Large-volume lumbar puncture is indicated in this patient with likely normal pressure hydrocephalus (NPH). NPH is the most likely diagnosis in the setting of the triad of gait abnormalities, cognitive impairment, and urinary disturbance, especially when neuroimaging studies show enlarged ventricles out of proportion to cortical atrophy. NPH is a potentially reversible cause of cognitive and motor decline. A large-volume lumbar puncture with measurement of intracranial pressure and removal of 30 to 50 mL of cerebrospinal fluid (CSF) should be performed before consideration of placement of a ventriculoperitoneal shunt. Cognitive, balance, and gait examinations before and after the lumbar puncture can be useful to evaluate for potential response to shunting. If a positive response to the initial lumbar puncture is not seen and the clinical suspicion remains high, serial lumbar punctures or continuous lumbar drainage can be considered.

Periventricular white matter changes can be seen on the brain MRI and may have an identical appearance to what is seen in small-vessel vascular disease. However, without additional clinical or neuroradiologic evidence of a previous infarction, extensive evaluation with neurovascular imaging to assess for a cause of these radiologic changes on brain MRI is not warranted. Periventricular hyperintensities are a frequent finding in normal pressure hydrocephalus and are thought to be related to transependymal resorption of CSF.

The cholinesterase inhibitor donepezil is sometimes effective in improving cognitive symptoms and function in patients with Alzheimer disease but has no benefit for the gait and cognitive disturbances typical of normal pressure hydrocephalus.

Although this patient has evidence of lower-body parkinsonism, he lacks other findings that suggest the presence of idiopathic Parkinson disease, such as a resting tremor, asymmetric onset of motor symptoms, and typical nonmotor symptoms. Therefore, levodopa is not likely to result in any symptomatic benefit.