"Progressive deterioration" refers to a gradual and continuous decline or worsening over time. It implies that something is gradually getting worse or deteriorating, instead of improving or staying the same. Full definition
Typically a variety of chronic (persistent) and / or recurrent diseases develop in these cats, with progressive deterioration in their condition over time. (icatcare.org)
Like prion diseases, Parkinson's disease and dementia with Lewy bodies result in progressive deterioration of brain functions and, ultimately, death. (sciencedaily.com)
LCA, itself a type of early onset retinitis pigmentosa, affects an estimated one out of every 30,000 - 81,000 newborns and causes progressive deterioration of the poor vision found in early childhood. (pennmedicine.org)