What is Normal pressure hydrocephalus

Normal pressure hydrocephalus (NPH) is a type of hydrocephalus. Hydrocephalus literally means ‘water in the brain’, but technically it means building up of fluid (cerebrospinal fluid) in the brain to the extent that the normally fluid-filled cavities in the brain (called ventricles) are enlarged.
Normal pressure hydrocephalus is a symptom complex characterized by the following:

  • Abnormal walking pattern (gait)
  • Urinary incontinence (unable to hold the urine)
  • Dementia (progressive intellectual decline characterised by memory loss, inability to perform normal tasks, etc.)
  • As noted above, normal pressure hydrocephalus is a disease affecting mainly the brain but leading to symptom production in other parts of the body.

    Statistics on Normal pressure hydrocephalus

    NPH is considered a rare disease based on clinical encounters. There are no exact statistical data regarding the incidence of the disease, however, it is estimated to be 5% or less as the cause of dementia.

    Risk Factors for Normal pressure hydrocephalus

    NPH is a disease of the elderly, hence increasing age is a risk factor for this disease. It usually happens after the age of 60. This must be considered in the context of dementia, which happens commonly in elderly population.

    Progression of Normal pressure hydrocephalus

    The CSF circulating the brain and spinal cord is in continuous production and absorbtion, much like recycling the water. However, in hydrocephalus, this mechanism is impaired, either due to overproduction of CSF or underabsorption of CSF.
    NPH occurs due to reduced absorption of the CSF. However, the exact mechanism of NPH is unknown.
    NPH develops insidiously. In fact, over the time the lateral ventricles (CSF filled cavity in the middle of the brain) in the brain gradually enlarge but with little increase in CSF pressure. Because of this, there is stretching and distortion of the brain tissue. Specifically, the part of the brain that is distorted contains nerve fibres that innervate the legs and bladder, hence explaining the gait and bladder problems in NPH. Dementia occurs due to distortion of the brain tissue surrounding the ventricles.

    How is Normal pressure hydrocephalus Diagnosed?

    If a patient comes in with abnormal walking gait associated with dementia, it is important find the causes. These include looking at the blood function, kidney function, liver function, thyroid function, and the body’s iron, vitamins and electrolytes level.

    Prognosis of Normal pressure hydrocephalus

    The major disability caused by NPH is progressive dementia, and it is important to recognize NPH as a cause of dementia because it is potentially treatable. While dementia caused by other diseases (such as Alzheimer’s disease and Parkinson’s disease) will take on a slowly progressive course, with treatment of NPH the dementia can be improved or even reversed.
    Considering that, the prognosis of NPH is better than other causes of dementia.

    How is Normal pressure hydrocephalus Treated?

    Surgery remains the main treatment modality for NPH. This involves directing the ventricular fluid to the abdominal cavity, called ventriculoperitoneal shunt. This procedure is done under general anaesthesia.
    Generally a tube is inserted into one lateral ventricle and attached to a cap and valve placed below the scalp. Then a tubing is tunneled underskin all the way from the valve to the tummy, and then deposited into the abdominal cavity for continuous drainage.
    The success rate of this procedure in terms of improvement of symptoms vary from 33% to more than 90% depending on the data. Complications regarding this procedure include bleeding in the brain.

    Normal pressure hydrocephalus References

    [1] Caselli, RJ. Current issues in the diagnosis and management of dementia. Semin Neurol 2003; 23:231
    [2] eMedicine: Normal pressure hydrocephalus [online]. 2004. [Cited 2005 October 25th]. Available from: URL: http://www.emedicine.com/neuro/topic277.htm#target2
    [3] Up to Date: Dementia syndromes [online]. 2004. [Cited 2005 October 25th]. Available from: URL: http://www.utdol.com/application/topic.asp?file=nuroegen/5175&type=A&selectedTitle=1~1
    [4] Vanneste J, Augustijn P, Dirven C, et al: Shunting normal pressure hydrocephalus: Do the benefits outweigh the risks? Neurology 1992; 42: 54-59
    [5] Verrees M. Management of normal pressure hydrocephalus. Am Fam Physician 2004; 70(6): 1071-8
    [6] Wikkelso, C, Andersson, H, Blomstrand, C, et al. Normal pressure hydrocephalus: Predictive value of the cerebrospinal fluid tap test. Acta Neurol Scand 1986; 73:566