Speculation has swirled onthe back of a recent driver's licence suspension, and a critical independent report highlighted short-term memory deficits late last year.
Sir Tim has now revealed he has been diagnosed with muscle tension dysphonia.
The common voice disorder occurs when muscles around the larynx become tight and prevent the voice box from working efficiently.
He said he had tubes put down his throat to confirm the diagnosis and was keen to keep on top of the condition, considering his voice was his "main form of defence".
Invercargill Mayor Sir Tim Shadbolt reclining in his mayoral office late last year. Photo / Stephen Jaquiery
Despite revealing the condition, he remained tight-lipped on what else was covered in the doctor's visits.
He originally did not rule out making the medical reports public at the time he was awaiting further results.
Asked two weeks ago if memory issues were something he hoped to clear up with the doctor visits, Sir Tim replied "it could be".
Sir Tim has consistently disputed any suggestion his health was affecting his ability to do the job.
"I challenged the councillors when this [my health] was raised. Maybe six to 18 months ago.
"They said you're too weak to be the mayor.
"I said I'd challenge any councillor over 70 to a 100m sprint, a 30m swim, and we'll see who comes out the fittest."
Prime Minister Jacinda Ardern shares a light moment with Invercargill Mayor Tim Shadbolt. Photo / Laura Smith
Sir Tim said nobody took him up on the offer.
The mayor's health was highlighted in the Thomson Report last year which stated many interviewees had noticed a decline in Sir Tim's capabilities.
"Many interviewees reported a range of obvious concerns including short-term memory deficits, confusion, and the need to be closely managed by both council staff and senior councillors in order to chair a council meeting," it said.
Concerns about his performance have continued in the wake of the report.
Sir Tim also opened up further on his relationship with his deputy Nobby Clark which has soured in recent times.
Last month, Sir Tim labelled Clark "Brutus" after he said he should front up over his licence being suspended.
Clark said communication between the pair was limited but he had spoken to him for about an hour on Tuesday.
Asked if they were still talking, Sir Tim said there was still some communication. "Yeah, I saw him in the cafe actually.
"Talk about an awkward moment!"
Sir Tim said calling his deputy ''Monty'' was the "one shred of comedy" left in his life. "People think it has some reference to the male apparatus, it's not apparently.
