Myopathies in Early Infancy: An Overview and a Case of Early Onset Anti-NXP2-Positive Juvenile Dermatomyositis

S. Didt; N. Rieber; V. Kraus

doi:10.1055/s-0045-1812124

Neuropediatrics, Table of Contents

Neuropediatrics 2025; 56(S 01): S1-S24
DOI: 10.1055/s-0045-1812124

Neuromuscular Disorders

Myopathies in Early Infancy: An Overview and a Case of Early Onset Anti-NXP2-Positive Juvenile Dermatomyositis

Authors

S. Didt

¹Klinik für Kinder- und Jugendmedizin, Technische Universität München, Neuropädiatrie, München, Germany
N. Rieber

²Klinik für Kinder- und Jugendmedizin, Technische Universität München, Pädiatrische Rheumatologie und Infektiologie, München, Germany
V. Kraus

¹Klinik für Kinder- und Jugendmedizin, Technische Universität München, Neuropädiatrie, München, Germany

Abstract

Full Text

Background/Purpose: Neuromuscular diseases (NMDs) in the neonatal period or early infancy are characterized by hypotonia and weakness. They include congenital myopathies, muscular dystrophies and myasthenic syndromes, SMA I, M. Pompe, mitochondriopathies, and, rarely, autoimmune diseases. Diagnostic challenges include negative genetic findings, incomplete phenotypes, and borderline antibody results. We report on a patient (3 years) with dysphagia, progressive weakness, exercise intolerance, social withdrawal, and general misery. Hypotonia and feeding problems have been present since the neonatal period. Neurological examination revealed proximal weakness and myopathic facies. CK levels were repeatedly normal. Muscle ultrasound, NCS, metabolic and myasthenia antibody testing, EEG, and trio-exome were unremarkable. Myositis-specific antibody testing revealed NXP2 antibodies, but whole-body MRI was normal. Evaluation of NXP2 antibody findings.

Methods: Phenotype reassessment and literature review via PubMed.

Results: Repeated analyses confirmed the presence of highly specific NXP2 antibodies for juvenile dermatomyositis (JDM). CMAS-score (27) indicated a myopathic phenotype, and fluctuating erythema on the cheeks was conspicuous. Pathognomonic heliotrope rash and Gottron's papules were absent. Anti-NXP2-positive inflammatory myositis is known to present with atypical skin manifestations, muscular involvement, and dysphagia. In early disease stages, CK levels can be normal and symptoms nonspecific. We diagnosed anti-NXP2-positive JDM and started treatment with corticosteroids and methotrexate.

Conclusion: This case highlights the challenges of interpreting antibody findings in early onset NMDs with atypical phenotypes. Therefore, myositis-specific antibodies, such as anti-NXP2, are useful for diagnosis, and immunoblot is a reliable testing method. Early-onset and NXP2-associated JDM patients show higher relapse rates and require more intensive immunosuppressive treatment; early diagnosis and treatment are crucial for prognosis.