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Systemic Sclerosis: More Common than Expected

Systemic sclerosis is more common in the United Kingdom than previously reported, a nationwide population-based study determined.

Analysis of data from the Clinical Practice Research Datalink, a general practice database that includes approximately 6% of the U.K. population and is considered representative of the entire population, found an estimated overall incidence of 19.4 per million person-years (95% CI 18.3-20.4), according to Fiona A. Pearce, MBBS, and colleagues from Nottingham University reporting online in Clinical Rheumatology.

This estimate is more than four times higher than the estimate of four per million found in a study conducted in the 1980s in the West Midlands district of England, Pearce and colleagues noted.

The incidence and prevalence of SSc have been reported as having wide variations, with differences according to gender, race, and geography.

For instance, women are far more often affected, and individuals of non-European ethnicity also may have a greater risk. In addition, multiple epidemiologic studies have suggested geographic differences, including a north-south gradient in Europe, with lower rates seen in the U.K. and Finland compared with in Greece and France. One systematic review suggested higher prevalence rates for the United States (276 per million) and Australia (233 per million) than for France (158 per million) and the United Kingdom (88 per million).

"Understanding the incidence and prevalence of systemic sclerosis will help to address the healthcare needs and aid service planning for this rare disease, both now and in the future," Pearce and colleagues wrote.

Accordingly, they identified 1,327 patients in the database diagnosed from 1994 to 2013; a total of 83% were women, and mean age at diagnosis was 58.

The overall incidence of systemic sclerosis did not change during the study period.

Compared with men, women had an adjusted incidence rate ratio of 4.7 (95% CI 4.1-5.4, P<0.0001), and individuals age 55 to 69 had the highest adjusted incidence rate ratio, at 6.7 (95% CI 5.5-8.1). Unlike the situation for other autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis, socioeconomic status did not influence the incidence of systemic sclerosis.

During the study's total 6,929 years at risk, there were 302 deaths, for a mortality rate of 43.6 per 1,000 person-years (95% CI 38.9-48.8), with higher mortality rates for men and older patients. The adjusted hazard ratios for mortality were 0.7 (95% CI 0.5-1, P=0.06) for women and 37.8 (95% CI 11.6-123.2, P<0.0001) for patients ages 85 and older compared with those 16 to 39.

The 1-year, 5-year, and 10-year survival rates were 94.2%, 80%, and 65.7%, respectively.

The current estimate of new cases per year in the U.K. is 1,180, with 19,390 patients living with the disease. With a large increase in the over-55 age group expected in the next 20 years, by 2037 an estimated 1,460 new cases can be expected each year -- a 24% increase -- and 24,430 patients will be living with the disease -- a 26% increase.

"Systemic sclerosis is an important condition for rheumatologists, because although rare, it has a very high mortality compared to other musculoskeletal diseases, and optimal patient care is challenging and involves multidisciplinary effort," Pearce and colleagues observed.

They noted that although the study does not support previous findings of differences in incidence and prevalence according to geographic region, the analysis does confirm that women are more commonly affected.

A strength of the study, the team said, was the prospectively collected data, while a limitation was the relatively small number of cases. Nonetheless, "we have identified a cohort of more than 1,300 people with systemic sclerosis, which allows us to make the most precise estimates of incidence, prevalence, and survival published in a European population, which are essential for health service planning."

The authors reported having no financial conflicts of interest.

Disclosures: 
The author has no conflicts of interest to disclose related to this subject

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