More than 40% of patients with systemic sclerosis show signs of myopathy
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Key takeaways:
- Proximal weakness and elevated creatine kinase were associated with a severe, inflammatory phenotype of SSc.
- Patients displaying both muscle disease biomarkers had 3.6 times higher mortality risk.
As much as 43% of patients with systemic sclerosis demonstrate evidence of myopathy, while those with proximal weakness and higher creatine kinase exhibit worse function and survival, according to data.
“We know that a lot of people living with systemic sclerosis, or scleroderma, have muscle problems,” Jessica L. Fairley, MBBS, of the University of Melbourne, in Australia, told Healio. “However, because muscle disease in SSc is heterogeneous, it has been difficult to estimate how often it occurs and the impact on individuals.”
To assess the frequency, clinical signs and impacts of muscle disease in SSc, Fairley and colleagues conducted a retrospective analysis of the Australian Scleroderma Cohort Study. The analysis included 1,786 participants who, during at least one follow-up visit, had been assessed for two possible biomarkers of SSc myopathy: elevated creatine kinase, defined as greater than or equal to 140 IU/L, and proximal weakness, defined as upper or lower limb proximal muscle power of less than 5/5.
The researchers examined data from 1,786 participants, with a mean age of 46.6 years, whom they divided into four groups based on whether they demonstrated:
- elevated creatine kinase and proximal weakness (4%);
- proximal weakness and normal creatine kinase (15%);
- elevated creatine kinase and normal proximal power (24%); or
- neither proximal weakness nor creatine kinase elevation (57%).
According to the researchers, 4% of included patients demonstrated concurrent proximal weakness and creatine kinase elevation, while 15% had proximal weakness alone, 24% had creatine kinase elevation alone, and 57% had neither.
Modeling showed that participants with both biomarkers “displayed a severe, inflammatory SSc phenotype” partly characterized by more frequent diffuse cutaneous SSc (P < .01). Proximal weakness was also associated with multimorbidity (P < .01) and cardiopulmonary disease, regardless of creatine kinase levels.
In addition, participants with both proximal weakness and creatine kinase elevation had 3.6 times the mortality risk (95% CI, 1.9-6.6) compared with those with neither, while those with only creatine kinase elevation demonstrated better survival (HR = 0.7; 95% CI, 0.4-1.1). Those with both biomarkers had the poorest physical function by multiple measures, the researchers wrote.
According to Fairley, future studies should focus on patients diagnosed with muscle disease, rather than those with “surrogate clinical indicators.” She added that “far more work is needed” to answer key questions in this area, including how to define muscle disease in SSc.
“Our findings suggest that markers of muscle disease are really common in people living with scleroderma,” Fairley said. “Furthermore, simple biomarkers of muscle disease can help identify people at risk for other, severe manifestations of scleroderma, particularly heart and lung disease. Finally, those with biomarkers of muscle disease had significantly worse survival and physical function than those without, which indicates that muscle disease is important in terms of both longevity and quality of life.”
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