#034 Normal Pressure Hydrocephalus
Authors: Matthew Koeberl MD, Joseph Budovec MD, Steven Denson MD
Context: Diagnosis of Normal pressure hydrocephalus
Action: Appropriate clinical response when brain imaging tests raises the suspicion of NPH
Background: Patients presenting with gait disturbance, cognitive decline, or urinary incontinence present a common clinical dilemma for clinicians (1). This constellation of symptoms, while suggestive of NPH, can commonly occur in other neurodegenerative conditions or nonspecifically in advanced age (1). While some of the cases of NPH are due to prior meningitis, encephalitis, subarachnoid hemorrhage, or trauma; many causes remain idiopathic (2). Some people think that memory loss, difficulty finding words, walking problems, or urination problems are normal parts of aging. In many cases, however, these are symptoms of treatable conditions. Any of these problems, or changes in mood or behavior, warrants a visit to your health care provider. Patients with NPH may have typical imaging features of this disease process. However, a clinician may order brain imaging for other symptoms and the interpreting radiologist may raise the suspicion for NPH. This can lead to confusion for the clinician and patient anxiety.
Incidence/Prevalence: Normal pressure hydrocephalus is uncommon, accounting for only 6% of all cases of dementia worldwide (3,4). In Norway, Brean and Eide demonstrated an incidence of 5.5 per 100,000 and a prevalence of 21.9 per 100,000 for suspected idiopathic normal pressure hydrocephalus (5). This prevalence ranged from 3.3 per 100,000 for people 50 to 59 years of age, to 49.3 per 100,000 for people 60-69 years of age, to 181.7 per 100,000 for people 70-79 years of age (5). A study of nursing home patients found that at least 21.2% of nursing home patients have gait impairment, 9.4% of which also have dementia, and 14.7% also have incontinence (6). The overall likelihood of identifying a treatable NPH in these patients is low (7), but the importance of recognizing these symptoms is nonetheless important.
Imaging: Both computed tomography (CT) and magnetic resonance (MR) may demonstrate findings suggestive of the NPH. The most commonly described finding suggesting NPH is enlargement of the ventricles out of proportion to sulcal atrophy, commonly referred to as ventriculosulcal disproportion and/or ventriculomegaly. As with many imaging tests, the suggestion of NPH based on imaging is not diagnostic of the disease and clinical correlation with history, symptoms, and physical exam is warranted. If there is uncertainty, a neurological consult may be warranted.
While findings of ventriculomegaly are the most commonly described features suggestive of NPH on imaging, other findings on MR can also lead to a suggestion of NPH. Additional MR findings include:
Abnormal CSF flow, specifically increased flow through the cerebral aqueduct.
Abnormal brain signal about the ventricles, suggestive of transependymal CSF flow.
50-60% of patients with NPH will have periventricular and deep white matter lesions.
MR Spectroscopy (MRS) can demonstrate lactate peaks in the lateral ventricles in NPH patients, but not in those with other types of dementia.
Diffusion Tenor Imaging (DTI) is an MR technique which can be used to evaluate white matter pathology, and some studies have demonstrated that white matter changes can help distinguish between NPH and various dementias (8).
Nuclear medicine studies have also been used to evaluate NPH. Indium-111 DTPA (diethylene triamine penta-acetic acid) can be instilled in the CSF via a lumbar puncture. Normally, the tracer is resorbed over the convexities in 2-24hrs. In NPH, reflux of the tracer into the ventricles is seen with lack of tracer accumulation over the convexities 24-48 hours after instillation. Patients with this appearance may respond better to shunting than patients with a normal or equivocal In-111 DTPA study (9). Other nuclear medicine studies such as 18F-FDG PET also may be used to evaluate for NPH, but are reserved for a more advanced clinical evaluation.
Underlying Science: NPH is a communicating hydrocephalus which often results from impaired reabsorption of CSF into the venous sinuses (2). NPH is a challenging diagnosis, as there are numerous overlapping conditions, including advanced age, which can present with similar complaints. While current imaging techniques can be used to suggest this disease entity, clinical correlation with patient symptoms is crucial to making the diagnosis of NPH. In cases where there is a discordance of imaging findings and clinical findings, neurological consultation should be considered.
Objectives: Review the role of imaging in the diagnosis of normal pressure hydrocephalus (NPH)
ACGME Competencies: Patient care, Practice-based learning and improvement, Medical Knowledge
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Kim MJ, Seo SW, Lee KM, et al. differential diagnosis of idiopathic normal pressure hydrocephalus from other dementias using diffusion tensor imaging. Am J Neuroradiol 2011;32:1496-1503.
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Author Affiliation: Medical College of Wisconsin, Milwaukee, Wisconsin.
Geriatric Fast Facts are edited by the faculty of the Geriatric Education Teams (GETS) program funded by the Reynolds Foundation, Kathryn Denson, MD, Steven Denson, MD, & Edmund Duthie, MD from the Division of Geriatrics, Medical College of Wisconsin, and are published by the Geriatric Fast Facts Website at the Medical College of Wisconsin. For more information write Kathryn Denson, MD. More information, as well as the complete set of Fast Facts, available at www.mcw.edu/Geriatric-Fast-Facts.htm
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