Clinical Course, Myopathology and Challenge of Therapeutic Intervention in Pediatric Patients with Autoimmune-Mediated Necrotizing Myopathy

Asymptomatic HyperCKemia in the Pediatric Population: A Prospective Study Utilizing Next-Generation Sequencing and Ancillary Tests

BACKGROUND AND OBJECTIVES

Persistent elevation of serum creatine kinase levels (hyperCKemia) as an isolated manifestation presents a diagnostic challenge. Genetic myopathies are frequently involved; however, studies using next-generation sequencing (NGS) in pediatric patients are lacking, and the significance of genetic aberrations remains poorly understood. This study, therefore, aimed to investigate the relevance of NGS and the support of contemporary diagnostic tools in the diagnosis of pediatric asymptomatic hyperCKemia.

METHODS

This was a prospective cohort study enrolling pediatric (0-18 years old) patients meeting the predefined criteria for asymptomatic/paucisymptomatic hyperCKemia, excluding DMD gene deletion/duplication, recruited from a referral center. NGS, muscle MRI, EMG, and muscle biopsies with immunolabeling and inflammatory markers were performed according to a prespecified protocol. Data analysis was performed using descriptive/univariate statistics and Bayesian logistic regression.

RESULTS

The series comprised 65 patients (78% male). NGS diagnosis was achieved in 55% of the cohort, with 70% of the pathogenic variants involving 7 genes (DMD, CAPN3, ANO5, DYSF, RYR1, GAA, and CAV3). The diagnostic rate was similar across all age groups; however, the gene profiles varied between the childhood and juvenile groups. EMG yielded myopathic features in 48% of the investigated cases, being predictive for diagnosis (p < 0.05; odds ratio [OR] 13.484, 95% CI 1.358-705.297). MRI showed normal (64%), focal fatty change (26%), or short-tau inversion recovery hyperintensity (10%) profiles, which were not predictive of diagnosis but supported muscle biopsy indications. Muscle biopsy provided a significant diagnostic effect (p < 0.05; OR 0.028, 95% CI 0.001-0.238), contributing to myopathologic features clarifying the variant pathogenicity and identifying inflammatory myopathies. The diagnoses remained inconclusive and unresolved in 14% and 29% of the cohorts, respectively. The diagnostic rate for patients with CK levels below the threshold of 3× was 42%. In multivariate analysis, NGS was the only variable achieving a significant diagnostic effect (β = 9.85, 95% CI 4.65-16.09).

DISCUSSION

NGS, as the primary diagnostic tool for investigating hyperCKemia in the pediatric population, yielded a higher diagnostic rate. However, muscle biopsies are necessary to define variants of uncertain pathogenicity and aid in identifying inflammatory myopathies. EMG and MRI may play a role in hyperCKemia characterization, guiding the decision to perform muscle biopsy. The primary limitation of this study was that not all ancillary tests were performed in all recruited patients owing to ethical restrictions, which lowered the power of the predictive analysis.

Anti-SRP myositis: a diagnostic and therapeutic challenge

BACKGROUND

Anti-signal recognition protein (anti-SRP) myopathy is a rare idiopathic inflammatory myopathy in children. Herein, a 3-year-old patient with severe anti-SRP myopathy showing a rapidly progressive disease course is presented in order to increase the awareness of pediatricians about idiopathic inflammatory myopathies.

CASE PRESENTATION

A previously healthy 3-year-old girl presented with progressive symmetrical proximal muscle weakness that caused difficulty in climbing stairs for two months prior to evaluation, and a marked elevation of the serum creatine kinase levels. A skeletal muscle biopsy revealed necrotic and regenerating processes, with mild inflammatory changes. Myositis-specific and associated autoantibodies tested by the immunoblot method were positive for anti-SRP. Pulse corticosteroid, intravenous immunoglobulin, and methotrexate were administered. However, muscle weakness progressed, respiratory distress and dysphagia developed. Rituximab was initiated. While on rituximab treatment, she was able to walk independently and muscle enzymes were within normal range at the 15th month of diagnosis.

CONCLUSION

Early diagnosis of patients with anti-SRP myositis is important to control inflammation and prevent disease progression and complications. To our knowledge, our patient is the youngest case reported in the literature and was successfully treated with rituximab added to conventional therapy.

