Normal Pressure Hydrocephalus – September 2017
On Tuesday September 5th 2017, Queen Square Private Healthcare hosted a seminar with Mr Ahmed Toma, a consultant neurosurgeon at the National Hospital for Neurology and Neurosurgery in Queen Square. This event aimed to provide the audience of GP’s and other healthcare professionals with a guide to the diagnosis and management of patients with normal pressure hydrocephalus (NPH), with particular consideration paid to the elderly patient.
Mr Toma began his presentation by explaining that normal pressure hydrocephalus is an adult-onset syndrome, typically associated with a classic triad of clinical presentations:
- Gait/balance disturbance
He explained that NPH is most often associated with a so called ‘classic magnetic gait’, where a patient will often have a wide based, shuffling gait. Patients will often freeze and then experience difficulty in re-initiating.
- Cognitive impairment
Frontal lobe subcortical processes are most commonly effected in NPH. Patients will present with forgetfulness, inertia, inattention and decreased speed of complex information processing. Memory problems are usually a component of the overall syndrome and can even be predominant. Mr Toma explained that this may lead to a misdiagnosis of Alzheimer’s disease. However, he explained that impairment of memory and orientation is most commonly disproportionately mild compared with AD. Most crucially, Mr Toma reminds the audience that cognitive impairment in NPH can be classed as a curable dementia.
- Urinary dysfunction
Mr Toma explained that urinary symptoms in NPH are typically increased frequency and urgency, although gait disturbance can result in functional incontinence. Frank urinary incontinence is usually associated with disease progression and in the most severe cases, incontinence may be associated with lack of concern for micturition, due to frontal lobe impairment.
There are two types of NPH:
- Secondary – due to subarachnoid haemorrhage, trauma, tumour, infection or surgical complication.
Population based studies have shown an incidence of approximately 5.5 patients per 100,000 per year, with a peak onset in the seventh and eighth decades of life.
NPH is often misdiagnosed as Parkinson’s disease, Alzheimer’s disease or dementia, due to its chronic nature and often non-specific presenting symptoms
Mr Toma explained that the clinical syndrome of NPH, first described in the New England Journal of Medicine as a treatable condition in 1965, is caused by the non-obstructive enlargement of the cerebral ventricles – cavities within the brain parenchyma that are filled with cerebrospinal fluid (CSF). CSF bathes and cushions the brain and spinal cord, protecting these important organs from impact, providing buoyancy against the effect of gravity and providing chemical stability by supplying crucial nutrients.
The clinical syndromes associated with hydrocephalus are caused by an increase in intracranial pressure due to the abnormal expansion of the ventricles of the brain as CSF accumulates. In NPH, this intracranial pressure gradually falls but still remains slightly elevated and the CSF pressure reaches a high normal level. Therefore, in NPH, measurement of intracranial pressure is usually not elevated and as a result, patients do not exhibit the classic signs that accompany raised intracranial pressure i.e. headache, nausea, vomiting or altered consciousness. Mr Toma explained (following a question from the audience) that the pressure placed on adjacent cortical tissue by the enlarged ventricles in NPH is responsible for the classic symptom triad described above (first described by Hakim and Adams in 1965).
Mr Toma explained that the pathophysiology of NPH is debated, although various studies have shown that patients with NPH typically have more vascular risk factors, and it has been suggested that NPH could be regarded as a subtype of vascular dementia. This association has led many clinicians to have most confidence in pulse wave encephalopathy as a possible explanation for NPH.
Pulse Wave Encephalopathy (Windkessel Effect)
Mr Toma explained that the cranium is essentially a closed box filled with incompressible tissue or fluid. During systole, the increase in volume of the arteries within the cranium causes an increase in intracranial pressure, exerting pressure on the CSF within the subarachnoid spaces and venous structures. It has been identified that in patients with vascular risk factors, the normal elastic expansion of arterial walls is reduced. The consequence of this is that blood flow has a more pulsatile, rather than smooth laminar flow characteristic, since more of the force exerted from the heart during systole is transmitted to blood flow, rather than the elastic expansion of arterial walls. It is this increased pulsatility of the choroid plexus arteries in particular, and the associated pulsation of the ventricular CSF that is deemed responsible for ventricular enlargement in NPH.
