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Hydrocephalus, Normal Pressure
Dennis E. Hughes, DO, FACEP
image BASICS
DESCRIPTION
  • Normal pressure hydrocephalus (NPH) is a clinical triad of gait instability, incontinence, and dementia (mnemonic: wet, wobbly, wacky). Originally described by Hakim in 1957, it occurs rarely but is potentially treatable.
  • Two forms of the disorder: idiopathic and secondary (to trauma)
  • Absence of papilledema on clinical exam and normal CSF pressures at lumbar puncture
ALERT
Idiopathic NPH primarily affects persons >60 years; extremely rare before 40 years
EPIDEMIOLOGY
Incidence
  • No formal epidemiologic data exist regarding NPH because of the lack of consensus-derived diagnostic criteria. The natural history of untreated NPH has not been studied.
  • Idiopathic (iNPH) form primarily affects elderly, at least >40 years of age.
  • Secondary form can occur at any age.
  • Male = female
Prevalence
  • 3.3/100,000 age 50 to 59 years to 11.7/100,000 age 70 to 79 years for iNPH and increases to upwards of 5.9% in those ≥80 years
  • Estimated to be a contributing factor in 6% of all cases of dementia
ETIOLOGY AND PATHOPHYSIOLOGY
  • Idiopathic form is a communicating hydrocephalus, a disorder of decreased CSF absorption (not over-production). In iNPH, the leading theory suggests that poor venous compliance impairs the subarachnoid granulations' ability to maintain baseline removal of CSF. In secondary NPH, scarring is likely.
  • The result is a pressure gradient between the subarachnoid space and ventricular system.
  • CSF production decreases in the face of an increased pressure set-point (but still in excess of the amount of CSF absorbed).
  • Elevated pressure distends ventricles and compresses the brain parenchyma.
  • As a result of compression, ischemic changes occur in the parenchymal vasculature with subsequent tissue damage and loss.
  • Some believe that the idiopathic form is a result of persistently insufficient removal of CSF by immature subarachnoid granulations from childhood.
  • Secondary NPH may result from the following:
    • Head trauma (most common)
    • Subarachnoid hemorrhage
    • Resolved acute meningitis
    • Chronic meningitis (tuberculosis, syphilis)
    • Paget disease of the skull
RISK FACTORS
  • Idiopathic risk is unknown (case reports suggest a possible genetic link but unsubstantiated).
  • Secondary form is due to head trauma, subarachnoid hemorrhage, meningitis, or encephalitis.
image DIAGNOSIS
Detailed history and careful examination is the key to early diagnosis.
PHYSICAL EXAM
  • Decreased step height and length
  • Reduced speed of walking (cadence)
  • Widened standing base
  • Swaying of trunk during walking
  • Decreased fine motor speed and accuracy
  • Recall impaired for recent events
  • Impaired ability to do multistep tasks or interpret abstractions
DIFFERENTIAL DIAGNOSIS
  • Alzheimer disease (may be a comorbid condition in as many as 75%)
  • Parkinson disease
  • Chronic alcoholism
  • Intracranial infection
  • Multi-infarct dementia
  • Subdural hematoma
  • Carcinomatous meningitis
  • Collagen vascular disorders
  • Depression
  • Syphilis
  • B12 deficiency
  • Urologic disorders
  • Other hydrocephalus disorders
DIAGNOSTIC TESTS & INTERPRETATION
Initial Tests (lab, imaging)
  • Thyroid-stimulating hormone (TSH)
  • Syphilis serology
  • CBC
  • Serum B12, folate
  • Metabolic profile
  • Blood alcohol, analysis for drugs of abuse
  • Urinalysis
  • CSF analysis, including an opening pressure <245 mm H2O (a value greater than this rules out iNPH by definition)
  • Imaging is essential.
    • Either CT or MRI shows the ventriculomegaly (particularly lateral and 3rd ventricles) with preservation of the cerebral parenchyma (as opposed to ventricular enlargement seen in other forms of dementia where brain atrophy is present). A narrow subarachnoid space (“tight convexity”) was recently shown to correlate to probable or definite iNPH (3)[A].
    • MRI can allow detection of other features, such as signs of altered brain water content and callosal angles. However, these supportive findings are not independently diagnostic of NPH.
P.501

Diagnostic Procedures/Other
CSF removal aids in the definitive diagnosis as well as predicting response to surgical treatment.
