Parkinson's disease (PD) is a long-term degenerative disorder of the central nervous system that mainly affects the motor system.
The symptoms generally come on slowly over time and early in the disease, the most obvious are shaking, rigidity, slowness of movement, and difficulty with walking.
"Got news I wasn't anticipating recently. I've been diagnosed with Parkinson's Disease. Just wanted to let everyone know I'm doing good, staying positive and strong. Devastated by the news, but life goes on. Thanks to those close to me, and especially huge thanks and love to Paula," he wrote on his Twitter and Facebook accounts.
He also said: "Looking back, I realise now that I haven’t felt well for a long time, and I was putting it down to the results of severe stress and the heavy pressures of life that I just assumed we have to put up with these days.
“Eventually, I started to feel so unwell I thought I maybe needed to get it checked out.”
He added: "I just want to reassure all my friends here that I am fine and positive and optimistic, and I remain that way, and nothing changes day to day."
As well as a broadcaster, Gareth O'Callaghan is a psychotherapist, and writer.
"My radio show is and will always be a very big part of my life, as will my writing. Nothing changes there whatsoever."

Got news I wasn't anticipating recently. I've been diagnosed with Parkinson's Disease. Just wanted to let everyone know I'm doing good, staying positive and strong. Devastated by the news, but life goes on. Thanks to those close to me, and especially huge thanks and love to Paula

— Gareth O'Callaghan (@GarethOCal) March 5, 2018