Systematic Review
Treatment and clinical outcome in patients with idiopathic normal pressure hydrocephalus – a systematic review
1. okt. 2014
15 min.
Faktaboks
Fakta
The term normal pressure hydrocephalus (NPH) was initially introduced by Adams and Hakims in 1965. NPH is typically characterised by the clinical triad of abnormal gait, urinary incontinence and dementia, accompanied by normal cerebrospinal fluid (CSF) pressure on lumbar puncture and the absence of papillary oedema [1]. NPH can be divided into two main categories: idiopathic normal pressure hydrocephalus (iNPH) and secondary NPH. Secondary NPH can be caused by traumatic head injury, subarachnoid haemorrhage, infections and tumours. The syndrome of iNPH most commonly manifests in the sixth or seventh decade of life [2], and is one of the few potentially reversible causes of dementia, gait disturbance and urinary incontinence. It is therefore important to establish the correct diagnosis [3-5]. In elderly, the symptoms may resemble other causes of dementia including Parkinson’s disease, which can cause problems when diagnosing these patients. Currently, there is no standardised means of diagnosing iNPH or of identifying the candidates in whom surgery would be beneficial. It is therefore difficult to give an exact incidence estimate for iNPH. Studies suggest an incidence range of iNPH from 0.7 to 5.5 per 100,000 persons [6, 7].
Prognostic tests like the CSF tap test, the lumbar infusion test and intracranial pressure (ICP) monitoring have made it easier to identify the patients who will most likely benefit from surgery. The cause of iNPH has not yet been fully established, but several mechanisms regarding its pathophysiology have been suggested. Ventricular dilatation on computed tomography (CT)/magnetic resonance imaging (MRI) is a characteristic, but not a specific sign of iNPH and is thought to be due to defective CSF absorption and stagnation of the CSF flow [8, 9]. Among the recently suggested mechanisms, various authors have highlighted a new theory concerning the morphological changes in iNPH patients’ brains. The theory proposes that malfunction of arachnoid granulations causes a decreased subarachnoid space and thereby alters CSF absorption [7, 9-11)]. Another theory is that diverse cephalic degenerative changes may impair CSF absorption [3, 12].
The gold standard in treatment is shunting [13-17], but more recent studies have suggested a positive effect of endoscopic third ventriculostomy (ETV) [8, 9, 16-19].
The purpose of this review was to provide an overview of the current literature investigating the treatment and outcome in iNPH patients.
METHODS
Search strategy
We performed a literature search in accordance with the preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement [18].
The clinical question posed was: does diagnostics and treatment of patients with idiopathic normal pressure hydrocephalus affect the outcome and prognosis in a positive matter?
A PubMed search on publications from 1990 to 2012 was performed (Figure 1) in September 2013. Search words were normal pressure hydrocephalus, iNPH, treatment, therapy, and outcome.
Selection criteria and study eligibility
Titles were examined by both authors (LT and VB). Titles that were not relevant were excluded after both authors had examined the abstracts. Any studies of interest to the systematic review were included. The selected full papers were individually studied by both authors. Articles concerning iNPH and articles discussing diagnostics, treatment and outcome were included.
Risk of bias in individual studies
The studies were selected carefully with a focus on biases concerning the authors’ possible economic and personal interests.
RESULTS
The PubMed search returned a total of 430 articles. After excluding articles that did not fulfil our criteria, we were left with 43 articles to screen. Ten articles were excluded. Ten articles were included from reference lists. The eliminated articles did not match our clinical question properly.
The inclusion criteria were patients diagnosed with NPH, articles discussing treatment and outcome, and articles of a newer date.
Some only discussed NPH in general, and not the iNPH subgroup. Finally, some articles were excluded due to selection bias, including financial interests. The final result was therefore 43 articles. These studies were both retrospective and prospective. Approximately 40% were prospective (Figure 1).
Clinical symptoms before shunting
The classic triad of iNPH includes gait disturbance, cognitive impairment and urinary incontinence. These symptoms vary in severity and appearance. Gait impairment is the most common clinical feature in iNPH, with a frequency ranging from 80% to 100%. Gait disturbance is often the patient’s initial complaint. The second most frequent symptom is cognitive impairment, which ranges from 42% to 100%. Urinary incontinence ranges from 34% to 82%. The full clinical triad is present in 38-82% of cases [4, 5, 7, 8, 10, 13, 20-25]. The gait is described variably, but is most often characterised by a slow and magnetic gait as if the patients’ feet were stuck to the ground. Initiating movement is problematic and the walk is unsteady [22, 23].
Gait disturbance is the clinical symptom most likely to respond to surgery [10, 13, 19, 26, 27].
Instability and balance problems during walking were reported to be an element of poor outcome from shunting in one study [7], whereas another study found that balance dysfunction before shunting was associated with a better outcome after surgery [5].
The cognitive deficits observed in these patients comprise loss of subcortical and frontal functions, including memory decline, impaired attention and general mental sluggishness. The cognitive deficits make Alzheimer’s disease and other causes of dementia important and common differential diagnoses. It is difficult to distinguish iNPH from other types of dementia, but it is crucial as only symptoms related to iNPH will improve from surgery. The cognitive impairment in iNPH does, however, not usually include aphasia, apraxia or agnosia [27]. Through neuropsychological testing, deficits in attention, executive function, visuoperceptual and visuospatial functions have been found to be more severe in patients with iNPH than in patients with Alzheimer’s disease [28].
