A 52 year old male is seen in ENT clinic with a 3 month history of recurrent left sided ear discharge. He has had 6 courses of antibiotics this year for presumed otitis media. 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?