Chronic Myopathy Associated With Anti-Signal Recognition Particle Antibodies Can Be Misdiagnosed As Facioscapulohumeral Muscular Dystrophy

Guidelines for genetic testing of muscle and neuromuscular junction disorders

Despite recent advances in the understanding of inherited muscle and neuromuscular junction diseases, as well as the advent of a wide range of genetic tests, patients continue to face delays in diagnosis of sometimes treatable disorders. These guidelines outline an approach to genetic testing in such disorders. Initially, a patient's phenotype is evaluated to identify myopathies requiring directed testing, including myotonic dystrophies, facioscapulohumeral muscular dystrophy, oculopharyngeal muscular dystrophy, mitochondrial myopathies, dystrophinopathies, and oculopharyngodistal myopathy. Initial investigation in the remaining patients is generally a comprehensive gene panel by next-generation sequencing. Broad panels have a higher diagnostic yield and can be cost-effective. Due to extensive phenotypic overlap and treatment implications, genes responsible for congenital myasthenic syndromes should be included when evaluating myopathy patients. For patients whose initial genetic testing is negative or inconclusive, phenotypic re-evaluation is warranted, along with consideration of genes and variants not included initially, as well as their acquired mimickers.

Factors associated with refractory autoimmune necrotizing myopathy with anti-signal recognition particle antibodies

Background

Autoimmune necrotizing myopathy with anti-signal recognition particle antibodies (ANM-SRP) is regarded as refractory myositis, whereby some patients respond poorly to conventional immunosuppression and require B cell depletion treatment. This study aimed to evaluate factors associated with refractory ANM-SRP.

Results

Clinical and pathological data from 48 patients with ANM-SRP were collected. We followed up clinical symptoms and image changes over 12 months. Univariate and multivariate analyses were undertaken to determine the associations between variables of interest and poor response to therapy. Refractory ANM-SRP appeared in 32.5% of patients who showed no or minimal improvement after 12 months of steroid therapy. The clinical risk factors for refractory patients were being male (OR, 19.57; P < 0.001), severe muscle weakness (OR, 7.51; P < 0.001) and concurrent interstitial lung disease (OR, 39.70; P < 0.001). The imaging refractory-related factor was the fatty infiltration rate of thigh muscles over 3 months (P = 0.022) and the pathological factor associated with refractory ANM-SRP was the high expression of B cell activating factor receptor (BAFF-R) in muscle (P = 0.036).

Conclusion

Being male, severe muscle weakness, concurrent interstitial lung disease, quick development of muscle fatty infiltration and more BAFF-R and B lymphocyte infiltration in muscle indicate a poor response to immunosuppressive therapy in patients with ANM-SRP.

[Inpatients with facioscapulohumeral muscular dystrophy in specialized institutions in Japan from 1999 to 2013-Clinical condition changes and causes of death]

We analyzed the registration data of inpatients with facioscapulohumeral muscular dystrophy (FSHD) receiving care at 27 specialized institutions for muscular dystrophy in Japan from 1999 to 2013 using data from October 1 of each year. The number of inpatients of each year ranged from 63 to 72 (67.1 ± 3.3) throughout the study period. Those aged over 50 years gradually increased during the study period, while the oldest inpatient was 82.8 years old. Most could not walk. The rate of respirator dependency increased from 21.0% in 1999 to 71.0% in 2013, while the rate of patients receiving oral nutrition was 98.4% in 1999 and then reduced to 75.4% in 2013. There were 36 death cases reported in the database, including 15 patients with respiratory failure and 4 with heart failure. Our findings indicate that FSHD patients in a severe condition are impacted by respiratory and nutritional problems and their prognosis for survival is related to respiratory failure.

