BackgroundSpontaneous intramuscular hemorrhage (SIH) is a rare but life-threatening complication of dermatomyositis (DM). The pathogenetic mechanism and management of intramuscular hematoma in these patients remains unclear. Here we discuss a case of recurrent hemorrhage in a patient with cancer-associated DM, and review the relevant literature for timely diagnosis and treatment.Case presentationA 53-year-old male patient presented with rashes, muscle weakness, and dysphagia and was diagnosed with DM. During treatment, he developed SIH of the arm and right psoas major muscle successively. MRI showed extensive edema of the right shoulder girdle muscle and muscle groups of the upper arm. During the second SIH, a CT scan showed new-onset hematoma formation in the right psoas major muscle. The detection of D-dimer, thrombin-antithrombin III complex (TAT), plasmin-α2-plasmininhibitor complex (PIC) and tissue plasminogen activator-inhibitor complex (t-PAIC) indicated predominant hyperfibrinolysis over thrombosis. Blood transfusion and supportive treatment were immediately performed, and the hematoma did not expand. However, his abdominal distension was not relieved after active treatment. Further electronic gastroscopy discovered gastric sinus ulcers, and histopathology of the biopsy confirmed signet-ring cell carcinoma.ConclusionsAlthough patients with cancer-associated DM have an increased risk of thrombosis, prophylactic anticoagulation therapy needs deliberate consideration. It is important to monitor the coagulation parameters dynamically during anticoagulation therapy. Especially when the level of D-dimer is high, and it is uncertain whether the patient is in a state of thrombosis or hyperfibrinolysis, the detection of TAT, PIC, t-PAIC can help to determine whether to initiate anticoagulation therapy.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12891-023-06651-z.