Previous studies on pathogenic mechanisms indicate that the microvessels have a role in the disease mechanisms in polymyositis (PM) and dermatomyositis (DM). A reduced number of capillaries has been reported and this observation together with the increased expression of interleukin-1 and TGF-β suggest that there might be an hypoxic condition in the inflamed muscle tissue that could explain some of the clinical symptoms.
Aim of study
To further test this hypothesis we investigated if vascular endothelial growth factor (VEGF), which is upregulated by hypoxia, is expressed in muscle tissue in patients with PM and DM. A second aim was to investigate whether VEGF expression is affected by corticosteroid therapy.
Patients and methods
Six patients with PM and 4 with DM were investigated. A first muscle biopsy was taken at diagnosis and a second after 3–6 months with corticosteroid therapy. VEGF expression was investigated by immunohistochemistry using a rabbit polyclonal IgG antibody. Both conventional microscopic evaluation and computerised image analysis were used for evaluation of VEGF expression.
These are our preliminary data: First biopsy: with conventional microscopic evaluation VEGF expression was observed in the endothelial cells of the microvessels in 9/10 patients and in larger vessels such as arterioles and venules in all patients. VEGF was also expressed in muscle fibres in all, and in mononuclear inflammatory cells in 3/10 patients. In the second biopsy, VEGF expression was still present in endothelial cells of capillaries and larger vessels as well as in muscle fibres, but with a seemingly weaker expression in the endothelial cells of PM patients and an increased expression in the DM patients. With computerised image analysis the results were similar.
VEGF is expressed in endothelial cells of capillaries and slightly larger vessels, in muscle fibres, and in occasional inflammatory cells in muscle tissue from patients with poly- and dermatomyositis. After corticosteroid therapy the expression decreased in some patients and increased in other patients. Whether or not the changed VEGF expression has any clinical significance and correlates with changes in muscle function still needs to be analysed.