Eosinophils in hereditary and inflammatory myopathies

Area of Science:

• Neurology
• Pathology
• Genetics

Background:

• Eosinophilic myositis is not definitively linked to limb girdle muscular dystrophy 2A (LGMD2A).
• Understanding eosinophil presence in muscle biopsies is crucial for accurate myopathy diagnosis.

Purpose of the Study:

• To investigate if eosinophilic myositis is a specific histopathological feature of LGMD2A.
• To analyze the number and location of eosinophils in skeletal muscle biopsies across various neuromuscular disorders and controls.

Main Methods:

• Analysis of skeletal muscle biopsies (n=100) from patients with genetically confirmed myopathies (LGMD2A, LGMD2B, LGMD2L, FSHD, dystrophinopathy), idiopathic inflammatory myopathies (sIBM, DM, PM), amyotrophic lateral sclerosis, and normal controls.
• Giemsa and modified hematoxylin/eosin staining were used to quantify and locate eosinophils.
• Statistical analysis compared eosinophil counts between groups and correlated them with clinical parameters.

Main Results:

• Eosinophil counts were significantly higher in LGMD2A, polymyositis (PM), dermatomyositis (DM), and sporadic inclusion body myositis (sIBM) compared to controls.
• A significant overlap in eosinophil numbers was observed across all disease groups, including other myopathies.
• Eosinophils were predominantly found in endomysial and intra-/perivascular locations, with no correlation to age, disease duration, or other histological changes.

Conclusions:

• Eosinophils in skeletal muscle biopsies represent an unspecific histological finding.
• Their presence is not unique to LGMD2A and is observed across a spectrum of hereditary myopathies, inflammatory myopathies, and amyotrophic lateral sclerosis.