An 11-year-old girl, previously fit and well, presented with a 1-week history of feeling unwell, very tired, extremely lethargic and breathless on exertion, on a background of being non-specifically unwell for the previous 2 months. She had no other specific symptoms and was afebrile at the time of presentation. On the morning of presentation, she had an acute onset of severe respiratory distress and was pale, very cold and unable to talk. She reported she had not been to the toilet for most of the previous day and night. Her mother was extremely alarmed by her colour and brought her to her local A&E department by car, although she was unable to walk from the car park and required a wheelchair.