Capillary leak syndrome (CLS) is a rare condition characterised by increased capillary permeability, with subsequent hypoalbuminemia and hypotension, leading to an increased risk of shock and death. We present the case of a patient with anti-transcriptional intermediary factor 1γ dermatomyositis that developed CLS one week after starting treatment with rituximab and prophylactic co-trimoxazole. The patient was admitted to the Intensive Care Unit (ICU), recovered after treatment with intravenous immunoglobulin, albumin, and Ringer lactate, but died a month after the discharge due to a poorly differentiated hepatocarcinoma diagnosed in the ICU.