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Dermatomyositis Incidence Rates Remain Steady Among VA Health Care Patients

Despite worldwide trend data, incidence trends for dermatomyositis do not show increases among the study population.

A research letter finds that dermatomyositis (DM) rates are not increasing and remain relatively stable among the population of US Department of Veterans Affairs (VA) health care patients.

The inflammatory condition’s rate in the US was reported as between 0.1 and 1.8 cases per 100,000 person-years, according to the research team led by Jamie L.W. Rhoads, MD, MS, and Caitlin M. Bolender, MD, of the University of Utah School of Medicine’s Department of Dermatology.

“It is challenging to evaluate the incidence trend for a rare disease, such as DM, particularly in the US, given the lack of a unified medical record system,” Rhoads and colleagues wrote. Consequently, the researchers analyzed the rates among VA patients with the condition.

Background and Research

The investigators used a retrospective cohort study of 679 veterans with DM diagnoses being treated through the outpatient VA health system from the beginning of 2005 to the end of 2019. DM incidence rates were calculated by dividing the amount of new DM cases by the number of veterans in outpatient settings within the time duration.

If DM patients’ data were used in the study, they had to have 2 DM codes from the International Classification of Diseases, Ninth Revision (ICD-9) either from a rheumatology outpatient meeting or from VA dermatology. Patients without a VA health care meeting in the year before their diagnosis were not included.

A Poisson regression was used by the investigators to analyze incidence rate trends over time among the sample population. Study results were decided to be statistically significant at P < .05 among the research team.

Study Findings

The investigators’ cohort of 679 patients with reported DM incidence cases was about 82% male, with a median age of 60 years. They also found that there was a greater percentage of females (17.5%) and White patients (68.2%) than that of the general VA outpatient population (12.8% and 63.5%, respectively).

They also found that DM cases were most frequently diagnosed between the patient ages of 50 and 69 years. During the study period, the researchers’ analysis showed a substantial downward trend in DM incidence overall (95% CI, −0.034 to −0.004; P = .01), with a slight upward trend observed among females that was deemed statistically insignificant (95% CI, −0.027 to 0.089; P = .29).

“All studies demonstrate an increasing incidence, but 1 study from Southern Australia showed that inclusion body myositis was associated with the apparent increase in idiopathic inflammatory myopathies,” they wrote. “Our study suggests that DM incidence is not increasing among the VA population.”

Despite the older and predominantly male demographics of the VA population being a limitation for the study of the overall US population, mean yearly incidence of DM when adjusted for age and sex was noted by the investigators as similar to prior studies.

The research letter, “Incidence of Dermatomyositis in a Nationwide Cohort Study of US Veterans,” was published online on JAMA Dermatology.