Paraneoplastic Amyopathic Dermatomyositis Associated With a Bone and Medullary Location of Breast Adenocarcinoma.

Paraneoplastic amyopathic dermatomyositis (ADM) is a rare connective tissue disease presenting with characteristic dermatomyositis-like skin findings in the absence of muscle involvement. It is associated with malignancies in 15%-30% of cases and may portend a fatal outcome, especially when linked to advanced cancers. We report the case of a 58-year-old woman who presented with progressive low back pain and erythroderma. Imaging revealed diffuse bone metastases, and bone biopsy confirmed a poorly differentiated adenocarcinoma of breast origin (estrogen receptor, 60%; progesterone receptor, 35%; GATA3 positive). Simultaneously, dermatological evaluation identified periungual erythema and other cutaneous findings consistent with ADM. The patient was started on endocrine therapy with palbociclib and letrozole, along with corticosteroids and hydroxychloroquine, resulting in partial clinical improvement. However, within six months of diagnosis, she developed severe COVID-19 pneumonia, complicated by pancytopenia and sepsis, and ultimately succumbed to multiorgan failure despite intensive care support. This case underlines the importance of recognizing paraneoplastic ADM as an initial manifestation of malignancy. A multidisciplinary approach is key, but the prognosis largely depends on the cancer's burden and complications such as treatment-induced immunosuppression.