is the same as the findings in the Oslo RA register.

All these different methods for assessment of incident RA cases have advantages and limitations that may influence the results. The numbers for incidence greatly depend on the criteria used for case definition, the definition of time of onset, and on the possible delay before seeking medical help or referral. Another approach to study the occurrence of RA is by means of self-reported diagnoses, but this has been shown to be clearly unreliable.

Early and aggressive treatment of RA has been supported during recent years. Such a practice may result in treatment even before patients have an established diagnosis. Some patients will thus not fulfil criteria that are related to disease activity and severity and may never be classified with RA.

Changes in incidence of RA might be due to a changing perception of RA and differential diagnoses by the classifying doctor. In two recent studies only about one out of seven patients in Kuopio, Finland, and one of four patients in southern Sweden presenting with inflammatory arthritis had RA according to the criteria for RA established in 1987.

Decline in occurrence of RA

A review of all studies makes it apparent that American Indians have a clearly higher incidence of RA than other populations in North America and Europe. Looking at incidence numbers from the different studies clearly suggest a secular decline of RA incidence during the 1970s. The curve then flattens out during the 1980s without consistent further decline.

Repeated studies within the same geographic regions also support that the incidence of RA is declining, and this trend was more marked in women. The most reasonable explanation for the decline of RA in women may be exposure to the contraceptive pill. In Pima Indians over a 25-year period a fall in the incidence of RA has been clearly demonstrated.

Occurrence and disease severity

Many rheumatologists in their daily work find that patients attending rheumatology clinics today have, in general, less severe disease than 20–30 years ago. For healthcare planning it would be important to know if there is a real decline in the burden of the disease for both the individual person and for society. Such information is rare, but in the Oslo RA register only

half of all patients had a disability level associated with reduced life expectancy. If managed in a setting offering comprehensive and aggressive treatment, 30–40% of these patients will develop clinically important disability due to RA within the first 3–5 years. About half of the patients also had reached clinically important levels of health status for psychosocial measures.

Summary

Present knowledge suggests that RA today occurs less often than reported several decades ago and that the incidence of RA today is lower than during the 1950s. This decline seems mainly to have occurred during the 1970s or early 1980s.

Changing methods in verifying new patients with RA may be an equally important explanation besides a real time dependent decline of RA. RA only represents a fraction of cases with inflammatory arthritis that occur. For the future it will also be important to healthcare planners to identify the proportion of patients with RA who will reach clinical levels of health requiring various health services.