After having scans and getting a firm diagnosis, his health deteriorated rapidly over a year-long period.
"Every month, there would be massive changes, you would just get used to one piece of equipment and it was on to the next.
"He lost the use of his arms and legs, by the end he couldn't eat, only see and hear."
His tale is not unlike many others - one in five people will develop a neurological condition in their lifetime - that increases to one in three if you include strokes.
Brain Awareness Week, from March 16-22, aims to raise funds for neurological research and awareness about the prevalence of neurological conditions.
In 2010, Mrs Stewart decided to bring Malcolm's service crew, co-driver Mike Fletcher and old friend Ray Wilson together to race a car emblazoned with logos for Motor Neurone Disease Association NZ and Neurological Foundation NZ.
Entering classic and historic car categories, they travel the country to spread their message; a project Mrs Stewart funds out of her own pocket.
"The service van is covered in signage and my private ute.
"We are building a new car - the service crew in Dannevirke have the old one and take it to a couple of events there and a few up here."
The foundation funds research into conditions including motor neurone disease, stroke, Alzheimer's, Parkinson's, MS, epilepsy, Huntington disease and brain injury while the association supports people with motor neurone disease and their carers.
"Those outfits struggle with funding so that's what this is about, we are hoping people see the sign and take note because it can happen to anyone," Mrs Stewart said.
"Heart attacks and cancers get publicity because people are out there with it, walking around - you don't see people with MND because it gets to the point where you can't go out, with Malcolm we couldn't go anywhere for six months."
They hope to start the season for 2015 with their new car in about April.
People can take part in Brain Awareness Week by heading to the foundation's NZ website, neurological.org.nz, to read up on the research being done here or make a donation.