A 55 year old female presents to you at the acute medical assessment unit with a new onset localised headache that is only present on the left side and localised to the temporal. She complains she has had this headache several times before but it has been bilateral. She also is complaining of tenderness and a nodular feeling in the temporal area. She is not complaining of any visual symptoms. You take some blood tests and you note her ESR is significantly raised. Given your diagnosis, what treatment should be started immediately?