The relationship between platelet distribution width and disease activity in patients with polymyositis

Muscle enzymes are an indicator of ongoing muscle damage and disease activity in patients with idiopathic inflammatory myopathy. Although platelet-related parameters have been shown to be useful as markers of disease activity in autoimmune diseases, the relationship between platelet distribution width (PDW) and disease activity has not been previously studied in polymyositis. We aimed to determine the relationship between PDW and disease activity in patients with polymyositis.

Twenty-seven patients with polymyositis and thirty healthy controls were included in the study. Disease activity was evaluated using the myositis disease activity assessment Visual Analogue Scale (MYOACT) and the Myositis Intention to Treat Index (MITAX). The relationship between PDW and disease activity was evaluated using Pearson's or Spearman's correlation and reliability was assessed using correlation coefficients.

The mean platelet volume (MPV) and plateletcrit (PCT) were significantly higher and PDW was significantly lower in patients with polymyositis compared to the control group. The mean PDW levels were lower in patients with constitutional symptoms and arthralgia/arthritis (p < 0.005). Although PDW levels were lower in patients with mechanical hand, lung involvement, or dysphagia compared to patients without, there was no statistically significant difference between them. Platelet distribution width was found to be negatively correlated with disease activity.

We found that PDW was negatively correlated with MYOACT and MITAX, widely used tools in assessing the disease activity of polymyositis. Based on this, PDW may be utilized as a non-invasive potential index to assess disease activity in patients with polymyositis.