Missed hypereosinophilic syndrome in a critically ill patient with systemic lupus erythematosus

A high functioning 74-year-old man with systemic lupus erythematosus presented to the emergency department with acute anxiety. He was found to have elevated cardiac enzymes and admitted to the cardiology service for investigation. In hospital, he developed an erythematous papular rash, and deteriorated to being somnolent and bedridden. He was found to have new multiterritory ischaemic strokes. It was eventually noted that he had persistent eosinophilia, present even on admission, which had been overlooked as the total leucocyte count was normal. Serology for antiphospholipid antibody syndrome (APS) was positive. He was diagnosed with hypereosinophilic syndrome (HES) secondary to new APS, and responded to high-dose steroids. This case highlights the importance of fully evaluating a leucocyte differential to make a diagnosis of HES. We discuss the definition, clinical manifestations, diagnostic approach and management of this important condition.