Every case is different, and there is no one single cause, but lots of players report it comes from a fear of missing.
"It's brought on by anxiety and stress," Kevin said.
"Where others have panic attacks, for me it manifested as dartitis."
Dr Duffy says that - perhaps due to its name - players have a tendency to view dartitis as a problem unique to the sport which therefore demands unique solutions.
"It's just another cognitive disorder, so it should be treated that way," she says. "The underlying mechanisms that cause dartitis are the same things that cause any other anxiety disorder."
She recommends cognitive behavioural therapy (CBT) to enable the player to reframe dartitis as a challenge they need to overcome.
Kevin has been trying to conquer the condition with hypnotherapy - and CBT - taking sessions with Chris O'Connor whose company Eccleston Park Hypnotherapy is the official "hypnotherapy partner" of the Professional Darts Players Association (PDPA).
During his sessions, the patient lies on a sofa and is guided into a trance where they are then "hit with all the confidence work and the motivation work", Mr O'Connor said.
"It's all about getting them to visualise an area of their life they want to improve."
After eight sessions, it seemed Kevin's dartitis had been cured for good. But two weeks later, during a televised match at the World Senior Darts tour, the condition returned. "I was really, really disappointed," he said. "I thought it had gone."
He's now back working with Mr O'Connor on cracking the disorder long term.
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