Plasma Exchange in Anti-Signal Recognition Particle Myopathy: A Systematic Review and Combined Analysis of Patient Individual Data

Anti-signal recognition particle myopathy (anti-SRP myopathy) is a rare subtype of immune-mediated inflammatory myopathy characterized by muscle weakness and anti-SRP autoantibodies. Although plasma exchange (PE) is used in severe cases, its role remains unclear. A systematic review was conducted following PRISMA guidelines, identifying 23 patients with anti-SRP myopathy treated with PE. Data on demographics, clinical features, laboratory findings, treatments, and outcomes were analyzed combining individual patient data if available. Sixteen (69.6%) patients were male, with muscle weakness as the predominant symptom in 100% of cases. After PE, most patients showed improvement in symptoms, and the proportion of patients with muscle weakness was reduced (p = 0.001). Relapse occurred in 17.4% of the cases. The incidence of adverse events was low (8.7%). Despite limitations, including a small sample size and heterogeneous data, our systematic review suggests that PE may be effective in inducing remission and controlling symptoms in anti-SRP myopathy, particularly in severe cases. Since evidence on PE in anti-SRP myopathy is limited, further research, including prospective multicenter studies, is warranted to understand better its efficacy and safety and establish its role in treatment algorithms.

Six Years Follow-Up of an 11-Year-Old Girl with Anti-HMGCR Myopathy

Anti-HMGCR myopathy is decribed as an immune-mediated necrotizing myopathy which is characterised by subacute, progressive proximal muscle weakness and elevated creatine kinase (CK) level. In pediatric population, anti-HMGCR myopathy has been reported solely as small case reports, albeit rare. Although treatment consensus has not yet been established, proper treatment with several immunomodulators to include IVIg can show remarkable improvement. We report an 11-year-old-girl diagnosed with anti-HMGCR myopathy with 6 years of follow-up.

Case report: Diagnostic clues for anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase myopathy in pediatric patients

Introduction

Anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) myopathy is a recently recognized pathology, but appears less common in children and the characteristics of pediatric cases remain unclear.

Case report

We report a pediatric case of anti-HMGCR myopathy accompanied by skin rash. Motor function and serum creatine kinase level normalized after combinational treatment including early intravenous immunoglobulin, methotrexate, and corticosteroid.

Literature review

We searched PubMed and identified reports with detailed clinical information of 33 pediatric patients <18 years old with anti-HMGCR myopathy. Among these 33 patients and our own case, skin rash and maximum serum creatine kinase level >5,000 IU/L were observed in 44% (15 patients) and 94% (32 patients), respectively. Skin rash was present in 15 of the 22 patients (68%) ≥7 years old and none of the 12 patients (0%) <7 years old. Among the 15 patients with skin rash, 12 (80%) presented with erythematous rash.

Conclusion

Erythematous skin rash may offer a clue to the diagnosis of anti-HMGCR myopathy in children with muscle weakness and serum creatine kinase level >5,000 IU/L in the absence of other myositis-specific antibodies, particularly in patients ≥7 years old. Our results suggest the importance of early anti-HMGCR testing in pediatric patients with these manifestations.

A Child with Refractory and Relapsing Anti-3-Hydroxy-3-Methylglutaryl-Coenzyme A Reductase Myopathy: Case-Based Review

BACKGROUND/OBJECTIVE

Anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (anti-HMGCR) myopathy is rare in children. Here, we present a boy with relapsing refractory anti-HMGCR myopathy along with a systematic literature review.

CASE REPORT

17-year-old boy with five years of muscle weakness, rash, high creatinine kinase (CK) levels, and muscle biopsy compatible with inflammatory myopathy was diagnosed with juvenile dermatomyositis. He was treated with corticosteroids, intravenous immunoglobulin (IVIG), and methotrexate. His muscle weakness improved with this treatment although never completely resolved. CK levels decreased from ∼15000 U/L to ∼3000 U/L. At the age of 15, muscle weakness relapsed after an upper respiratory tract infection; pulse corticosteroid treatment was administered. The re-evaluated muscle biopsy showed a necrotizing pattern and the HMGCR antibody was positive confirming anti-HMGCR myopathy when he was 16. The diagnostic delay was 50 months. Disease activity was monitored by Medical Research Council score, MRI and functional tests. Despite corticosteroids, methotrexate, IVIG, cyclosporine A, and rituximab therapies, muscle weakness improved only slightly during the first three months and remained stable afterwards.Results of the Literature Search:We identified 16 articles describing 50 children (76% female) with anti-HMGCR myopathy by reviewing the English literature up to March 1st, 2022. Proximal muscle weakness was the most common clinical symptom (70.8%). Corticosteroids (84.8%), IVIG (58.7%), and methotrexate (56.5%) were preferred in most cases. Complete remission was achieved in nine patients (28.1%).

