You are seeing a 50-year-old male in A&E who has presented with weakness. On further questioning, the patient informs you that over the last two months he has noticed bilateral weakness in his legs, hands, feet, shoulders and hips. He has also experienced difficulty in swallowing, clumsiness, double vision and fatigue. On examination you note the presence of reduced deep tendon reflexes and muscle wasting. The patient has no past medical history and has been in good health recently. What is the most likely diagnosis?