This patient's relatively abrupt cognitive decline with prominent executive dysfunction (eg, difficulty planning and organizing) and localizing neurologic findings (eg, asymmetric reflexes, asymmetric muscle weakness, gait disturbances) is strongly suggestive of vascular dementia (VaD) due to unrecognized stroke(s) 6 months ago.  VaD is often caused by 2 (potentially overlapping) mechanisms:

• Large artery infarction (often causing an overt stroke) produces a cortical-type VaD, in which accompanying neurologic signs/symptoms reflect the specific cortical region involved (eg, middle cerebral artery infarction causing contralateral weakness and sensory impairment).

• Small artery (ie, arteriole) infarcts can combine to cause enough cumulative damage to the brain, resulting in noticeable cognitive deficits.  Although the clinical picture is varied, a subcortical-type VaD is common because there is less arteriole collateralization in the subcortical regions compared to the cerebral cortex.  As in this patient, subcortical-type VaD is often accompanied by focal motor deficits (eg, reflex asymmetry, strength differences), abnormal gait, urinary symptoms, and psychiatric symptoms (eg, depressive syndromes).

Subcortical VaD is due to either cerebral amyloid angiopathy or, more commonly, small vessel arteriolosclerosis.  Arteriolosclerosis is common in older patients, especially those with a history of hypertension.

(Choice B)  Degeneration of the cholinergic neurons of the basal forebrain is seen in Alzheimer disease, which presents with progressive memory loss and functional impairments.  However, Alzheimer disease typically progresses gradually with early, prominent short-term memory loss, and it would not cause focal neurologic findings (eg, strength deficits, reflex asymmetry).

(Choice C)  Degeneration of dopaminergic neurons in the substantia nigra is characteristic of Parkinson disease, which can cause executive and visuospatial dysfunction with relatively mild memory impairment.  However, Parkinsonian features (eg, rigidity, resting tremor, bradykinesia) occur at least a year before the onset of dementia.

(Choice D)  Sudden acceleration-deceleration or rotational forces during blunt head injury can cause diffuse shearing of the long white matter tracts (diffuse axonal injury).  Patients have a history of acute trauma and neurologic impairment out of proportion to neuroimaging findings.

(Choice E)  Neuronal loss and atrophy of hypothalamic mamillary bodies characteristically occurs in Wernicke encephalopathy, a complication of thiamine deficiency.  Although it can cause ataxia and confusion, it also typically presents with oculomotor dysfunction (nystagmus, ophthalmoplegia), and patients typically have a history of either chronic alcohol use or malnutrition.

Educational objective:
Small artery cerebral arteriolosclerosis can lead to ischemia that predominantly affects the subcortical areas.  This can lead to vascular dementia associated with focal motor deficits, abnormal gait, urinary symptoms, and psychiatric symptoms.