Clinicopathological features of graft versus host disease‐associated myositis

Abstract Background and Objective Chronic graft versus host disease (GVHD)‐associated myositis targeting skeletal muscle is a relatively rare but potentially debilitating complication following allogeneic hematopoietic stem cell transplantation (HSCT). We reviewed the clinicopathological features of GVHD‐associated myositis among patients receiving allogeneic HSCT to elucidate the cellular pathogenesis. Methods We retrospectively reviewed clinical data and muscle biopsy results from 17 consecutive patients diagnosed with GVHD‐associated myositis at our institution between 1995 and 2019. Immunostaining findings of GVHD‐associated myositis were compared to those of patients with anti‐tRNA‐synthetase antibody‐associated myopathy (ASM) (n = 13) and dermatomyositis (DM) (n = 12). Results The majority of patients with GVHD‐associated myositis showed subacute or chronic progression of mild to moderate limb weakness together with elevated serum creatine kinase. These patients also exhibited mild C‐reactive protein elevation but were negative for myositis‐related autoantibodies. Programmed death‐1 (PD‐1)‐positive cells were observed in muscle interstitium adjacent to myofibers expressing human leukocyte antigen (HLA)‐DR. The interstitium was also HLA‐DR‐positive, similar to biopsy samples from ASM patients but not DM patients. The proportions of HLA‐DR‐positive muscle fibers and PD‐1‐positive interstitial cells were significantly higher in GVHD and ASM samples than DM samples. The PD‐1‐positive cells were mostly CD‐8‐positive lymphocytes. Discussion GVHD‐associated myositis is characterized by HLA‐DR‐positive myofibers and infiltration of PD‐1‐positive lymphocytes. These features distinguish GVHD‐associated myositis from DM but not from ASM.