Idiopathic normal pressure hydrocephalus--overviews and pathogenesis

Idiopathic normal pressure hydrocephalus (iNPH) is a syndrome of gait disturbance, dementia and urinary incontinence without any preceding disorders in elderly patients. Rapid increase of elderly population in Japan prompted us to make guidelines for diagnosis and management of iNPH. The Japanese guidelines were published in 2004 and their characteristics were summarized as follows; 1) Simple and treatment-oriented, 2) Three diagnostic levels: possible, probable and (definite); Shunt surgery is indicated for probable iNPH only, 3) Clinical significance of gait disturbance as the most frequent and treatable symptom, 4) CSF tap test as a keystep of diagnosis, 5) Recommend the use of a programmable valve for prevention of overdrainage, and 6) Flow-charts for diagnosis, shunt indication and prevention of shunt complication. The International guidelines of iNPH were published in 2005. They were created based on evidence-based medicine, but there are some differences. Major differences were in the concept of iNPH, age, range of CSF pressure, MRI findings, and evaluation of CSF tap test, outflow resistance measurement and continuous CSF drainage. This difference would be derived from the weight of the accuracy, popularity and invasiveness of diagnostic tests. At present the pathogenesis of iNPH is not known. A new proposal in which CSF is mainly absorbed in the capillaries in all of the central nervous system may contribute to clarify the pathogenesis in iNPH.