Normal Pressure Hydrocephalus

General Information

Normal pressure hydrocephalus (NPH) is a syndrome characterized by gait impairment, cognitive decline, and urinary incontinence, and is associated with ventriculomegaly in the absence of elevated cerebrospinal fluid (CSF) pressure.

  • Idiopathic NPH: without known precipitant
  • Secondary NPH: occurs due to other disease processes, including subarachnoid hemorrhage, traumatic brain injury, cerebral infarction and meningitis

Clinical Presentation

  • Triad of gait disturbance, dementia and urinary incontinence
    • The entire triad need not be present
    • Symptoms typically develop insidiously
    • Generally occurs between the sixth and eighth decades of life
  • Gait disturbances: typically the first signs of INPH, and have been variously described as apraxic, bradykinetic, glue-footed, magnetic, parkinsonian and shuffling; often present with a history of falls; no significant motor weakness.
  • Cognitive deficits: typically of the subcortical type, characterized by inattention, psychomotor retardation and difficulty with executive function.
  • Urinary Incontinence: in the early stages of INPH, urinary frequency and urgency are present. With disease progression, urinary and even fecal incontinence can be observed. Urodynamic testing demonstrates bladder hyperactivity

Differential Diagnosis

  • Neurodegenerative diseases, vascular etiologies and urological disorders: peripheral neuropathy, cervical or lumbar stenosis, arthritis, vestibular diseases and Parkinson’s disease.
  • Dementia: Alzheimer’s dementia, diffuse Lewy body disease and vascular dementia – the absence of apraxia, agnosia and aphasia can help differentiate INPH from cortical dementias.

Diagnosis: based on history, physical exam, neuroimaging, and exclusion of other causes.

  • Imaging:
    • CT or MRI to assess ventricular size
      • Ventricular enlargement is necessary to establish the diagnosis of INPH for patients with appropriate symptoms
      • A frontal horn ratio (Evans’ index), defined as the maximal frontal horn ventricular width divided by the transverse inner diameter of the skull, signifies ventriculomegaly if it is 0.3 or greater.
    • Other radiographic findings associated with INPH include the following:
      • Periventricular hyperintensities, which are often associated with subcortical microvascular ischemia
      • Increased CSF flow velocity in the aqueduct
      • Thinning and elevation of the corpus callosum on sagittal images
      • No visible evidence of obstruction to CSF flow.
    • Lumbar Puncture: large-volume LP, involves the withdrawal of 40–50 ml of CSF
      • Symptomatic improvement after CSF removal increases the likelihood of a favorable response to shunt placement (positive predictive value 73–100%)
      • Low sensitivity (26–61%), however, and a negative test cannot be used to exclude a diagnosis of INPH

Treatment:

Accomplished through surgical diversion of CSF. This is accomplished by implanting a shunt to drain CSF from either the intracranial ventricular system or the lumbar subarachnoid space to a distal site, such as the peritoneal or pleural cavity or the venous system, where the CSF can be reabsorbed. The most common shunts utilized today are ventriculoperitoneal (VP) and ventriculoatrial (VA) shunts.

Nature Clinical Practice Neurology (2005) 2, 375-381; doi:10.1038/ncpneuro0237

Image courtesy of Radiopaedia.org