[Myositis: From classification to diagnosis].

Area of Science:

• Rheumatology
• Neurology
• Immunology

Background:

• Idiopathic inflammatory myopathies (IIM) encompass a spectrum of acquired autoimmune diseases primarily affecting muscles.
• IIM subtypes include dermatomyositis, inclusion body myositis, immune-mediated necrotizing myopathies, antisynthetase syndrome, and overlapping myositis.
• These conditions can involve other organs, leading to diverse clinical manifestations beyond muscle weakness.

Purpose of the Study:

• To outline the classification and diagnostic approaches for idiopathic inflammatory myopathies.
• To emphasize the roles of clinical evaluation, electromyography, and serological testing in IIM diagnosis.
• To clarify the indications for muscle biopsy in the diagnostic workup of IIM.

Main Methods:

• Diagnosis is based on clinical examination, patient history, electromyography (EMG), and immunological testing for myositis-specific antibodies (MSAs).
• Repeated or extended antibody testing may be necessary for accurate classification.
• Muscle biopsy is not routinely recommended when clinical and antibody findings are definitive but remains essential for complex cases.

Main Results:

• Accurate classification of IIM subtypes is crucial for appropriate management.
• Myositis-specific antibodies are key diagnostic markers, but their sensitivity can vary.
• Muscle biopsy provides critical etiological information in challenging diagnostic scenarios.

Conclusions:

• Idiopathic inflammatory myopathies require a multi-faceted diagnostic approach.
• The integration of clinical data, serological markers (MSAs), and imaging (EMG) aids in classifying IIM.
• Muscle biopsy remains an indispensable tool for diagnosing ambiguous IIM cases, guiding precise etiological determination.