Inflammatory myopathy with abundant macrophages and dermatomyositis: two stages of one disorder or two distinct entities?

Inflammatory myopathy with abundant macrophages (IMAM) and dermatomyositis (DM) are considered to represent related disorders, since they share inflammatory infiltrates and skin alterations. In order to get more insight into these disorders, we addressed the cellular composition of the inflammatory infiltrates in muscle biopsies of 11 patients with IMAM and DM. In IMAM, inflammatory infiltrates predominantly consisted of CD68+ MRP14+ macrophages which weakly expressed TNF-α, a few CD3+ T cells with a prominent IL-10 expression, and single CD123+ plasmacytoid dendritic cells.