A 52 year old male presents to the GP with a 3 month history of recurrent left sided ear discharge. You note from his record he has had 6 courses of antibiotics this year for presumed otitis media including from out of hours. Hearing is normal and there is no earache, tinnitus or current history of fever.
On examination today, there is scanty purulent discharge in the left ear canal and a retraction pocket in the tympanic membrane is seen.
What is the most likely diagnosis?