Urinary incontinence is the least prominent symptom, and usually a late sign of the disease [29]. This is partly due to the pathophysiology of iNPH, but it is also evident that a prominent gait disturbance may contribute to problems getting to the toilet in time. Severe cognitive deficits and the presence of urinary incontinence are associated with a poor prognosis [7, 15, 25, 29, 30]. It has been discussed whether the duration of the symptoms is important in predicting the outcome after surgery. Klassen & Ahlskog found no clear coherence between symptom duration and shunt response [7]. This observation runs counter to other studies stating that a longer duration of symptoms prior to shunting yields a lower success rate [2, 29, 30]
Diagnostic and prognostic tests
There is no standardised way to diagnose iNPH, and various assessments have been applied. It is difficult to compare severity of symptoms and improvement after surgery as there is no consensus on the diagnostic protocol. Some common elements in today’s diagnostics include: one/two or more of the classic triad symptoms, normal intracranial pressure, and enlarged ventricles on CT/MRI, cereprospinal fluid (CSF) stasis/increased Rout or improvement of symptoms after CSF removal (tap test) [3-5, 10, 11,17, 21, 22, 26, 29, 31-34]. Some also included a lack of secondary causes in the diagnostic criteria [10, 17, 34].
Clinical tests
For evaluation of the clinical symptoms, various test batteries were applied in different series. The NPH Scale was applied for clinical assessment before shunting, and some authors used corresponding NPH grading systems for assessment of symptoms. These include evaluation of the severity of gait, cognitive and urinary problems. The minimum score is three and the maximum score is 15 [3, 4, 31, 35-37]. Other studies use similar grading systems for assessment [31, 37, 38]. Bech et al used scales from 1-5 (one is normal, five is worst condition) for gait disturbance and urinary incontinence [10, 21]. One study scored NPH and graded symptoms from 1-10, assessing gait, living condition and urinary symptoms [38]. The Mini Mental State Examination (MMSE) is widely used for evaluation of cognitive impairment [3, 10, 13, 16, 17, 19, 20, 21, 26, 30, 37]. Another tool used for assessment of cognitive deficits is the Global Deterioration Scale (GDS) [3, 4, 21].
More extensive scales are also used, but may be difficult to apply in everyday use [14, 15, 31, 35, 37, 38].
Computed tomographyEvans ratio is used to evaluate ventricular enlargement. An Evans index > 0.30 on CT confirms significant enlargement and is frequently used as a diagnostic criterion [3, 10, 16, 20, 23, 29, 31-33].
Intracranial pressure monitoringAn ICP-sensitive transducer is used to monitor prolonged ICP and amplitude changes. B-waves represent oscillations of ICP and are often recorded [3, 4, 10, 19, 21, 30, 32]. Eide & Sorteberg reported that when using ICP monitoring as a diagnostic tool for identification of iNPH patients, improvement after surgery can be expected in 90% of subjects [31].
Referencer
LITERATURE
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Art icles retrieved fro m reference lists
Adams RD, Fisher SM, Hakim S et al. Symptomatic occult hydrocephalus with
“normal” cerebrospinal-fluid pressure. A treatable syndrome. N Engl J Med
1965;273:117-26.
Bech RA, Waldemar G, Gjerris F et al. Shunting effects in patients with
idiopathic normal pressure hydrocephalus; correlation with cerebral and
leptomeningeal biopsy findings. Acta Neurochir (Wien) 1999; 141:633-9.
Meier U, Zeilinger FS, Schonherr B. Endoscopic ventriculostomy versus shunt
operation in normal pressure hydrocephalus: diagnostics and indication. Acta
Neurochir Suppl 2000;76:563-6.
Bech-Azeddine R, Waldemar G, Knudsen GM et al. Idiopathic normal-pressure
hydrocephalus: evaluation and findings in a multidisciplinary memory clinic.
Eur J Neurol 2001;8:601-11.
Kahlon B, Sjunnesson J, Rehncrona S. Long-term outcome in patients with
suspected normal pressure hydrocephalus. Neurosurgery 2007;60:327-
32;discussion 332.
Woodworth GF, McGirt MJ, Williams MA et al. Cerebrospinal fluid drainage
and dynamics in the diagnosis of normal pressure hydrocephalus.
Neurosurgery 2009;64:919- 25; discussion 925-6.
Katzen H, Ravdin LD, Assuras S. Postshunt cognitive and functional
improvement in idiopathic normal pressure hydrocephalus. Neurosurgery
2011;68:416-9.
Wikkelsø C, Hellström P, Klinge PM et al. The European iNPH multicentre study
on the predictive values of resistance to CSF outflow and the CSF Tap Test in
patients with idiopathic normal pressure hydrocephalus. J Neurol Neurosurg
Psychiatry 2013;84:562-8.
Saito M, Nishio Y, Kanno S et al. Cognitive profile of idiopathic normal pressure
hydrocephalus. Dement Geriatr Cogn Disord Extra 2011;1:202-11.
Liberati, A, Altman DG , Tetzlaff J et al. The PRISMA statement for reporting
systematic reviews and meta-analyses of studies that evaluate health care
interventions: explanations and elaboration. Ann Intern Med 2009;151:65-94.