A case of paraneoplastic amyopathic dermatomyositis triggered by cancer treatment involving atezolizumab

Abstract

Dermatomyositis is a rare inflammatory myopathy. Twenty per-cent of cases may present without muscle weakness, also known as amyopathic dermatomyositis (ADM). The exact pathogenesis of dermatomyositis is unknown but has been proposed to be immune-mediated. The condition is known for its strong association with malignancy, particularly in the presence of anti-TIF1- gamma autoantibody. We herein present a case of anti-TIF1- gamma ADM in a cancer patient, developed following the administration of palliative chemotherapy and immunotherapy with Atezolizumab. A 62-year- old female with extensive-stage small cell lung carcinoma (SCLC) was referred to dermatology with a four-month history of pruritic rash and periorbital oedema. The symptoms started after the first cycle of Carboplatin/ Etoposide/Atezolizumab and persisted despite a two-month course of oral steroid. The patient reported photosensitivity but denied muscle weakness. Examination revealed classical signs of dermatomyositis. The diagnosis was further supported by skin biopsy, demonstrating interface reaction with dermal mucin deposition, a superficial lymphocytic infiltrate, and the presence of eosinophils suggesting the possibility of drug-triggered connective tissue disease. Blood tests were positive for ANA 1:160 with speckled pattern, anti-TIF1- gamma and PM-Scl100. Creatine kinase, C3, C4, dsDNA, and histone antibodies were normal. A diagnosis of paraneoplastic ADM, likely triggered by Atezolizumab, was subsequently made. The patient was advised about sun avoidance and commenced on topical methylprednisolone 0.1% ointment. Dermatomyositis in the context of cancer is well described and there are many reports of dermatomyositis following immunotherapy, most of them expressing anti-TIF1- gamma antibodies. On the other hand, ADM has been rarely described. It is important that clinicians are aware of the possibility of ADM as part of the spectrum of cutaneous adverse events related to immune-checkpoint inhibitors. These patients will benefit from early intervention and close follow-up.