A 68 year old male is being investigated for falls. He also complains of
having vivid dreams that wake him up from sleep. He is impotent. On
examination you note that he has slow monotonous speech, a mask like facies,
there is a regular tremor which is more pronounced at rest, there is rigidity
of his limbs which is cogwheel in nature and his gait is slow with small steps
and lack of arm swing. Pulse 80 beats per minute regular, BP 140/80 lying,
In this patient which of the following is most likely?