Search

Mexiletine (NaMuscla™) is indicated for the symptomatic treatment of myotonia in adults with non-dystrophic myotonia. A cardiac assessment is required as mexiletine may have a pro-arrhythmic effect. Long-term safety data supporting the use of mexiletine in patients with non-dystrophic myotonia combined with the extensive clinical experience of an expert group resulted in creation of an algorithm for cardiac monitoring of patients treated with mexiletine. To define the treatment algorithm, several expert workshops including three neurologists, five cardiologists from different French neuromuscular reference centers and one pharmacologist from Italy were set up. These workshops aimed to define the screening and surveillance tools required to ensure the safe use of mexiletine in patients. The recommendations are based on the summary of product characteristics (SmPC), a review of the literature on the safety of mexiletine-treated patients with non-dystrophic myotonia, and the expertise of the authors. The expert group concluded that the cardiac safety profile of mexiletine in these patients appears to be similar to that in the general population. Therefore, patients with non-dystrophic myotonia treated with mexiletine should be monitored as per any patient with cardiac problems who are prescribed a class 1b anti-arrhythmic., Competing Interests: Declaration of competing interest All authors declare consulting fees from Lupin Neuroscience., (Copyright © 2024. Published by Elsevier B.V.)

Dysferlinopathy is a muscle disease characterized by a variable clinical presentation and is caused by mutations in the DYSF gene. The Jain Clinical Outcome Study for Dysferlinopathy (COS) followed the largest cohort of patients (n=187) with genetically confirmed dysferlinopathy throughout a three-year natural history study, in which the patients underwent muscle function tests and muscle magnetic resonance imaging (MRI). We previously described the pattern of muscle pathology in this population and established a series of imaging criteria for diagnosis. In this paper, we describe the muscle imaging and clinical features of a subgroup of COS participants whose muscle imaging results did not completely meet the diagnostic criteria. We reviewed 184 T1-weighted (T1w) muscle MRI scans obtained at the baseline visit of the COS study, of which 106 were pelvic and lower limb only and 78 were whole-body scans. We identified 116 of the 184 patients (63%) who did not meet at least one of the established imaging criteria. The highest number found of unmet criteria was four per patient. We identified 24 patients (13%) who did not meet three or more of the nine established criteria and considered them as "outliers". The most common unmet criterion (27.3% of cases) was the adductor magnus being equally or more affected than the adductor longus. We compared the genetic, demographic, clinical and muscle function data of the outlier patients with those who met the established criteria and observed that the outlier patients had an age of disease onset that was significantly older than the whole group (29.3 vs 20.5 years, p=0.0001). This study expands the phenotypic muscle imaging spectrum of patients with dysferlinopathy and can help to guide the diagnostic process in patients with limb girdle weakness of unknown origin., Competing Interests: Declarations of Competing Interest Authors have no conflict of interest related to the content of this paper., (Copyright © 2023. Published by Elsevier B.V.)

Myostatin is a myokine which acts upon skeletal muscle to inhibit growth and regeneration. Myostatin is endogenously antagonised by follistatin. This study assessed serum myostatin and follistatin concentrations as monitoring or prognostic biomarkers in dysferlinopathy, an autosomal recessively inherited muscular dystrophy. Myostatin was quantified twice with a three-year interval in 76 patients with dysferlinopathy and 38 controls. Follistatin was quantified in 62 of these patients at the same timepoints, and in 31 controls. Correlations with motor function, muscle fat fraction and contractile cross-sectional area were performed. A regression model was used to account for confounding variables. Baseline myostatin, but not follistatin, correlated with baseline function and MRI measures. However, in individual patients, three-year change in myostatin did not correlate with functional or MRI changes. Linear modelling demonstrated that function, serum creatine kinase and C-reactive protein, but not age, were independently related to myostatin concentration. Baseline myostatin concentration predicted loss of ambulation but not rate of change of functional or MRI measures, even when relative inhibition with follistatin was considered. With adjustment for extra-muscular causes of variation, myostatin could form a surrogate measure of functional ability or muscle mass, however myostatin inhibition does not form a promising treatment target in dysferlinopathy., Competing Interests: Declaration of Competing Interest None., (Copyright © 2023. Published by Elsevier B.V.)

This study aims to determine clinically relevant phenotypic differences between the two most common phenotypic classifications in dysferlinopathy, limb girdle muscular dystrophy R2 (LGMDR2) and Miyoshi myopathy (MMD1). LGMDR2 and MMD1 are reported to involve different muscles, with LGMDR2 showing predominant limb girdle weakness and MMD1 showing predominant distal lower limb weakness. We used heatmaps, regression analysis and principle component analysis of functional and Magnetic Resonance Imaging data to perform a cross-sectional review of the pattern of muscle involvement in 168 patients from the Jain Foundation's international Clinical Outcomes Study for Dysferlinopathy. We demonstrated that there is no clinically relevant difference in proximal vs distal involvement between diagnosis. There is a continuum of distal involvement at any given degree of proximal involvement and patients do not fall into discrete distally or proximally affected groups. There appeared to be geographical preference for a particular diagnosis, with MMD1 being more common in Japan and LGMDR2 in Europe and the USA. We conclude that the dysferlinopathies do not form two distinct phenotypic groups and therefore should not be split into separate cohorts of LGMDR2 and MM for the purposes of clinical management, enrolment in clinical trials or access to subsequent treatments., Competing Interests: Declaration of Competing Interest None., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Mutations in RYR1 give rise to diverse skeletal muscle phenotypes, ranging from classical central core disease to susceptibility to malignant hyperthermia. Next-generation sequencing has recently shown that RYR1 is implicated in a wide variety of additional myopathies, including centronuclear myopathy. In this work, we established an international cohort of 21 patients from 18 families with autosomal recessive RYR1-related centronuclear myopathy, to better define the clinical, imaging, and histological spectrum of this disorder. Early onset of symptoms with hypotonia, motor developmental delay, proximal muscle weakness, and a stable course were common clinical features in the cohort. Ptosis and/or ophthalmoparesis, facial weakness, thoracic deformities, and spinal involvement were also frequent but variable. A common imaging pattern consisted of selective involvement of the vastus lateralis, adductor magnus, and biceps brachii in comparison to adjacent muscles. In addition to a variable prominence of central nuclei, muscle biopsy from 20 patients showed type 1 fiber predominance and a wide range of intermyofibrillary architecture abnormalities. All families harbored compound heterozygous mutations, most commonly a truncating mutation combined with a missense mutation. This work expands the phenotypic characterization of patients with recessive RYR1-related centronuclear myopathy by highlighting common and variable clinical, histological, and imaging findings in these patients., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Dysferlinopathies are autosomal recessive muscular dystrophies caused by DYSF mutations, which lead to a reduced amount or a complete lack of dysferlin. One step in dysferlinopathies diagnosis consists in Western blot analysis of proteins extracted from muscle biopsy, or blood monocytes. We have taken advantage of dysferlin expression in monocytes to develop a whole blood flow cytometry (WBFC), using antibodies directed against dysferlin. Six patients were submitted to WBFC analysis and immunofluorescence analysis on monocytes. Results obtained are correlated to Western blot from monocytes and muscle biopsies. The possible usefulness of this flow cytometry analysis in routine diagnosis is presented.