Medical correspondent checking after a long day of toddler-wrangling.
Not a neurologist. No specialist knowledge. BUT yes, dopamine is reduced in parts of the brain in Parkinson's disease AND in CBD but my understanding (which is incomplete!) is that giving dopamine treament can help in Parkinson's, but not in CBD.
I've no idea re dopamine, ADHD etc. I think an experienced neurologist would be pretty unlikely to mistake ADHD for a rare but very well recognised terminal neurological disease!
Saccadic eye movement such as mentioned in the clinic letter can be normal to a small degree and in some circumstances. Abnormal patterns of them are linked to the possibility of various illnesses (etc). This can be very subtle and you'd really need to be an expert to pick up the variations (and I am not an expert!)
How often do people fake neurological signs? It certainly happens, I've seen it happen in my own consulting room. But also, functional neurological disease is not uncommon - and people are not then consciously faking symptoms, but symptoms are more likely to be a sign of subcoscious turmoil and often don't follow typical well-recognised patterns of disease.
But faking neuro symptoms - ie, making up a story and saying that you have numbness, or weakness, or some sort of sensory loss -- I'm sure that is far from uncommon. No-one can get inside you and know what you're really feeling so you can say what you like! Again, a neurologist's skill will be to marry the symptoms (ie what the patients says) with the signs (ie any abnormalities that can be found when the patient is examined).
There is no proof whatsoever (that I'm aware of, from the letters) that there was any suggestion of TW faking anything when he saw the neurologist.
Something else I want to say, but in a different vein, so I'll start a new posting.