Focal myositis: A review.

Area of Science:

• Rheumatology
• Neurology
• Pathology

Background:

• Focal myositis is a rare, benign dysimmune disease within the inflammatory myopathies.
• Triggering factors are poorly understood, though associations with nerve lesions, trauma, and autoimmune diseases exist.
• It presents as an isolated inflammatory pseudotumor, typically in a single skeletal muscle, often the lower limbs.

Purpose of the Study:

• To describe the clinical presentation, diagnostic features, and management considerations for focal myositis.

Main Methods:

• Clinical presentation analysis
• Electromyography (EMG) findings
• Magnetic Resonance Imaging (MRI) characteristics
• Histopathological examination
• Serum creatine kinase (CK) level assessment

Main Results:

• Presents as a rapidly growing solitary muscle mass.
• EMG shows spontaneous activity and a myopathic pattern.
• MRI reveals contrast-enhanced, enlarged muscle, hyper-intense on FAT-SAT T2 images, sparing adjacent structures.
• Serum CK levels are moderately elevated; systemic inflammation markers are usually absent.
• Histology shows varied fiber size, T CD4+ lymphocyte and macrophage infiltrates, and fibrosis.

Conclusions:

• Focal myositis is a distinct entity with characteristic imaging and histological findings.
• Differential diagnosis is crucial, including other focal myositides.
• Corticosteroid therapy is indicated for significant pain, nerve involvement, associated autoimmune conditions, or elevated inflammatory markers (CRP, CK).