Guidelines for Diagnosis and Management of Idiopathic Normal Pressure Hydrocephalus

In 1965, Hakim and Adams described 3 patients with normal pressure hydrocephalus who responded to treatment with a ventriculoatrial shunt. Afterward the adoption of shunt treatment without clear diagnostic criteria and surgical techniques resulted in poor outcomes with significant complications. The clinical practice guidelines for the diagnosis and treatment of idiopathic normal pressure hydrocephalus were first published by the Japanese Neurosurgical Society in 2004 and the international guidelines were published in 2005. Both guidelines led to diagnosis and treatment algorithms and significantly improved outcomes, along with decreased surgical risk. These guidelines should be reevaluated and updated on a regular basis.

Key points

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Idiopathic normal pressure hydrocephalus (iNPH) was identified in 1965, but poor diagnostic and treatment criteria initially led to poor patient outcomes.
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The development of clinical practice guidelines requires a rigorous and transparent process.
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The first guidelines for the diagnosis and treatment of iNPH were provided by the Japanese Hydrocephalus Society in 2004, followed by the International Guidelines in 2005.
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These guidelines provided a diagnosis and treatment algorithms that were adopted and extensively used resulting in a significant imptovement in patient outcomes.
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Patients with iNPH almost always have a gait abnormality.

Abbreviations

AHCRN	adult hydrocephalus clinical research network
CSF	cerebrospinal fluid
iNPH	idiopathic normal pressure hydrocephalus
sNPH	secondary NPH

Introduction

In 1965, Hakim and Adams described 3 patients with normal pressure hydrocephalus who responded to treatment with a ventriculoatrial shunt. These patients presented with ventriculomegaly and a triad of symptoms that included gait and balance difficulties, cognitive decline and urinary urgency, frequency, and incontinence. Hakim coined the term normal pressure hydrocephalus (NPH) to describe this treatable syndrome . The interest this generated with the hope to treat gait/balance difficulties and dementia with a cerebrospinal fluid (CSF) shunt system was significant. However, the lack of clear diagnostic criteria or reliable diagnostic methodology, coupled with the use of both unsophisticated shunt systems and unrefined surgical techniques meant that patient selection was frequently inappropriate, surgical complications were high, and poor outcomes predominated. This was highlighted in a 2001 systematic review reported by Hebb and Cusuimano :

Overall, 59% (range, 24%–100%) of patients improved after shunting, and 29% (range, 10%–100%) of patients experienced prolonged improvement. Complications occurred in 38% (range, 5%–100%) of patients, additional surgery was required in 22% (range, 0%–47%) of patients, and there was a 6% (range, 0%–35%) combined rate of permanent neurological deficit and death.

What transpired afterward was a polarization within the medical community with those who did not believe in NPH ^, and, fortunately, those who undertook to better understand the disorder and ultimately improve diagnosis and treatment. These latter groups eventually reached a point where clinical practice guidelines could be developed and later refined to guide the neurology and neurosurgical communities to improve standards of care. The following 2 statements eloquently describe the value of clinical practice guidelines:

Clinical practice guidelines are systematically developed statements to assist practitioner and patient decisions about appropriate health care for specific clinical circumstances.

Clinical practice guidelines are systematically developed statements that intend to assist clinicians and patients in making decisions about appropriate health care in specific circumstances. Guidelines aim to improve the quality of patient care by encouraging interventions of proven benefit and discouraging the use of ineffective or potentially harmful interventions, to reduce unnecessary variation in practice, to lessen disparities, to empower patients, and to influence public policy.

The rigor associated with creating clinical practice guidelines has evolved since the concept was first introduced. Graham, and colleagues, in 2011, described the basic features associated with reliable clinical practice guidelines. These have been updated here to reflect current expectations and requirements.

