Stage and screen actor Mr West, 79, talks about Ms Scales' condition in a new More4 documentary, Grand Canal Journeys.
The actress, now 81, is best known for her role as Basil Fawlty's wife Sybil in the comedy Fawlty Towers but has continued to notch up screen roles.
Mr West, who has joined EastEnders, tells the programme, which is broadcast later this month, that Ms Scales suffers from "a sort of mild Alzheimer's".
The couple have been navigating Britain's canals on a slow boat ever since they borrowed a friend's boat for a fortnight in the 1970s.
And Mr West says that the journeys are perfect for his wife because of the difficulties with her memory.
"She can't remember things very well, but you don't have to remember things on the canal," he says. "You can just enjoy things as they happen, so it's perfect for her."
Scales says that she was determined not to let the condition keep her from the stage. "I always say I want to die on the eighth curtain call," she says.
"Eight will mean the show's been rather a success. I just hope I'm somewhere near the middle and have been reasonably good."