The majority of adult hydrocephalus cases are secondary to other causes, and previously compensated congenital hydrocephalus may account for a subset of NPH, as suggested by the finding that head circumference above the 90th and 97th percentiles appears to be more common in iNPH patients than the general population. Surgical treatment is generally discouraged for patients with severe dementia, even in the setting of gait dysfunction and incontinence, regardless of radiographic findings. Although gait can improve with shunting in such patients, dementia typically does not. AD pathology is present in cortical biopsy of 75% of those iNPH patients with significant dementia at the time of shunt surgery. In patients with progressive dementia who lack gait dysfunction, a cause other than iNPH should be considered, regardless of ventriculomegaly.Д¬omorbid AD and iNPH is not uncommon, and the likelihood of each is increased with the presence of hypertension and advancing age. Early presence of cortical deficits such as aphasia, apraxia, or agnosia should raise suspicion for dementia with cortical pathology, such as AlzheimerвЂ™s disease (AD), multi-infarct dementia, or frontotemporal dementia. Depression with pseudodementia is in the differential diagnosis as well. ДЄsymmetric resting tremor, lead pipe rigidity, or visual hallucinations may suggest dementia with Lewy bodies (DLB), which causes similar cognitive deficits.

Cerebrovascular disease is comorbid in over 60% of patients with iNPH.

More global cognitive deficits can be identified in individuals with suspected iNPH, even in those with Mini-Mental Status Examination (MMSE) scores greater than 25, and the severity of cognitive deficits appears to correlate with the presence of vascular risk factors. Significant improvement in these disturbances can occur after shunting. Frontal and subcortical deficits (psychomotor slowing and impaired attention, executive, and visuospatial dysfunction) can be the earliest cognitive signs of iNPH.

Spinal tap test