Final answer:
The patient's symptoms may indicate orthostatic hypotension and a form of parkinsonism such as Parkinson's disease, Multiple System Atrophy, or Lewy Body Dementia. Haloperidol's side effects on motor control should also be considered, as it affects regions like the basal ganglia. Accurate diagnosis requires a neurologist's assessment, including brain scans and medication review.
Step-by-step explanation:
The 75-year-old patient's presentation of mild intermittent forgetfulness, hallucinations, delusions, and confusion, along with frequent falls and significant differences in blood pressure when lying down versus standing, suggests a condition known as orthostatic hypotension. This can occur when the blood pressure drops significantly upon standing due to insufficient autonomic response, causing dizziness and potential falls. The bilateral limb and axial rigidity without tremor, as well as the cognitive and psychological symptoms, may indicate a form of parkinsonism, such as Parkinson's disease (PD) or one of the Parkinson's plus syndromes, like Multiple System Atrophy (MSA) or Lewy Body Dementia (LBD).
Given that the usual causes like stroke, Parkinson's disease, diabetes, or thyroid dysfunction have been ruled out and medication-related causes are suspected, the side effects of certain medications, such as haloperidol, should be considered. Haloperidol can cause motor control changes due to its impact on the regions of the nervous system that control movements, particularly the basal ganglia.
Overall, the combination of motor and non-motor symptoms strongly suggests a neurodegenerative condition which should be thoroughly investigated by a neurologist. Tests such as brain scans and careful review of medications should be conducted to reach an accurate diagnosis and to manage the patient's symptoms effectively.