It's a progressive disease so his condition worsens over time.
Times,Sunday Times
It's a progressive disease, which means that gradually over time, more parts of the brain are damaged.
The Sun
It's a relentless progressive disease.
The Sun
He has muscular dystrophy, a progressive disease.
Houston Chronicle
But as the disease progresses so the repair in most patients will fail and that causes progressive disease.
Times, Sunday Times