A 70 year old man comes to clinical attention with progressive memory loss, urinary incontinence, and gait instability. MRI of the brain shows dilatation of the ventricular cavities, while the cerebral coex appears normal. No infarcts are seen. Repeated lumbar punctures reveal occasional increases in cerebrospinal fluid (CSF) pressure. A biopsy of the frontal coex demonstrates the absence of neurofibrillary tangles and senile plaques. Which of the following is the most appropriate treatment?