Successful treatment of refractory focal eosinophilic myositis with extra-ocular muscle involvement using tocilizumab: a case report.

Eosinophilic myositis (EM) is a rare subset of idiopathic inflammatory myopathies characterized by prominent eosinophilic infiltration of skeletal muscle. It encompasses focal eosinophilic myositis (FEM), diffuse eosinophilic myositis, and eosinophilic perimyositis. FEM typically presents with single or multiple lesions, most commonly involving the limbs. However, involvement of extra-ocular muscles in FEM is exceedingly rare and has not been well documented. Here, we describe a 65-year-old woman who initially presented with chest wall pain. Magnetic resonance imaging (MRI) and muscle biopsy confirmed multifocal FEM. Notably, the patient also exhibited concomitant involvement of extra-ocular muscles. Treatment with prednisone combined with conventional immunosuppressants led to marked regression of truncal lesions. However, during glucocorticoid tapering, the patient experienced a relapse of myositis confined to the left extra-ocular muscles. She relapsed with left eyelid swelling, tearing, binocular diplopia, exotropia, and impaired adduction of the left eye. This ocular relapse was refractory to glucocorticoids and multiple immunosuppressive agents. Tocilizumab, administered at 8 mg/kg intravenously every 4 weeks, was associated with gradual improvement in diplopia and ocular motility, reduction in extraocular muscle swelling on MRI, and sustained clinical benefit during follow-up. These findings suggest that extra-ocular muscle involvement in FEM may define a more treatment-resistant phenotype, and tocilizumab may represent a promising therapeutic option in this context.