Diagnosis and Treatment of Idiopathic Normal Pressure Hydrocephalus

Abstract

Purpose of review: This article provides neurologists with a pragmatic approach to the diagnosis and treatment of idiopathic normal pressure hydrocephalus (iNPH), including an overview of: (1) key symptoms and examination and radiologic findings; (2) use of appropriate tests to determine the patient's likelihood of shunt responsiveness; (3) appropriate referral to tertiary centers with expertise in complex iNPH; and (4) the contribution of neurologists to the care of patients with iNPH following shunt surgery.

Recent findings: The prevalence of iNPH is higher than previously estimated; however, only a fraction of persons with the disorder receive shunt surgery. iNPH should be considered as a diagnosis for patients with unexplained symmetric gait disturbance, a frontal-subcortical pattern of cognitive impairment, and urinary urge incontinence, whose MRI scans show enlarged ventricles and whose comorbidities are not sufficient to explain their symptoms. Physiologically based tests, such as the tap test (large-volume lumbar puncture) or temporary spinal catheter insertion for external lumbar drainage with gait testing before and after CSF removal, or CSF infusion testing for measurement of CSF outflow resistance, can reliably identify patients who are likely to respond to shunt surgery. Properly selected patients have an 80% to 90% chance of responding to shunt surgery, and all symptoms can improve following shunt surgery. Longitudinal care involves investigating the differential diagnosis of any symptoms that either fail to respond to shunt surgery or that worsen after initial improvement from shunt surgery.

Summary: Neurologists play an important role in the identification of patients who should be evaluated for possible iNPH. With contemporary diagnostic tests and treatment with programmable shunts, the benefit-to-risk ratio of shunt surgery is highly favorable. For more complex patients, tertiary centers with expertise in complex iNPH are available throughout the world.

Figure 10-1

This schematic drawing illustrates various models of the pathophysiology of idiopathic normal pressure hydrocephalus (iNPH). Any model must explain how and why the ventricles enlarge, how neuronal and glial dysfunction occurs to produce the clinical features, and why symptoms improve with shunt surgery (ie, reversible neuronal and glial dysfunction). Proposed disturbances in the CSF dynamic system that contribute to ventricular enlargement and dysfunction of the brain parenchyma include impaired CSF outflow resistance and increased intracranial pressure pulsatility. The gait and cognitive disturbances of iNPH are thought to be of periventricular/subcortical/frontal origin. The arterial supply of this area is mainly via periventricular end arteries, sensitive to a subcritical ischemia that causes dysfunction, but not infarction in an anatomic distribution, that affects the axons related to symptoms (eg, those to the leg, as represented in the homunculus). The altered CSF dynamics and reduced subcortical blood flow and metabolism may give rise to periventricular hyperintensities seen on MRI in iNPH. CSF = cerebrospinal fluid; ICP = intracranial pressure.

Figure 10-2

MRI of a 73-year-old woman with impairment of gait and balance, bladder control, and cognition for 3 years. A, Axial T2 MRI consistent with the Japanese “high and tight” criteria for the convexity. The interhemispheric fissure is effaced. B, Axial T1 MRI shows a widened third ventricle with a span of 1.0 cm. C, Sagittal T1 MRI shows bowing of the corpus callosum and a pulsation artifact (flow void) in the sylvian aqueduct D, Axial fluid-attenuated inversion recovery (FLAIR) MRI shows measurement of the Evans ratio. The diameter of the frontal horns is 4.4 cm, the widest brain diameter is 13.7 cm, and the Evans ratio is 0.32. Reprinted with permission from Williams MA, Relkin NR, Neurol Clin Pract. cp.neurology.org/content/3/5/375.full. © 2013 American Academy of Neurology.

Figure 10-3

Lateral skull x-ray showing the three components of a shunt: the proximal catheter (yellow arrow), the valve (red arrow), and the distal catheter (blue arrow).

Figure 10-4

Serial axial CT scans without contrast over a 6-week period showing the evolution of enlarging bilateral subdural fluid collections (A, from January 3; B, from January 7; C, from January 12) and resolution of the subdural fluid collections after the adjustable shunt was placed at the highest setting (D, from February 16).

Figure 10-5

Flowchart illustrating the diagnostic workup at the Department of Clinical Neuroscience, Umeå University, Sweden, including diagnosis at discharge. iNPH = idiopathic normal pressure hydrocephalus; NPH = normal pressure hydrocephalus.

Figure 10-6

Insertion of a 16-gauge spinal catheter via a 14-gauge Touhy needle for external lumbar CSF drainage.

Figure 10-7

Imaging from the patient in Case 10-1. The Evans ratio is 0.40. The widening of the sulci in the frontal lobes (A, B) suggests atrophy; however, the pattern also raises the possibility of disproportionately enlarged subarachnoid space hydrocephalus (DESH), particularly the widening of the sulci higher over the convexities (B, arrows).