The Myocardial Accumulation of Aggregated Desmin Protein in a Case of Desminopathy with a de novo DES p.R406W Mutation.

Desminopathy is a cardiac and skeletal myopathy caused by disease-causing variants in the desmin (DES) gene and represents a subgroup of myofibrillar myopathies, where cytoplasmic desmin-postive immunoreactivity is the pathological hallmark. We herein report a 28-year-old Japanese man who was initially diagnosed with sporadic hypertrophic cardiomyopathy with atrioventricular block at 9 years old and developed weakness in the soft palate and extremities. The myocardial tissue dissected during implantation of the ventricular-assisted device showed a dilated phase of hypertrophic cardiomyopathy and intracellular accumulation of proteinase K-resistant desmin aggregates. Genetic testing confirmed a de novo mutation of DES, which has already been linked to desminopathy. As the molecular diagnosis of desminopathy is challenging, particularly if patients show predominantly cardiac signs and a routine skeletal muscle biopsy is unavailable, these characteristic pathological findings of endomyocardial proteinase K-resistant desmin aggregates might aid in clinical practice.

Pembrolizumab on pre-existing inclusion body myositis: a case report.

BACKGROUND: Cases of exacerbation of pre-existing neuromuscular diseases induced by immune checkpoint inhibitors (ICIs) have rarely been reported because patients with autoimmune diseases have generally been excluded from ICI therapy due to the increased risk of exacerbation. We describe the first case of an elderly patient who experienced exacerbation of a previously undiagnosed sporadic inclusion body myositis (sIBM), the most common myopathy in the geriatric population, which was triggered by anti-programmed cell death-1 therapy. CASE PRESENTATION: A 75-year-old man who was receiving pembrolizumab presented with limb weakness. Three years prior, he had noticed slowly progressive limb weakness, but he received no diagnosis. After the first infusion of pembrolizumab, his creatine kinase (CK) levels had increased. The neurological examination and muscle biopsy findings confirmed the diagnosis of sIBM and suggested exacerbation of sIBM induced by pembrolizumab. After the patient's CK levels decreased, pembrolizumab was restarted. The tumor progressed after its treatment with pembrolizumab. The patient died after 15 months of follow-up. CONCLUSIONS: In patients with slowly progressive limb weakness, sIBM should be explored before ICI therapy. In addition, if patients show high CK levels after ICI introduction, it is necessary to confirm whether they have sIBM in order to avoid unnecessary immunosuppressive therapies and assess whether they can tolerate ICI reintroduction.

Inflammatory myopathy with myasthenia gravis: Thymoma association and polymyositis pathology.

Objective: To provide evidence that idiopathic inflammatory myopathy (IM) with myasthenia gravis (MG) frequently shows thymoma association and polymyositis (PM) pathology and shares clinicopathologic characteristics with IM induced by immune checkpoint inhibitors (ICIs). Methods: We analyzed the clinicopathologic features of 10 patients with idiopathic IM and MG identified in 970 consecutive patients with biopsy-proven IM. Results: Seven patients (70%) had thymoma. IM and MG were diagnosed with more than 5-year time difference in 6 thymomatous patients and within 1 year in 1 thymomatous and 3 nonthymomatous patients. Seven thymomatous patients showed rhabdomyolysis-like features with respiratory failure (4/7), dropped head (3/7), cardiac involvement (2/7), and positive anti-acetylcholine receptor (anti-AChR) and anti-titin antibodies (7/7 and 4/6, respectively) but rarely showed ocular symptoms (2/7) or decremental repetitive nerve stimulation (RNS) responses (1/7) at IM diagnosis. Three nonthymomatous patients showed acute cardiorespiratory failure with rhabdomyolysis-like features (1/3), positive anti-AChR and anti-titin antibodies (3/2 and 2/2, respectively), and fluctuating weakness of the skeletal muscle without ocular symptoms (3/3). Muscle pathology showed a PM pathology with infiltration of CD8-positive CD45RA-negative T-lymphocytes (9/9), scattered endomysial programmed cell death 1 (PD-1)-positive cells (9/9), and overexpression of programmed cell death ligand 1 (PD-L1) on the sarcolemma of muscle fibers around the infiltrating PD-1-positive cells (7/9). Conclusion: Rhabdomyolysis-like features, positive anti-AChR antibody without decremental RNS responses, and PD-L1 overexpression are possible characteristics shared by ICI-induced IM. Frequent thymoma association in patients with idiopathic IM and MG may suggest thymoma-related immunopathogenic mechanisms, including dysregulation of the immune checkpoint pathway.