According to the article below:
“Mild cognitive impairment may occur in about 25% of PD patients… About 40% of PD patients develop dementia.” Cognitive Changes in Parkinson’s Disease J.G.Goldman 2005 AMERICAN PARKINSON DISEASE ASSOCIATION
If you google “Cognitive Impairment Parkinson’s” you’ll find more articles with varying statistics, but basically it seems fairly common.
I also found an article about impaired facial recognition in Parkinson’s.
Something funny happened to me a few years ago at a family reunion. I have loads of cousins, some of whom I had not seen since we were children (about 50 years ago!).
I was looking across the room at one guy and I remember thinking I’ll go and talk to him. Next thing I was asklng him a question and he did a double take but he answered anyway. I’m not sure how long it took me to figure out that I had already met him & asked him the same question.
Maybe a combination of not recognizing a face I’d only seen recently and dodgy short term memory
Also because of reduced movement of facial muscles in Parkinson’s you can look pretty blank sometimes and coupled with that ‘slowness of thought/difficulty initiating speech’ , people could easily get the impression that you couldn’t remember who they were.
Short-lasting episodes of prosopagnosia in Parkinson’s disease. Villa-Bonomo C, Pagonabarraga J, Martínez-Horta S, Fernandez de Bobadilla R, Garcia-Sanchez C, Campolongo A, Kulisevsky J. Parkinsonism Relat Disord. 2013 Mar;19(3):375-7.
Prosopagnosia, the selective inability to recognize known faces, has been described in Alzheimer’s disease and fronto-temporal dementia but is not expected to occur in Parkinson’s disease (PD).
We report three PD patients who developed recurrent, paroxysmal and short-lasting episodes of prosopagnosia, before progressing to PD dementia (PDD). Hallucinations and other higher-order visual deficits - such as optic ataxia and micro/macropsia - were also seen.
Progressive signs of temporal and parietal dysfunction have been suggested to herald dementia in PD. The observation of prosopagnosia and other higher-order visuoperceptive defects in the transition to dementia, reinforce the importance of posterior-cortical deficit in PD.