Key messages
- Surgery to move excessive fluid away from the brain (cerebrospinal fluid (CSF)-shunting) likely improves walking speed and disability in the short term (less than six months post-surgery) in people with idiopathic normal pressure hydrocephalus (iNPH).
- CSF-shunting did not cause any deaths, and repeat surgery was rare, but unwanted effects were common in the studies assessed.
- More evidence on the effect of CSF-shunting on quality of life is needed.
What is idiopathic normal pressure hydrocephalus?
Normal pressure hydrocephalus (NPH) is a medical condition where normal fluid-filled brain structures (ventricles) slowly become larger over time (hydrocephalus), and the surrounding brain structures slowly change to adjust to this. Eventually, the critical brain structures become affected, causing symptoms such as difficulty walking, thinking, and with bladder control. Sometimes there is a clear reason for the ventricles getting larger, for example after a head injury, where blood can 'clog-up' the ventricles. However, in older adults (over 60 years), NPH develops with no clear cause, known as 'idiopathic' normal pressure hydrocephalus (iNPH).
What did we want to find out?
Since 1965 there have been reports of patients with iNPH getting better when an operation is performed where a tube is inserted into the brain or spinal canal to move the cerebrospinal fluid (CSF) to an area of lower pressure such as the abdominal cavity or right atrium of the heart (CSF-shunting). However, most of the evidence to support the use of CSF-shunting has been of low quality, and people having CSF-shunting were not directly compared with control groups who did not have CSF-shunting. As such, medical practitioners differ in opinion about the benefit of CSF-shunt surgery for iNPH. We wanted to compare the existing high-quality studies to find out if there was evidence showing that CSF-shunting improved walking (gait), disability, cognitive function (thinking), urinary function, and quality of life. We also wanted to know if CSF-shunting was associated with any unwanted effects.
What did we do?
We searched for and compared all studies in which people with NPH were assigned randomly to CSF-shunting or to a control group which was either delayed CSF-shunting or CSF-shunt surgery where the shunt was temporarily set to 'inactive' mode. We included only people with NPH who had problems walking, thinking, or with bladder function and no clear cause for their hydrocephalus (iNPH).
What did we find?
We included four studies in the review, but could only use data from three in the analysis. One larger study was from Japan, and three smaller studies were from Sweden, the UK, and a US-Canadian-Swedish collaboration. All studies included only iNPH patients (average age 75 years) who had difficulty walking with or without problems with thinking and bladder control. People were observed for 6 to 12 months. The included studies involved a total of 140 participants (73 who had active/immediate CSF-shunting and 67 controls).
What are the conclusions?
Walking speed probably improves with CSF-shunting compared with control. CSF-shunting may improve walking function by an uncertain amount. CSF-shunting probably results in a large improvement in patient disability. Only 3.4 participants needed to have CSF-shunting to result in 1 being functionally independent (able to perform activities of daily living). It is unclear if CSF-shunt surgery has an effect on cognitive function or unwanted effects. There was no information regarding how CSF-shunting affects quality of life.
What are the limitations of the evidence?
Our confidence in the results for walking speed and patient disability is moderate. Our confidence in the other results is low to very low. The included studies were very small, which means that more studies are needed to increase our confidence in the evidence. Due to the design of the studies we assessed, there was little information about unwanted effects occurring with CSF-shunting compared to no surgery at all. In participants who had CSF-shunt surgery, 52% had an unwanted effect of any kind, but the need for repeat surgery after having a shunt was infrequent (8.9%), and there were no deaths that were clearly related to CSF-shunt surgery. Strokes occurred more commonly than expected in the 12 months following shunt surgery (8%); more research is needed to confirm this finding.
How up-to-date is this evidence?
The evidence is current to February 2023.
We found moderate-certainty evidence that CSF-shunting likely improves gait speed and disability in iNPH in the relative short term. The evidence is very uncertain regarding cognition and adverse events. There were no longer-term RCT data for any of our prespecified outcomes. More studies are required to improve the certainty of these findings. In addition, more information is required regarding patient ethnicity and the effect of CSF-shunting on quality of life.
Normal pressure hydrocephalus (NPH) occurs when the brain ventricles expand, causing a triad of gait, cognitive, and urinary impairment. It can occur after a clear brain injury such as trauma, but can also occur without a clear cause (termed idiopathic, or iNPH). Non-randomised studies have shown a benefit from surgically diverting ventricular fluid to an area of lower pressure by cerebrospinal fluid (CSF)-shunting in iNPH, but historically there have been limited randomised controlled trial (RCT) data to confirm this.
To determine the effect of CSF-shunting versus no CSF-shunting in people with iNPH and the frequency of adverse effects of CSF-shunting in iNPH.
We searched the Cochrane Dementia and Cognitive Improvement Group's register, Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid SP), Embase (Ovid SP), PsycINFO (Ovid SP), CINAHL (EBSCOhost), Web of Science Core Collection (Clarivate), LILACS (BIREME), ClinicalTrials.gov, and the World Health Organization International Clinical Trials Registry Platform on 15 February 2023.
We included only RCTs of people who had symptoms of gait, cognitive, or urinary impairment with communicating hydrocephalus (Evans index of > 0.3) and normal CSF pressure. Control groups included those with no CSF shunts or those with CSF shunts that were in 'inactive' mode.
We used standard Cochrane methodological procedures. Where necessary, we contacted study authors requesting data not provided in the papers. We assessed the overall certainty of the evidence using GRADE.
We included four RCTs, of which three were combined in a meta-analysis. The four RCTs included 140 participants (73 with immediate CSF-shunting and 67 controls who had delayed CSF-shunting) with an average age of 75 years. Risk of bias was low in all parallel-group outcomes evaluated apart from gait speed, cognitive function (general cognition and Symbol Digit Test) (some concerns) and adverse events, which were not blind-assessed. CSF-shunting probably improves gait speed at less than six months post-surgery (standardised mean difference (SMD) 0.62, 95% confidence interval (CI) 0.24 to 0.99; 3 studies, 116 participants; moderate-certainty evidence). CSF-shunting may improve qualitative gait function at less than six months post-surgery by an uncertain amount (1 study, 88 participants; low-certainty evidence). CSF-shunting probably results in a large reduction of disability at less than six months post-surgery (risk ratio 2.08, 95% CI 1.31 to 3.31; 3 studies, 118 participants; moderate-certainty evidence). The evidence is very uncertain about the effect of CSF-shunting on cognitive function at less than six months post-CSF-shunt surgery (SMD 0.35, 95% CI −0.04 to 0.74; 2 studies, 104 participants; very low-certainty evidence). The evidence is also very uncertain about the effect of CSF-shunt surgery on adverse events (1 study, 88 participants; very low-certainty evidence). There were no data regarding the effect of CSF-shunting on quality of life.