Mr Toma explained that this theory is supported by the typical imaging appearances associated with NPH, the most common being that of disproportionately enlarged subarachnoid-space hydrocephalus (DESH).
Figure 1. – A Coronal T1 MRI Brain image showing DESH.
As shown in figure 1, radiological appearances in the context of normal pressure hydrocephalus are characterised by disproportionately enlarged subarachnoid spaces (note the enlarged sylvian fissures (green arrows) and cerebral ventricles), compared to relatively narrow subarachnoid spaces towards the high convexity.
Figure 2. – A Coronal T2 MRI Brain image showing obstructive hydrocephalus (secondary to tumour).
In comparison, the T2 weighted MRI image in figure 2 (an example of an obstructive hydrocephalus) shows enlarged cerebral ventricles but with global narrowing of all subarachnoid spaces due to raised intracranial pressure.
Currently, the only treatment for NPH is surgical, where relief may be gained by the surgical implantation of a ventriculoperitoneal shunt (VP) or a lumboperitoneal shunt (LP) to drain excess CSF to the abdomen where it is absorbed. Various valves can be fitted to the shunt tubing to provide control over the rate of drainage of CSF, and Mr Toma explained that a ProGav valve is most commonly used in Queen Square. This valve can be set manually, has an anti-gravity component to prevent over drainage with changes in posture, and is also safe for MRI scanning. Mr Toma explained that shunting is regarded to be a relatively low risk operation which has the potential to create significant clinical improvement. Whilst response to shunting varies between studies, it has been shown in Queen Square that using low opening pressures with valve systems has been shown to increase clinical improvement, whilst not increasing complication rates. Following a question from the audience, he also stated that a VP shunt would typically be used in elderly patients over an LP shunt, in order to reduce the risk of over drainage and complicating subdural haematoma.
The workup for the shunting procedure will typically involve imaging and then lumbar puncture (when CSF opening pressures can be measured) and a lumbar tap test. A clinical improvement following the removal of CSF during a tap test carries a high predictive value for subsequent success with shunting. In Queen Square, a temporary lumbar drain is often used, which carries the highest sensitivity and specify with regards to predicting successful outcome following shunting. Mr Toma showed the audience a number of video case studies which showed significant improvement in gait and cognition in a number of patients who had undergone lumbar tap test.
Intracranial pressure monitoring and a CSF infusion test (where the outflow conductance of CSF can be measured) may also be used, but are not yet common practice.
Mr Toma explained that shunting should be considered as an early intervention. The surgery is associated with low mortality and although the revision rate (due to shunt blockage and breakage) is relatively high, revision always creates an improvement following deterioration. There is no age limit to the procedure as complications are rare, and outcomes are similar regardless of patient age. Early intervention has been shown to produce the best outcomes and various studies have shown that shunting is a cost effective procedure, producing a good economic benefit in the long term.
Mr Toma explained that most importantly, the benefit from shunting of patients with NPH is not temporary. Patients often describe a significant improvement in quality of life, and in studies of patient satisfaction following shunting, even those patients who had a limited improvement reported high levels of satisfaction, since there really is no other treatment that carries any significant chance of improvement.
At the end of a highly engaging talk, Mr Toma summarised with the following take home messages:
- NPH is an adult onset syndrome, and clinical suspicion should be high in patients displaying the classic presenting symptoms who are in their 70’s and 80’s.
- Clinical presentation is often the classic triad of symptoms of Gait/balance disturbance, cognitive impairment and urinary dysfunction. Whilst these symptoms may appear non-specific, there are differentiating features which make it possible in some cases to rule out other diagnosis. If in doubt, Mr Toma recommended referral to neurology or neurosurgery so that NPH can be investigated and, if necessary, treated early.
- Symptoms of NPH can be improved with CSF shunt surgery. This surgery carries low risk of complication, and can improve quality of life for sufferers. The treatment carries a good economic benefit, particularly in view of the increasingly ages population within the UK.
For further information on this topic, or to contact Mr Toma to discuss a referral, please contact his secretary Molly Truss at firstname.lastname@example.org, or 0203 448 8948.
The final Queen Square GP Seminar of 2017 will be held on November 29th, when Dr Tabish Saifee will be discussing Parkinson’s disease and other movement disorders. Registration is now open.