J.F. is a 72-year-old woman who was diagnosed with mild cognitive impairment 6 months ago. She had..

J.F. is a 72-year-old woman who was diagnosed with mild cognitive impairment 6 months ago. She had been increasingly forgetful and confused for about 1 year before the diagnosis. Approximately 3 months ago, J.F. and her family decided that J.F. should move in with them so she would not be left alone. Since moving in with the family, her son has noted that she seems “spaced out” at times. Some days, she appears to be very clear and not confused; other days she is very forgetful and requires assistance with daily tasks. Her daughter-in-law reported that J.F. has been unsteady on her feet at times and has fallen twice. She notes at times she moves very slowly and has difficulty initiating movement. Recently, J.F. reported seeing people coming out of the painting on the wall (a European street scene), stating that “they were walking all through the house trying to steal anything that can be hidden in a coat pocket.” At the physician visit, J.F. was found to be medically stable. Vital signs, serum chemistries, and complete blood cell count were within normal limits. Her MMSE score was 21/30. During the review of systems, J.F.’s daughter-in-law had to answer some questions because J.F. appeared either not to hear them or to ignore them. On physical examination, she demonstrated mild cog-wheeling rigidity bilaterally, bradykinesia, and masked facies; she did not display a resting tremor. What is the most likely explanation for J.F.’s presentation?