Recent sunburn was associated with the development of dermatomyositis (DM), data from a U.S. national patient registry suggested.
Compared with patients diagnosed with other forms of myositis, those who reported having had two or more sunburns in the previous year had almost twice the risk of developing DM (odds ratio 1.77, 95% CI 1.28-2.43, P=0.0005), according to Lisa G. Rider, MD, of the National Institute of Environmental Health Sciences' Environmental Autoimmunity Group in Bethesda, Maryland, and colleagues.
And even having one sunburn in the year prior to diagnosis was significantly associated with the diagnosis of DM versus the other types of myositis, with an OR of 1.44 (95% CI 1.06-1.95, P=0.018), they reported online in Arthritis Care & Research.
Those analyses compared DM patients with those having polymyositis or inclusion body myositis, and the analyses were adjusted for age at diagnosis, sex, and skin tone.
The three phenotypic variants of myositis are all characterized by muscle weakness, inflammation, and genetic risk factors, but in DM there also are photosensitive rashes and autoantibodies such as anti-Mi-2 and transcription intermediary factor 1 gamma.
Previous studies have identified higher rates of DM versus polymyositis in areas of the country with greater levels of ultraviolet (UV) radiation, and some evidence exists that DM patients with frequent photosensitive rashes are more sensitive to UV exposures. However, individual-level data on DM risk and UV exposure have been sparse.
Rider and colleagues recruited 1,350 patients enrolled in the MYOVISION registry, including 638 with DM, 422 with polymyositis, and 290 with inclusion body myositis diagnosed since 1990. Participants completed questionnaires detailing demographics, residence, sun exposures related to occupation and/or recreation, skin tone and sensitivity, and number of sunburns in the previous year.
Individual UVB radiation exposure was estimated using data from the Total Ozone Mapping Spectrometer according to U.S. Postal Service ZIP codes.
In the DM group, 264 reported one or more sunburn in the previous year and 368 reported none; in the combined group of patients with polymyositis or inclusion body myositis the corresponding numbers were 200 and 511. Median ages ranged from 44 to 54. More than 80% of DM patients were women, as were 60% of the combined group of polymyositis or inclusion body myositis patients.
High or moderate recreational sun exposure was reported by 67% of the DM patients compared with 61% of the polymyositis/inclusion body myositis group (OR 1.34, 95% CI 1.05-1.73, P=0.021), whereas a significant association was not seen between DM and high or moderate occupational exposure. Sun exposure from occupational plus recreational causes was significantly associated with DM for those reporting high or moderate levels of exposure (OR 1.64, 95% CI 1.08-2.49, P=0.020).
In addition, patients living in areas where the ambient UV radiation level was above the median maximum daily dose and who had high or moderate sun exposure had a statistically significant increased likelihood of developing DM (OR 1.89, 95% CI 1.03-3.48, P=0.040).
Analyses also revealed differences according to sex. For example, women had a stronger association for sunburns and DM, with an OR of 1.98 (95% CI 1.36-2.89) for two or more sunburns in the past year. In contrast, occupational sun exposure had a stronger association with DM for men, with an OR of 1.70 (95% CI 1-2.90) for high or moderate levels of exposure.
Previous studies have observed sex differences in the incidence of sunburn and sun-protective behaviors, but there has been increasing evidence that these differences also relate to immune-related effects of UV radiation. White men have been reported as having higher levels of sensitivity to UV-related immunosuppression, and an animal model of melanoma demonstrated a greater response to lower levels of UV. "A larger sample is needed to disentangle sex differences in sun exposure from differences in responsiveness to ambient UV," the researchers wrote.
There also has long been interest in a potential role -- positive or negative -- for UV radiation in various types of autoimmune diseases. It has been suggested as having a protective role in rheumatoid arthritis and multiple sclerosis, but has been implicated as a risk factor for systemic lupus erythematosus. Moreover, "there are multiple mechanisms that may contribute to acute effects of intense UV exposure on the development of an autoimmune response, including increased reactive oxidative species, damage to DNA, and apoptosis leading to cellular debris and other changes," Rider's group explained.
"Our findings support the hypothesis that UV exposure modulates idiopathic inflammatory myopathy phenotype and influences the risk of developing DM, and they provide evidence that individual-level factors related to personal sun exposure are associated with the probability of developing DM compared to other myositis phenotypes," the authors observed.
Study limitations included its retrospective design and a lack of information on the use of photoprotective measures.
Disclosures
The study was funded by the NIH Intramural Research Program, the National Institute of Environmental Health Sciences, the Myositis Association, and the Centers for Disease Control and Prevention.
Rider and co-authors disclosed no relevant relationships with industry.
Primary Source
Arthritis Care & Research
Source Reference: Parks C, et al "Association of ultraviolet radiation exposure with dermatomyositis in a national myositis patient registry" Arthritis Care Res 2019; DOI: 10.1002/acr.24059.