NEW YORK (Reuters Health) - People with rheumatoid arthritis (RA) are at increased risk of herpes zoster, or shingles, a painful skin condition caused by a reactivation of the chickenpox virus, according to research on more than 160,000 individuals with RA.

Medications used to treat RA appear to increase vulnerability to shingles, Dr. Allison L. Smitten, from the Harvard School of Public Health, Boston, and colleagues report in the medical journal, Arthritis Care and Research.

It is "biologically plausible" that having RA may result in an increased risk of shingles due to the dysregulation of the immune system in patients with RA, they write.

By studying the US PharMetrics claims database for the period 1998-2002, which included 122,000 RA patients and one million randomly selected controls, the researchers found that the rate of shingles was significantly higher in RA patients than in controls -- 9.83 versus 3.71 per 1,000 "person-years." This translates into a 91 percent higher adjusted risk of shingles in patients with RA relative to those without RA.

A look at the UK General Practice Research Database for the period 1990-2001, which included 38,000 RA patients and 500,000 randomly selected controls, revealed rates of shingles of 10.6 per 1,000 person-years in patients with RA versus only 4.1 per 1,000 person-years, in controls - a 65 percent increased risk in the setting of RA.

Smitten and colleagues also found evidence that a variety of anti-RA drugs were associated with greater likelihood of developing shingles.

They were unable to tell if the medications themselves increased risk, or if they were simply markers for more severe disease that made patients more susceptible to reactivation of the chickenpox virus.

"Given that many of the drugs used to treat RA have been associated with substantial benefit in terms of disease improvement and quality of life, any increase in the risk of herpes zoster must be considered in the context of the benefits expected from the medications," Smitten and her associates conclude.

SOURCE: Arthritis Care and Research, December 15, 2008.