Conclusions

This case highlights the diagnostic complexity of severe pulmonary DS in APL despite dexamethasone prophylaxis. The close temporal relationship with ATRA initiation, hyperleukocytosis, fluid retention, predominant pulmonary involvement, absence of bacterial growth from respiratory samples, and subsequent improvement after corticosteroid intensification supported DS as the predominant mechanism of respiratory deterioration. Early escalation to pulse methylprednisolone therapy, combined with HFNC support and awake prone positioning, was associated with rapid clinical, oxygenation, and radiographic improvement, avoiding invasive mechanical ventilation in a high-risk patient. This case reinforces the importance of early recognition and individualized treatment intensification in patients with severe pulmonary DS, rapidly progressive hypoxemic respiratory failure, and a high procedural risk associated with invasive mechanical ventilation because of severe thrombocytopenia or coagulopathy.