A rare case of severe myositis as paraneoplastic syndrome on breast cancer.

Background: Dermatomyositis and polymyositis are both types of idiopathic inflammatory myositis characterized by inflammation and weakness of proximal skeletal muscles and skin rash.

Case: A 49-year-old Caucasian woman recently diagnosed with breast cancer classified as T1N2M0, stage IIIA, presenting skin rash associated with heliotrope and Gottron's papules. In addition, there was a progression to a severe reduction in proximal muscle strength with severe dysphagia. The initial treatment was conducted, and the patient recovered from all symptoms and followed adjuvant cancer management.

Treatment: At first, high dose of corticosteroid was administered as pulse therapy, and a radical mastectomy was indicated due to the severe symptoms of the paraneoplastic syndrome. Then chemotherapy and radiotherapy were applied, and oral corticoid associated with immunosupressive drug was administered for dermatomyositis control.

Discussion: The association between myositis and an increased risk of cancer has been demonstrated over the years. This patient has a high probability of dermatomyositis diagnosis. The initial treatment with high dose of glucocorticoids may result in an improvement of muscle lesions. Second-line treatment with azathioprine, methotrexate, or cyclophosphamide may be required for aggressive disease. Removal of the cancer induces improvement of paraneoplastic syndrome.

Conclusion: Dermatomyositis can be a clinical manifestation of a paraneoplastic syndrome in patients with breast cancer. It is a rare diagnosis, and there is little evidence to guide treatment until now. It is possible to control the evolution of dermatomyositis with high doses of glucocorticoids in almost all cases; however, in severe cases of paraneoplastic syndrome, cancer treatment should start immediately.