9 Normal pressure hydrocephalus grading scales
Adult Hydrocephalus, ed. Daniele Rigamonti. Published by Cambridge University Press. © Cambridge University Press 2014.
Introduction
Hakim and Adams [1] first described a surgically treatable syndrome in patients with symptoms of gait, cognition and urination, ventriculomegaly, and normal cerebrospinal fluid (CSF) pressure. The syndrome is now well known as normal pressure hydrocephalus (NPH). NPH can etiologically be divided into two types: idiopathic and secondary. Secondary NPH (sNPH) can develop within several weeks or months after a subarachnoid hemorrhage or meningitis. In contrast, idiopathic normal pressure hydrocephalus (iNPH) has no identifiable causes. The recent and rapid increase of the elderly population in developed nations has heightened the social importance of precise diagnosis and appropriate treatment for iNPH. An accurate assessment of symptoms and findings on neuroimaging is therefore important in selecting candidates for CSF shunt surgery. In this chapter, we critically review various assessment batteries that have been used in iNPH to date.
Scales
There are many NPH assessing scales, most of which aim to assess (1) level of general activity, (2) severity of respective NPH symptoms, (3) response to interventions such as cerebrospinal fluid (CSF) drainage tests or shunt surgery, and (4) short- and long-term outcome. More recently, the caregiver burden is also being assessed. The requirement of any grading scale should be to clearly define each symptom and be highly reproducible by different observers. They should be able to detect the degree of change in symptoms following interventions such as CSF drainage or CSF shunt surgery. Most assessment scales are qualitative and some are quantitative. The criticism leveled against qualitative assessments is that, although clinically useful, each grade of the scale might not span a similar interval, that the scale itself might exhibit inter-observer difference, and that data are not normalized. In contrast, while quantitative assessments are objective, they may reflect a limited part of NPH symptomatology. It is clear that comparative studies of various grading scales are necessary.
General activity
The well-known NPH scale created by Stein and Langfitt [2] (Table 9.1) assesses a patient’s daily activity. This scale is closely related to the modified Rankin Scale [3] (Table 9.2), which is a widely used scale for measuring the degree of disability or dependence in the daily activities of patients with various disorders including NPH. Both scales are useful for assessing the patient’s general level of activity; they are not quantitative and they display some indistinctness between the four to seven grades that characterize them.
Table 9.1 Stein–Langfitt classification (used with permission from reference 2)
Table 9.2 Modified Rankin Scale (used with permission from reference 3)
NPH symptomatology assessment
Qualitative assessment
Gait disturbance, dementia, and urinary incontinence are the cardinal symptoms of NPH. Most NPH grading scales classify the severity of the NPH triad. Black’s classification [4] (Table 9.3) has been long used for assessing the NPH triad: each domain of the triad is graded on a 4-point scale. Krauss et al. [5] (Table 9.4) also classified each symptom into four grades. However, because the parameters of each grade are rather ambiguous, this causes inter-observer difference. Furthermore, mild changes following interventions such as CSF drainage or shunting operation are poorly reflected. To overcome these drawbacks, the grading scales increased to five or more grades. Although these grading systems are basically composed of ordinal data, they are often regarded as continuous data and make a total [6] (Table 9.5). This makes it possible to assess relatively mild changes and to compare data before and after the interventions. Kubo et al. [7] confirmed that their five grades in each domain and their total showed high correlation with other qualitative or quantitative measures (Table 9.6). Kiefer et al. [8] added the assessment of headache and dizziness to the NPH triad and graded seven scales in degree. This could be useful for assessment of mild changes in symptoms caused by shunt malfunction or overdrainage during the follow-up period.
Table 9.3 Black’s classification (used with permission from reference 4)
Quantitative or semiquantitative assessment
The timed up and go test (TUG) [9] is often used for quantitative assessment of gait in senile patients who are at risk of falls. The TUG measures, in seconds, the time a person takes to stand up from a standard armchair, walk 3 meters, turn, walk back to the chair, and sit down again. A time less than 10 seconds is regarded as normal. A score of more than or equal to 14 seconds has been shown to indicate a high risk of falls. Steps are also measured. TUG requires not only the ability to walk but also the understanding of orders. The ten-meter walk test is commonly used for assessment of gait speed. For older adults, the mean comfortable gait speed at 60 years is 135.9 cm/s for men and 129.6 cm/s for women [10]. These measurements are useful to compare the time or steps before and after the interventions such as the tap test or shunt surgery. Changes of gait can be assessed with video recording. However, there is no consensus for the cut-off level for defining improvement after CSF drainage or shunt surgery.
