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Natural history of idiopathic normal-pressure hydrocephalus

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Abstract

Natural history of idiopathic normal-pressure hydrocephalus (INPH) is not clear. We performed a literature search for studies that looked into the outcome of unshunted INPH patients trying to answer the following questions: Do all INPH patients deteriorate without shunt? If yes, at what rate? Do some NPH patients improve without shunt? If yes, to what extent? Six studies objectively described the outcome of 102 INPH patients. Result shows that without surgery, most INPH patients had measurable deterioration as early as 3 months following initial assessment. A small number of patients might improve without shunt, however the extent of improvement is not clear. The homogeneity of the findings of the cohort studies provided high evidence supporting the rule of shunt surgery in INPH patients.

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Disclosure

Clinical research fellow at Victor Horsley Department of Neurosurgery (Mr Toma) is supported by a grant from B. Braun/Aesculap.

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Authors and Affiliations

  1. Victor Horsley Department of Neurosurgery, National Hospital for Neurology and Neurosurgery, Queen Square, London, UK

    Ahmed K. Toma, Neil D. Kitchen & Laurence D. Watkins

  2. Academic Neurosurgery Unit, St George’s University of London, London, UK

    Simon Stapleton & Marios C. Papadopoulos

Authors
  1. Ahmed K. Toma
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  2. Simon Stapleton
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  3. Marios C. Papadopoulos
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  4. Neil D. Kitchen
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  5. Laurence D. Watkins
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Correspondence to Ahmed K. Toma.

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Comments

Ernst Delwel, Rotterdam, The Netherlands

The authors have performed a literature search for studies that looked into the outcome of unshunted patients who were diagnosed as idiopathic normal-pressure hydrocephalus (INPH).

The authors state that based on different inclusion criteria, the overall improvement rate after shunting is 45–60%. This means that the not-improved patients had another disease mimicking INPH or the patients were already in the phase of irreversibility, for instance because of a delay in treatment. Of course, shunt dysfunction should always be ruled out.

So if a group of patients suspected of INPH without a shunt are followed, it depends on the inclusion criteria for INPH what the result will be. In case of very strict and limiting criteria and implementation of the extended lumbar drainage with its very high positive predictive value, the chance of improvement is expected to be very high. However, in case of liberal inclusion criteria, the chance of postoperative improvement for the whole group is expected to be much lower.

In the first case, one would expect that most patients will more likely show the disease course of real INPH patients. In the second case however, one would expect more INPH-mimicking diseases included like (vascular) dementia, Parkinson, depression, etc. In this group the expected disease course during follow-up is expected to be less predictable and more heterogeneous. In the second case, one would expect very slow progression in some cases, stable disease in other cases and sometimes even temporary improvement dependent on the real pathology.

In other words, the best group to study the natural history of INPH is the group in which very strict inclusion criteria are used and in which the decision to include is based on a test or a combination of tests with a very high positive predictive value, like extended lumbar drainage for a couple of days [1].

The six studies that were presented used different inclusion criteria. Only one cohort study of Razay et al. [2] compared two groups without applying any further factors, while the other five cohort studies compared two groups depending on the results of prognostic tests. So in the last five cohort studies, the unshunted group that was followed was less likely to have INPH and the natural history of the groups in these five cohorts might particularly reflect the natural history of INPH-mimicking diseases. In the study of Razay et al. [2], inclusion criteria were mild cognitive impairment or dementia and/or gait disorders and enlarged ventricles on brain imaging. These are rather liberal criteria which might have lead to inclusion of relatively more patients who have no real INPH which is the drawback of their study. Despite differences in inclusion criteria, confounding elements and bias in the presented studies, it is obvious that most not-shunted patients will deteriorate within the period of 3 months after initial assessment, which is a valid and useful conclusion.

A prospective randomized study on a shunted and a not-shunted group of INPH patients, in which very strict and limited inclusion criteria and tests with a high positive predictive value are used, would be needed in search of a more valuable answer to the question what the natural history of INPH really is.

References

1. Haan J, Thomeer RTWM (1988) Predictive value of temporary external lumbar drainage in normal pressure hydrocephalus. Neurosurgery 22:388–391

2. Razay G, Vreugdenhil A, Liddell J (2009) A prospective study of ventriculo-peritoneal shunting for idiopathic normal pressure hydrocephalus. J Clin Neurosci 16:1180–1183

Siamak Asgari, Ingolstadt, Germany

The authors present a review of the literature with selection of reported patients with suspect of idiopathic normal-pressure hydrocephalus (NPH), who did not undergo CSF shunting. The authors wanted to get evidence-based analysis of the spontaneous course of NPH without surgical therapy. They could summarize 102 patients from totally six studies. During a follow-up time from 3 months to 7 years, nearly 50% of patients remained clinically unchanged and the other 50% of patients showed deterioration. However, this paper corroborates the effectiveness of shunt procedures in NPH. The impact of this paper would be higher if it would focus on the untreated patients. Detailed informations of the patients in the follow-up are necessary. What kind of psychological and neurological tests were used for measuring the patient’s functions? A graphic illustration showing clinical deterioration or status over the follow-up period would be of great help. Finally, a comment to newer strategies in the treatment of NPH like endoscopic third ventriculostomy should be mentioned.

Veit Rohde, Göttingen, Germany

The authors performed a literature research to define the natural history of idiopathic NPH (iNPH). They identified six studies with a total number of 102 patients. In two of these studies, outcome after ventriculoperitoneal shunt was compared with that in patients who either refused surgery or are on the waiting list (23 patients). In the remaining four studies, outcome after ventriculoperitoneal shunt was compared with that of patients who were considered to be no good candidates for shunting according to diagnostic tests. To take the worst case scenario, none of these patients are iNPH patients, which would mean that the conclusions which are drawn by the authors are only based on the findings in 23 patients.

Nonetheless the findings in these 23 untreated patients with worsening of at least one of the components of the Hakim triad or worsening in global tests within 24 months in all of them are striking and indicate that the outcome of iNPH without shunt is poor. This especially holds true, because the assumption that none of the remaining patients in whom shunt surgery was not considered to be indicated has an iNPH possibly is too puristic.

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Toma, A.K., Stapleton, S., Papadopoulos, M.C. et al. Natural history of idiopathic normal-pressure hydrocephalus. Neurosurg Rev 34, 433–439 (2011). https://doi.org/10.1007/s10143-011-0316-7

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