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They should be based on a systematic review of the literature. The standards for a systematic review and meta-analysis have evolved since the first iNPH guidelines in 2004 and 2005. The current requirements are thoroughly illustrated by examining the Cochrane Systematic Review process ( https://www.cochransincelibrary.com/cdsr/about-cdsr#:∼:text=A%20Cochrane%20review%20is%20a,answer%20a%20specific%20research%20question .)
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Systematic reviews should follow the established guidelines appropriate for the particular type of systematic review that is planned. The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyzes) guidelines are an example.
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Systematic reviews should be registered before they begin. The most common international prospective registry of systematic reviews used is PROSPERO ( https://www.crd.york.ac.uk/prospero/ ). ^,Other less commonly used alternative registries that are specific to systematic reviews include INPLASY and Research Registry.
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If the systematic review data warrants a meta-analysis, a biostatistician familiar with the intricacies of this type of statistical analysis and data synthesis should be consulted. Not all systematic reviews are appropriate for meta-analysis ( https://training.cochrane.org/handbook/current/chapter-10 ).
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The members of the clinical guidelines group should be experts in their fields representing a multidisciplinary and diverse background for all major affected groups. All members should declare any conflicts of interest.
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The process should include the determination as to whether subgroups of affected patients can be identified as this may influence the specificity of individual practice guidelines.
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The process should incorporate patient values, preferences, and quality of life outcomes if available.
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The systematic review should be undertaken with explicit and transparent processes to minimize biases.
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The systematic review should include use of a risk of reporting bias tool to evaluate the credibility (quality and strength) of the evidence reported in articles. ^,
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The strength of a recommendation developed from the systematic review should be included for the clinical practice guidelines. The strength of a recommendation should be based upon the quality of the evidence and an understanding of the benefit-risk balance. It should also incorporate patient values and preferences and address the possibility of resource limitations.
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Recommendations for which there is no strong evidence can potentially be developed using a structured and transparent consensus process. ^,
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The recommendations should include a clear explanation of the rationale for diagnostic and treatment choices as they relate to patient outcomes and health care system resources.
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Ultimately, these recommendations should assist the care givers and patients in selecting diagnostic and treatment strategies with information regarding the risks and benefits, including an understanding of the natural history of the disease without treatment.
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Clinical practice guidelines should be revaluated both as part of a regular scheduled process and also on an ad hoc basis when new evidence may significantly change recommendations.

In addition to allowing the standardization and improvement of patient care, the development of clinical practice guidelines often leads to an increase in research, increases in both education and awareness, and ultimately may enhance cost-effectiveness by fostering more efficient resource utilization.

Adult hydrocephalus

Adults with hydrocephalus represent a diverse spectrum of varying pathophysiology, clinical and radiological findings and treatment requirements and response. The International guidelines from 2005 dealt with iNPH but also included secondary NPH (sNPH) as part of the population and defined NPH as occurring in those ≥40 years of age. While these patients may share some features of the NPH phenotype (Hakim’s triad) they typically have major differences in age, underlying etiology, treatment options, treatment response, and prognosis.

The adult hydrocephalus clinical research network (AHCRN) proposed a pragmatic clinical classification for adult patients with hydrocephalus that includes: (1) transitional, (2) unrecognized congenital, (3) acquired, and (4) iNPH ( Table 1 ). Patients who present with a clinical suspicion of idiopathic hydrocephalus are classified as suspected iNPH until diagnostic tests have determined if they meet the criteria for a diagnosis of iNPH. This is discussed in greater detail by Williams in this issue.

Table 1

Pragmatic clinical classification of adult hydrocephalus

Type of Hydrocephalus	Description
Transition	Patients treated for hydrocephalus of any etiology before the age of 18 y
Acquired	Patients with hydrocephalus secondary to known risk factors (eg, subarachnoid hemorrhage, traumatic brain injury, brain tumor), whether treated or untreated
Unrecognized congenital	Patients with either or both imaging features and large head circumference consistent with congenital hydrocephalus, but not recognized or treated before age 18 y
Idiopathic normal pressure	Patients age ≥60 y referred for evaluation of iNPH who had not previously received surgical treatment are classified as suspected iNPH until diagnostic tests determine if they meet the criteria for iNPH