Some patients develop dementia as the disease progresses. As antiparkinsonian therapy can worsen confusion and hallucinations, the presence of cognitive dysfunction can also limit administration of medication to improve motor symptoms. By ten to twelve years into therapy, many patients have developed balance difficulty. This is another important milestone. True postural imbalance is not improved by any current antiparkinsonian therapy.
Patients are then at risk for morbidity and mortality from falls.
Individual progression varies greatly. Some patients maintain relatively good function fifteen years into the disease and others experience meaningful disability within a few years.