Immune-mediated neuromuscular complications of graft-versus-host disease

Recent Updates on the Pathogenesis of Inflammatory Myopathies

PURPOSE OF REVIEW

This review aims to provide a comprehensive and updated overview of autoimmune myopathies, with a special focus on the latest advancements in understanding the role of autoantibodies. We will begin by examining the risk factors and triggers associated with myositis. Next, we will delve into recent research on how autoantibodies contribute to disease pathogenesis. Finally, we will explore the latest innovations in treatment strategies and their implications for our understanding of myositis pathogenesis.

RECENT FINDINGS

Recent research has revealed that myositis-specific autoantibodies can infiltrate muscle cells and disrupt the function of their target autoantigens, playing a crucial role in disease pathogenesis. Significant advances in treatment include CD19 CAR-T cell therapy, JAK-STAT inhibitors, and novel strategies targeting the type 1 interferon pathway in dermatomyositis. Additionally, the ineffectiveness of complement inhibitors in treating immune-mediated necrotizing myositis has challenged established views on disease mechanisms. Autoimmune myopathies are a collection of disorders significantly influenced by specific autoantibodies that drive disease pathogenesis. This review highlights the critical role of autoantibody research in deepening our understanding of these conditions and discusses recent therapeutic advancements targeting key pathogenic pathways.

Clinicopathological features of graft versus host disease-associated myositis

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.

Granulomatous myopathy: Sarcoidosis and beyond

Non-necrotizing granulomatous inflammation is a rare but easily recognized histopathological finding in skeletal muscle biopsy. A limited number of diseases are known to be associated with non-necrotizing granulomatous myopathy. Once identified, a careful evaluation for evidence of extramuscular granulomatosis and other signs suggestive of sarcoidosis is warranted as about half of the patients have sarcoid myopathy. In addition, the presence of granulomatous myopathy should trigger a search for clinical and pathological clues of inclusion body myositis (IBM), which accounts for most of the remaining patients and can coexist with sarcoidosis. Recognizing the features of IBM in patients with granulomatous myopathy can potentially spare the patients from unnecessary exposure to immunosuppressive therapies. In patients whose granulomatous myopathy remain unexplained, further investigations should aim at identifying myasthenia gravis and other autoimmune disorders, especially those known to cause granulomatous inflammation in other organs. Laboratory investigations should include acetylcholine receptor, antimitochondrial, antineutrophil cytoplasmic, thyroglobulin, and thyroid peroxidase autoantibodies. In the appropriate clinical context, exposure to immune checkpoint inhibitors and chronic graft-vs-host disease can be causes of granulomatous myopathy. In cases of unexplained granulomatous myopathy, natural killer/T-cell lymphoma should be considered and careful histopathological examination for atypical cells and appropriate immunostaining is crucial. Identifying the etiology of granulomatous myopathy in each patient can guide appropriate treatment.

Towards a Better Understanding of the Atypical Features of Chronic Graft-Versus-Host Disease: A Report from the 2020 National Institutes of Health Consensus Project Task Force

Alloreactive and autoimmune responses after allogeneic hematopoietic cell transplantation can occur in non-classical chronic graft-versus-host disease (chronic GVHD) tissues and organ systems or manifest in atypical ways in classical organs commonly affected by chronic GVHD. The National Institutes of Health (NIH) consensus projects were developed to improve understanding and classification of the clinical features and diagnostic criteria for chronic GVHD. While still speculative whether atypical manifestations are entirely due to chronic GVHD, these manifestations remain poorly captured by the current NIH consensus project criteria. Examples include chronic GVHD impacting the hematopoietic system as immune mediated cytopenias, endothelial dysfunction, or as atypical features in the musculoskeletal system, central and peripheral nervous system, kidneys, and serous membranes. These purported chronic GVHD features may contribute significantly to patient morbidity and mortality. Most of the atypical chronic GVHD features have received little study, particularly within multi-institutional and prospective studies, limiting our understanding of their frequency, pathogenesis, and relation to chronic GVHD. This NIH consensus project task force report provides an update on what is known and not known about the atypical manifestations of chronic GVHD, while outlining a research framework for future studies to be undertaken within the next three to seven years. We also provide provisional diagnostic criteria for each atypical manifestation, along with practical investigation strategies for clinicians managing patients with atypical chronic GVHD features.

Pathological features of inflammatory myopathy as a manifestation of chronic graft-versus-host disease after allogeneic bone marrow transplantation

Chronic graft-versus-host disease (cGVHD) is the most important complication resulting in the death of bone marrow transplantation (BMT) survivors. It is also a relatively rare cause of inflammatory myopathy (IM). We report the case of a 46-year-old woman who developed severe cGVHD-related IM after BMT for myelodysplastic syndrome. She presented with severe muscle pain and weakness with cGVHD-related symptoms in other organs. Myopathological analysis showed moderate cell infiltration with remarkable necrotic and regenerative fibers. Sarcoplasm and capillaries expressed C5b9 and myxovirus resistance protein 1. Non-necrotic fibers in perifascicular regions expressed MHC-II. Steroid therapy did not sufficiently control cGVHD-related IM, and the patient was concurrently treated with an immunosuppressant. Our findings show that IM is a key manifestation of cGVHD and that the expression of interferon-inducible proteins in muscle pathology is useful for identifying cGVHD-related IM.

Differential diagnosis of necrotizing myopathy

PURPOSE OF REVIEW

Necrotizing myopathy is a broad term. It includes patients with the recently described immune-mediated necrotizing myopathies (IMNM) who have specific antibodies, such as anti-hydroxy-3-methylglutaryl-CoA reductase or anti-signal recognition particle, seronegative phenotypes that can be associated with cancer, and other types of myositis and connective tissue diseases involving necrotic muscle fibers as a characteristic pathologic feature. Necrotizing myopathies that are not immune-mediated, such as those caused by drugs, dystrophies, infections, or even hypothyroidism are also included. The purpose of this review is to address the differential diagnosis of these disorders.

RECENT FINDINGS

New IMNM have been described over the last few years, some of them related with checkpoint inhibitors, drugs that are being increasingly used in cancer treatment. Necrotizing myopathy has also been reported in association with specific phenotypes and autoantibodies (e.g. anti-Mi2 dermatomyositis, antisynthetase syndrome, and myositis associated with antimitochondrial antibodies). Rarer cases associated with graft-versus-host disease and severe acute respiratory syndrome coronavirus 2 infection are also emerging.

SUMMARY

Differentiation between patients with IMNM and those without the superimposed autoimmune phenomena helps clinicians determine the best individualized approach to use and the appropriate immunosuppressive therapy, whenever needed.