What is idiopathic in normal pressure hydrocephalus?

Area of Science:

• Neurology
• Neurosurgery
• Neuroscience

Background:

• Idiopathic normal pressure hydrocephalus (iNPH) is a condition with unclear causes, often debated in medical literature.
• Acquired causes include subarachnoid hemorrhage, meningitis, and trauma, while iNPH has no identifiable cause.

Purpose of the Study:

• To review the causes of iNPH, focusing on its relationship with neurodegenerative diseases.
• To present a unified model for iNPH pathogenesis based on current evidence.

Main Methods:

• A literature search was conducted on PubMed using keywords related to hydrocephalus, neurodegeneration, and cerebrospinal fluid.
• The review synthesized findings on genetic factors, cilia function, and the glymphatic system in iNPH.

Main Results:

• Recent research identified monogenic forms of iNPH linked to cilia genes and highlighted the role of the glymphatic system.
• Four potential relationships between iNPH and neurodegeneration were explored: coincidental, iNPH predisposing to neurodegeneration, neurodegeneration predisposing to iNPH, or independent processes.
• A unified model proposes three sequential events: impaired CSF dynamics, reversible signs, and irreversible signs.

Conclusions:

• iNPH is a syndrome with diverse pathogenetic mechanisms, not solely a cerebrospinal fluid (CSF) disorder.
• The condition is recognized as a brain disorder manifesting with ventriculomegaly.
• Understanding iNPH mechanisms supports renaming it "Hakim's disease."