This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Investigation in ophthalmology and miscellaneous topics, Subject name: Ophthalmology
[{'content': 'A 75 year old lady wakes up with sudden painless loss of vision. She gives history of scalp tenderness and cramp like pain on eating. O/E there is a pale disc edema, has an inferior altitudinal field defect. What is the likely cause? \nSelect and explain. \nA. Giant cell aeritis, B. Myasthenia gravis, C. Multiple Sclerosis, D. Neuromyelitis optica', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Symptoms of GCA -such as Headache and tenderness of the temporal aeries and scalp. Jaw claudication, characterized by pain on speaking or chewing, is pathognomonic of GCA,caused by ischaemia of masseter muscle Other symptoms include fever, malaise, anorexia, weight loss, night sweats and joint and muscle pain. GCA is extremely unlikely under 55-60 years. It constitutes an ophthalmic emergency.', 'role': 'assistant'}]