Normal Pressure Hydrocephalus (NPH), a syndrome of gait dysfunction and enlarged ventricles, is one of the few causes of dementia that is potentially reversible. It is accompanied by frontal and subcortical cognitive deficits and urodynamic evidence of detrusor over-activity. Earlier trauma, mass lesions, infections, aqueductal stenosis may contribute to hydrocephalus and cause secondary forms of NPH. Disequilibrium and slowness of both upper and lower extremities are common and can improve with shunting. Appendicular tremor may be present in some cases. The bladder detrusor over-activity can result in urinary frequency and urgency in patients with idiopathic NPH (iNPH). The earlier cognitive signs of iNPH are frontal and subcortical deficits such as visuospatial dysfunction, impaired attention etc and can be improved significantly with shunting. More than 60% of individuals with iNPH also have cerebrovascular illness. Lead pipe stiffness, visual hallucinations, or an asymmetrical resting tremor are signs of dementia with Lewy bodies (DLB), which results in comparable cognitive deficits. Early signs of dementia with cortical pathologies, such as Alzheimer's disease (AD), multi-infarct dementia, or frontotemporal dementia, should arouse concern. These symptoms include aphasia, apraxia, and agnosia. It is not unusual for people with AD and iNPH to coexist, and the chances of this happening rise with age and the presence of hypertension.
A few clinical conditions such as poor venous compliance in the superior sagittal sinus, CSF pulsations, CSF absorption through arachnoid granulations, hypertensions etc are seen along with cerebrovascular disease or AD in iNPH patients. It has been suggested that an altered expression of CSF TNF-α and CSF TGF-β may regulate CSF production and absorption in relation to iNPH. The neurological symptoms include poor perfusion and interstitial edema in periventricular white matter, impaired blood flow or metabolism in vital prefrontal pathways etc and may be improved after shunting. Disturbances in basal ganglia pathways, compression of brain stem structures such as pedunculopontine nucleus can contribute to gait and cognitive dysfunction of NPH. The possibility of hereditary iNPH is unclear.
Prior shunting, a patient may be assigned to three categories: probable, possible, or unlikely iNPH. Patient’s MRI or CT must show an Evan’s index along with temporal horn enlargement, periventricular edema, periventricular signal changes, or an aqueductal/fourth ventricular flow void. In addition, clinically patient must show gait dysfunction as well as urinary/cognitive dysfunction. To meet the criteria for cognitive dysfunction, patient must have impairments in two or more domains such as fine motor speed, psychomotor speed, accuracy, attention, short term recall, executive function, or behavioural/personality change.
iNPH symptoms can be improved by CSF shunting procedures including ventriculoperitoneal, vetriculaoatrial, or ventriculopleural shunting. External lumbar drainage (ELD) is recently gaining more acceptances in patients who do not have a significant response to a spinal tap test. However, there are few associated risk complications including bacterial meningitis, headache and radiculopathy. Compared to CT, MRI is more effective in identifying periventricular white matter abnormalities.
Reference:
Shprecher, D., Schwalb, J., & Kurlan, R. (2008). Normal pressure hydrocephalus: diagnosis and treatment. Current neurology and neuroscience reports, 8(5), 371–376. https://doi.org/10.1007/s11910-008-0058-2
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