Concurrent positive anti-3-hydroxy-3-methylglutaryl-coenzyme a reductase antibody with reducing body myopathy: Possible double trouble

Anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase myopathy is less common in children but has been associated with more favorable prognosis than adult patients after immunotherapies. We report anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase antibody positivity in a 6-year-old boy with progressive muscle weakness, scoliosis, spinal rigidity, multiple joint contractures, mild left ventricular hypertrophy, and elevated serum creatine kinase. In contrast to most of previously reported pediatric anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase myopathy, he showed little response to immunotherapies. Muscle biopsy contained changes suggestive of myofiber necrosis and regeneration and reducing bodies. The diagnosis of reducing body myopathy was later confirmed by reported c.368A>G (p.His123Arg) mutation in the FHL1 gene. Although the level of association between these two conditions is still inconclusive, this is the first report of concurrent positive anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase antibody with reducing body myopathy emphasizing the possibility of co-occurrence of immune mediated necrotizing myopathy and muscular dystrophy and importance of comprehensive diagnostic investigations in unusual cases.

A pattern-based approach to the interpretation of skeletal muscle biopsies

The interpretation of muscle biopsies is complex and provides the most useful information when integrated with the clinical presentation of the patient. These biopsies are performed for workup of a wide range of diseases including dystrophies, metabolic diseases, and inflammatory processes. Recent insights have led to changes in the classification of inflammatory myopathies and have changed the role that muscle biopsies have in the workup of inherited diseases. These changes will be reviewed. This review follows a morphology-driven approach by discussing diseases of skeletal muscle based on a few basic patterns that include cases with (1) active myopathic damage and inflammation, (2) active myopathic damage without associated inflammation, (3) chronic myopathic changes, (4) myopathies with distinctive inclusions or vacuoles, (5) biopsies mainly showing atrophic changes, and (6) biopsies that appear normal on routine preparations. Each of these categories goes along with certain diagnostic considerations and pitfalls. Individual biopsy features are only rarely pathognomonic. Establishing a firm diagnosis therefore typically requires integration of all of the biopsy findings and relevant clinical information. With this approach, a muscle biopsy can often provide helpful information in the diagnostic workup of patients presenting with neuromuscular problems.

Myositis-specific autoantibodies, a cornerstone in immune-mediated necrotizing myopathy

Over the past few years, myositis-specific autoantibodies played an increasing role in the inflammatory idiopathic myositis definition. They became the critical immunological marker for immune-mediated necrotizing myopathy diagnosis (IMNM) since the paradigm switch from histological to serological criteria. This review is focused on the key role of the anti-signal recognition particle (anti-SRP) and the anti-3-Hydroxy-3-MethylGlutaryl-Coenzyme A Reductase (anti-HMGCR) antibodies in immune-mediated necrotizing myopathy. Anti-SRP and anti-HMGCR antibodies are robust diagnostic tools in case of both the classical subacute form and the slowly progressive form of IMNM that may mimic muscular dystrophy. Anti-SRP and anti-HMGCR patients share clinical, biological and histological features with some antibody-associated specificity. Anti-SRP patients harbour more severe muscle weakness and atrophy with severe muscle damage on magnetic resonance imaging study. Approximately 10-20% of anti-SRP patients develop extramuscular symptoms, especially lung interstitial disease. Conversely, anti-HMGCR patients are often associated with statin exposure. In both cases, patients have a poor outcome with frequent relapse and the use of combined immunotherapy. Of note, various data suggest a direct pathogenic role of these antibodies reinforcing the interest in targeted therapeutic strategy.

Bench to bedside review of myositis autoantibodies

Idiopathic inflammatory myopathies represent a heterogeneous group of autoimmune diseases with systemic involvement. Even though numerous specific autoantibodies have been recognized, they have not been included, with the only exception of anti-Jo-1, into the 2017 Classification Criteria, thus perpetuating a clinical-serologic gap. The lack of homogeneous grouping based on the antibody profile deeply impacts the diagnostic approach, therapeutic choices and prognostic stratification of these patients. This review is intended to highlight the comprehensive scenario regarding myositis-related autoantibodies, from the molecular characterization and biological significance to target antigens, from the detection tools, with a special focus on immunofluorescence patterns on HEp-2 cells, to their relative prevalence and ethnic diversity, from the clinical presentation to prognosis. If, on the one hand, a notable body of literature is present, on the other data are fragmented, retrospectively based and collected from small case series, so that they do not sufficiently support the decision-making process (i.e. therapeutic approach) into the clinics.