Rhabdomyosarcoma with Bone Marrow Metastasis Masquerading as Acute Leukaemia: A Case Report

Rhabdomyosarcoma (RMS) is a malignant mesenchymal tumour with skeletal muscle differentiation. Three subtypes of RMS are recognised, namely embryonal, alveolar, and pleomorphic. Of these, the alveolar and embryonal subtypes are common in childhood and adolescence. The present case illustrates an example of paediatric RMS with diffuse bone marrow metastasis. A 12-year-old male child was referred as a case of bicytopenia under evaluation and initially had complaints of cough, cold and fever for one month. There was also a history of breathing difficulty, weight loss, loss of appetite and lethargy. The child developed respiratory distress and required oxygen support. A Computed Tomography (CT) scan of the chest revealed left moderate pleural effusion, consolidation of the left upper and lower lobes, and mild pericardial effusion. The child underwent bone marrow aspiration and flow cytometry. The bone marrow aspiration showed 35% blasts, and the flow cytometry report was suggestive of acute erythroid leukaemia/acute megakaryoblastic leukaemia. Meanwhile, the child developed haemorrhagic pleural effusion, and a Contrast-enhanced Computed Tomography (CECT) scan of the chest showed a large mediastinal mass encasing the airway and large vessels (aorta, pulmonary vein and superior vena cava). The child was planned for an Ultrasonogram (USG) guided biopsy under high-risk consent. During the course of the procedure, the child developed sudden cardiac arrest and was declared dead. Biopsy tissue from the mediastinal mass was received, and based on microscopic and immunohistochemistry analysis, the final diagnosis of RMS with diffuse bone marrow metastasis was made. The present case is known for its diagnostic challenge due to the lack of characteristic clinical presentation.