An older adult patient is brought to the emergency room by her family. They report that over the past two days, she has been increasingly disoriented and confused, especially at night. Her condition seems to fluctuate throughout the day, with periods of relative lucidity. She is also easily distractible and has had difficulty recognizing family members. Her medical history includes hypertension and type 2 diabetes. There is no history of any recent head injury or known neurological disorders. Based on the clinical scenario, what type of altered mental status is most likely present in this patient?
a. Chronic cognitive impairment, consistent with Parkinson dementia
b. Progressive dementia, consistent with Alzheimer disease or similar disorder
c. Acute onset, fluctuating course of cognitive impairment, consistent with delirium
d. Chronic neurological disorder, consistent with vascular dementia