NPH is one of the few causes of dementia which can be effectively treated. If a patient shows objective and subjective benefit in the external lumbar drainage test, the likelihood that their symptoms will respond to CSF shunting is very high.

The onset of dementia clearly represents a degree of irreversible damage, and consequently gait apraxia and incontinence show the most dramatic improvement after shunting. One study has reported 96% overall improvement in shunted NPH patients, but cognitive improvement was slightly less favourable at 70% (1). Other studies have reported an overall improvement in 78% of cases (2). In the small number of patients who did not show improvement, the gradual decline in function was at least halted. Comparison of outcome figures between centres is difficult, since the perceived outcome is in part related predictions made in deciding whether or not to provide a shunt. This dogma has led several groups to suggest that one of the diagnostic criteria for NPH should be improvement with CSF shunting.

In an analysis of 52 of our most recently assessed cases of NPH, 29 patients (56%) showed improvement in symptoms following external lumbar drainage. Of these, 20 patients were selected for shunting, and in all 20 patients their symptoms remained markedly improved for up to one year after the procedure (the duration of assessment). In the 9 people not given a shunt, their symptoms either remained the same or worsened.

In patients who do not show improvement following external lumbar drainage the outcome is more difficult to quantify. A certain number of patients who have strong clinical indications will be recommended for shunt procedures despite the lack of improvement on external lumbar drainage. This group represents patients who present practical difficulties in assessment, in whom the drainage test was equivocal, in whom a coincident condition, or cause of NPH clearly indicate a shunt, or in whom the severity symptoms demand an effort to treat. This group of patients overall has a much less favourable outcome.

In our recent analysis of 52 NPH patients, 25 (48%) showed no improvement with external lumbar drainage. Of these 7 people were given shunts, and 18 were left untreated. All 25 of these patients either remained the same or worsened, irrespective of whether a CSF shunt was performed. However, 19 of the patients show no further deterioration in symptoms over the following 12 months.

In summary, the external drainage test is an excellent predictor of outcome for shunt placement in NPH. Patients who test positive and proceed to have a CSF shunt fitted can expect almost complete reversal of gait apraxia and incontinence, with a strong likelihood of an improvement in cognitive function.

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References:

(1) Raftopoulos C. Deleval J. Chaskis C. Leonard A. Cantraine F. Desmyttere F. Clarysse S. Brotchi J. Cognitive recovery in idiopathic normal pressure hydrocephalus: a prospective study. Neurosurgery. 35(3):397-404; discussion 404-5, 1994 Sep.

(2) Larsson A. Wikkelso C. Bilting M. Stephensen H. Clinical parameters in 74 consecutive patients shunt operated for normal pressure hydrocephalus. Acta Neurologica Scandinavica. 84(6):475-82, 1991 Dec.

Maintained by: Andrew Beaumont MD

Department of Neurosurgery
Updated August 2003, Rev 4.0