A 65-year-old woman is brought to the physician by her partner due to recent behavioral changes. The symptoms began four months ago. According to the partner, the patient would be doing daily activities, such as chopping vegetables, and she would abruptly stop and appear to "blank out,” followed by resumption of the activity. Additionally, the patient recently got lost in the parking lot of a nearby grocery store that she has been visiting for many years. Past medical history is noncontributory. She does not smoke cigarettes
or consume alcohol
. Vital signs
are within normal limits. Physical examination reveals rigidity
in the bilateral upper and lower extremities. Tremors
, which began two months ago, are present in both hands at rest. Which of the following is the most likely diagnosis?