Dementia is a major symptom of NPH. Various kinds of neuropsychological tests have been used for assessment. For example, Kubo et al. [7] used the mini-mental state examination, frontal assessment battery and Trail Making Test A and B. Thomas et al. [11] used the Wechsler Memory scale, Rey–Osterrieth Complex Figure, Rey Auditory Verbal Learning Test, Line-Tracing test, Stroop Color and Word Test, and some others. Hellström et al. [12] used the Grooved Pegboard, the Rey Auditory Verbal Learning Test, and the Swedish Stroop test. Comparative study of the specificity and sensitivity of these neuropsychological tests is necessary to determine the most reliable test for prediction of shunt surgery.
Urinary incontinence is also a major symptom of NPH. Apart from various NPH grading scales, the international consultation on incontinence questionnaire-short form (ICIQ-SF) is also used [13].
Combination of qualitative and quantitative assessment
Hellström et al. [12] proposed a new NPH scale based on the idea that an iNPH scale should be discriminative, that is, it should distinguish well between patients with different levels of symptom severity, but also between iNPH patients and healthy individuals.
The scale consists of the four domains of gait, neuropsychology, balance, and continence (Table 9.7). The former two domains are continuous data and the latter two domains are ordinal data. All scores are calibrated and norm-based using data from an age-matched healthy population. Their NPH scale is well designed with a good statistical basis. However, it is complicated, and its use in clinical practice may be difficult.
Table 9.7 Hellström’s classification (used with permission from reference 12)Gait
The domain score is the mean value of available converted score.
Comorbidity
Comorbidity is one of major issues in the management of patients with iNPH.
Kiefer et al. [14] proposed a comorbidity index (Table 9.8). Comorbidity is divided into vascular risk factors, peripheral vascular occlusions, cerebrovascular disease, heart, and others, and each symptom or disease has to be assigned according to the indicated parameter-values (1–3 points). The sum represents the individual comorbidity index.
Table 9.8 Kiefer’s comorbidity index (used with permission from reference 14)
ICA, internal carotid artery; TIA, transient ischemic attack; PRIND, prolonged reversible ischemic neurologic deficit.
Further study is necessary to define the clinical significance of each parameter relevant to the clinical outcome.
Caregiver burden scale
In addition to assessing the patient’s symptoms or general activity, the change in caregiver burden is a useful measure to assess the patient’s ability to cope with daily life. Kazui et al. [15] assessed the change in caregiver burden after shunt surgery. They used the Zarit caregiver burden scale [16] and noted significant improvement in the total score and the personal strain factor one year after surgery, but not in the role strain. The improvement of cognitive impairment was the major factor in reducing caregiver burden.
Balance
Continence
Comparison between scales
There are many assessing scales for NPH: the degree of difference between them is not known. This unknown factor might explain, at least in part, the difference between the results of large cooperative studies. For example, the Japanese cooperative study for NPH [17] reported 80% improvement at one year after shunt operation assessed by the grading scale reported by Kubo et al. [7]. In contrast, the European cooperative study [18] reported 92% improvement using the grading scale reported by Hellström et al. [12]. While there appears to be a difference in the improvement rate between the two studies, assessment on the modified Rankin Scale showed 69% improvement in both studies. This discrepancy seems to suggest that the grading scale with more parameters can demonstrate higher improvement rates than that with fewer parameters. To overcome this problem, we need to use the same assessment measures for NPH.
Conclusion
Many grading scales for assessing general activity and symptoms of NPH are readily available from the literature. However, most of them are not validated and normalized. It clearly behooves the medical community to develop standardized measures for NPH assessment without further delay.
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22 – Low-pressure syndromes and cerebrospinal fluid leaks
24 – Management of hydrocephalus with associated cerebrospinal fluid pathologies
19 – Endoscopic third ventriculostomy
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