A 72 year old man is brought in after his family found him wandering in the streets, 2 days after leaving home to visit a friend.
He was diagnosed with Parkinson's disease 1 year ago, for which he is currently under treatment with carbidopa 50 mg and levodopa 200 mg four times a day. Despite treatment, his Parkinsonian symptoms have not improved significantly.
He began experiencing urinary incontinence and visual hallucinations 4 months ago. He was started on haloperidol to control the latter, only to be discontinued soon afterwards, due to worsening of the Parkinsonian symptoms.
He has been exceptionally absent-minded and accident prone (with frequent falls) for years. These were initially put down to stress, but lately he has become increasingly forgetful, which his wife sees as unusual, even for him.
His medical and family histories are otherwise unremarkable. He drinks socially but does not smoke or abuse recreational drugs.
A recent thyroid function profile was normal, as were serum vitamin B12 levels.