mrcem2-1229

A 65-year-old woman comes to the clinic after a fall. You observe that she has a tremor in her left hand that is most noticeable when she is sitting and at rest. Additionally, you notice that it took her quite a while to walk towards you and unbutton her coat before sitting down. When you shake her hand, you notice that her left forearm feels stiff.
What is the SINGLE most probable diagnosis?