  • High-volume (30 to 70 mL) CSF removal via spinal tap on 3 successive days or continuous spinal drainage (150 to 200 mL/day) for 3 days
  • Comparison of gait analysis before and after CSF removal (a ≥20% improvement indicates a positive test) especially when combined with coexisting executive function improvement (4)[B]
image TREATMENT
MEDICATION
  • No medication is significantly helpful.
  • Use of carbonic anhydrase inhibitors (acetazolamide) with repeat lumbar punctures has provided mild and transient relief but is only supported by anecdotal evidence.
  • Use of levodopa to rule out Parkinson disease may be helpful (NPH will display little, if any, significant improvement to dopamine agonist).
ISSUES FOR REFERRAL
  • Neurology or neurosurgical consultation is helpful in suspected cases when other reversible medical conditions are ruled out.
  • Recent cohort studies have demonstrated clinical improvement after surgical shunts. Perimeters of urinary continence, gait stability, and cognitive scores all improved at 1-year post shunt.
ADDITIONAL THERAPIES
Gait training and use of ambulation assist devices, as indicated, but limited efficacy
SURGERY/OTHER PROCEDURES
  • Current therapy is limited to placement of ventriculoperitoneal or ventriculoatrial shunt from a lateral ventricle tunneled SC and drained into the peritoneal cavity (or right atrium). There is no compelling evidence (no randomized controlled trial [RCT]) that this therapy is effective.
  • Patients whose symptoms have been present for a shorter period (<2 years) have a greater chance of improvement with shunting. Also, patients with a known cause of NPH tend to respond more favorably. However, improvement has been seen in patients with symptoms present for a long time (5)[B].
INPATIENT CONSIDERATIONS
Admission Criteria/Initial Stabilization
Usually only for planned surgical treatment
image ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
  • Assessment and modification of environment for fall risks
  • Evaluation for ability to operate a motor vehicle safely (if driving)
Patient Monitoring
  • Repeat neuropsychological testing to evaluate the status of the dementia after treatment.
  • Improvement in the incontinence and walking speed can also be objectively measured.
PATIENT EDUCATION
Information at: http://www.ninds.nih.gov/disorders/normal_pressure_hydrocephalus/normal_pressure_hydrocephalus.htm
PROGNOSIS
Natural history is progressive deterioration. Patient's axial skeletal stability worsens with inability to walk, stand, sit, or turn over in bed.
REFERENCES
1. Oliveira MF, Oliveira JR, Rotta JM, et al. Psychiatric symptoms are present in most of the patients with idiopathic normal pressure hydrocephalus. Arq Neuropsiquiatr. 2014;72(6):435-438.
2. Williams MA, Relkin NR. Diagnosis and management of idiopathic normal-pressure hydrocephalus. Neuro Clin Pract. 2013;3(5):375-385.
3. Hashimoto M, Ishikawa M, Mori E, et al. Diagnosis of idiopathic normal pressure hydrocephalus is supported by MRI-based scheme: a prospective cohort study. Cerebrospinal Fluid Res. 2010;7:18.
4. Allali G, Laidet M, Beauchet O, et al. Dual-task related gait changes after CSF tapping: a new way to identify idiopathic normal pressure hydrocephalus. J Neuroeng Rehabil. 2013;10:117.
5. Razay G, Vreugdenhil A, Liddell J. A prospective study of ventriculo-peritoneal shunting for idiopathic normal pressure hydrocephalus. J Clin Neurosci. 2009;16(9):1180-1183.
Additional Reading
&NA;
  • Andrén K, Wikkelsø C, Tisell M, et al. Natural course of idiopathic normal pressure hydrocephalus. J Neurol Neurosurg Psychiatry. 2014;85(7):806-810.
  • Ghosh S, Lippa C. Diagnosis and prognosis in idiopathic normal pressure hydrocephalus. Am J Alzheimers Dis Other Demen. 2014;29(7):583-589.
  • Jaraj D, Rabiei K, Marlow T, et al. Prevalence of idiopathic normal-pressure hydrocephalus. Neurology. 2014;82(16):1449-1454.
See Also
&NA;
Algorithm: Ataxia
Codes
&NA;
ICD10
  • G91.2 (Idiopathic) normal pressure hydrocephalus
  • G91.0 Communicating hydrocephalus
  • G91.3 Post-traumatic hydrocephalus, unspecified
Clinical Pearls
&NA;
  • Consider in unexplained dementia or behavioral change
  • Poor prognosis without therapy