CONCLUSION

Diagnosis and management of children with anti-HMGCR myopathy are challenging. Complete remission is achieved in only one third of these patients. Imaging biomarkers may aid treatment.

Pediatric immune-mediated necrotizing myopathy

Immune-mediated necrotizing myopathy (IMNM) is a type of inflammatory myopathy. Most patients with IMNM produce anti-3-hydroxy-3-methylglutaryl coenzyme A reductase or anti-signal-recognition particle autoantibodies. IMNM is much rarer in children than in adults. We conducted this mini review focusing on pediatric IMNM to present current evidence regarding its epidemiology, clinical characteristics, diagnosis, and treatment. Our findings indicate that pediatric IMNM often causes severe muscle weakness and is refractory to corticosteroids alone. Furthermore, delayed diagnosis is common because of the clinicopathological similarity between IMNM and inherited myopathy. Raising awareness regarding pediatric IMNM may facilitate early diagnosis and effective treatment.

Muscle imaging in myositis: MRI, US, and PET

Imaging is an important tool in the evaluation of idiopathic inflammatory myopathies. It plays a role in diagnosis, assessment of disease activity and follow-up, and as a non-invasive biomarker. Among the different modalities, nuclear magnetic resonance imaging (MRI), ultrasound (US), and positron emission tomography (PET) may have the most clinical utility in myositis. MRI is currently the best modality to evaluate skeletal muscle and provides excellent characterization of muscle edema and fat replacement through the use of T1-weighted and T2-weighted fat suppressed/STIR sequences. Although MRI can be read qualitatively for the presence of abnormalities, a more quantitative approach using Dixon sequences and the generation of water T2 parametric maps would be preferable for follow-up. Newer protocols such as diffusion-weighted imaging, functional imaging measures, and spectroscopy may be of interest to provide further insights into myositis. Despite the advantages of MRI, image acquisition is relatively time-consuming, expensive, and not accessible to all patients. The use of US to evaluate skeletal muscle in myositis is gaining interest, especially in chronic disease, where fat replacement and fibrosis are detected readily by this modality. Although easily deployed at the bedside, it is heavily dependent on operator experience to recognize disease states. Further, systematic characterization of muscle edema by US is still needed. PET provides valuable information on muscle function at a cellular level. Fluorodeoxyglucose (FDG-PET) has been the most common application in myositis to detect pathologic uptake indicative of inflammation. The use of neurodegenerative markers is now also being utilized for inclusion body myositis. These different modalities may prove to be complementary methods for myositis evaluation.

Juvenile Dermatomyositis

Die juvenile Dermatomyositis (JDM) ist die häufigste chronische entzündliche Myopathie des Kindesalters. In dieser Übersicht soll der aktuelle Kenntnisstand hinsichtlich der Diagnostik, Behandlung und Überwachung der JDM dargestellt werden. So liegen häufig myositis-spezifische Antikörper vor, die mit klinischen Phänotypen und dem Verlauf der Erkrankung korrelieren. Typ I Interferone spielen eine wichtige Rolle in der Pathogenese der Erkrankung. Möglicherweise kann diese Beobachtung in der Zukunft zu gezielten Therapien führen. Da langfristig schwerwiegende Komplikationen, wie z. B. Kalzinosen oder Lipodystrophie, drohen, besonders bei auf Dauer unzureichend kontrollierter Erkrankung, ist eine möglichst rasche und effektive Behandlung anzustreben. Zu diesem Zweck sollte eine intensive Remissionsinduktionstherapie, gefolgt von einer zielgerichteten Therapie angestrebt werden. Verschiedene validierte Messinstrumente stehen zur Verfügung, um den Verlauf der Erkrankung zu beurteilen. Die Pro-KIND-Initiative der Gesellschaft für Kinder- und Jugendrheumatologie hat Praxis- und Konsens-basiert in Deutschland sowohl eine diagnostische als auch eine Treat-to-Target-Behandlungsstrategie entwickelt. Im Rahmen nationaler und internationaler Kollaborationen soll sich die Behandlung der JDM in der Zukunft weiter verbessern.