Michael is 42 years old and has seen the GP recurrently over the last few months with a discharging left ear. He has had multiple courses of antibiotics but the symptoms persist. He is on no regular medications and is normally fit and well. The discharge has no odour. Michael says his mother tells him he had recurrent ear infections as a child. He feels his hearing in the left ear has gradually got worse over the last few months.

On examination today, there is purulent discharge in the left ear canal. You note a retraction pocket in the tympanic membrane and some granulation tissue.

What is the most likely diagnosis?