A 15-year-old female student developed upper leg pain and back discomfort. Five weeks later, she noticed weakness in her arms and particularly in her legs, with associated pins and needles and numbness. Her leg weakness was worse in the morning, but progressed over 10 days. She had had no flu or cold symptoms, diarrhoea, rash or joint pain. Two days prior to hospital admission, she required help from her mother to dress. She then had difficulty getting up from a chair or going upstairs.