Normal Pressure Hydrocephalus

Quick Start

Definition	• Normal pressure hydrocephalus (often referred to as NPH) is a relatively rare disorder characterized by enlargement of the ventricles, a gait disorder, incontinence, and cognitive impairment. • It is thought to result from low-grade scarring or obstruction of the ventricular system or subarachnoid pathways.
Prevalence	• It is a relatively rare disorder, making up between 1% and 5% of patients referred to a memory clinic.
Genetic risk	• There are no known genetic or other risk factors.
Cognitive and behavioral symptoms	• The most common cognitive and behavioral presentation is that of a frontal subcortical disturbance including apathy, abulia, poor attention, and slowing of processing.
Diagnostic criteria	• Normal pressure hydrocephalus should be suspected when the triad of symptoms of cognitive impairment, gait disorder, and urinary incontinence are present in the setting of enlarged ventricles. • The frontal gait disturbance in normal pressure hydrocephalus, sometimes called a “magnetic gait” or a “marche à petits pas” (walk of little steps), is typically the most prominent symptom and is usually the earliest in onset. • Urinary incontinence generally occurs late in normal pressure hydrocephalus, and is associated with urinary urgency. • A CT or MRI scan showing enlargement of the ventricles and rounding of the ventricular contours, with or without periventricular abnormalities due to trans-ependymal flow of cerebrospinal fluid, is essential to making the diagnosis. • Serial lumbar punctures to withdraw 30–50 mL of CSF with pre– and post–lumbar puncture gait evaluations can help to determine both diagnosis and possible response to treatment. • Referral to a neurosurgeon for an evaluation including a lumbar drain or continuous ventricular pressure monitoring may be helpful.
Treatment	• A ventricular–peritoneal shunt provides the definitive treatment.
Top differential diagnoses	• Because many disorders can cause cognitive impairment, a gait disorder, and urinary incontinence, and virtually all dementias lead to dilatation of the ventricles, the differential diagnosis must be carefully considered.

A 76-year-old woman presented to the clinic with poor cognition over 6–12 months. Her family noted that she had poor memory and that she was easily distracted. After finding several bills unpaid, her daughter had taken over the management of her finances. She was also forgetting to take her pills, and her daughter needed to call to remind her twice each day to look in her pillbox and take her pills. Her daughter also remarked upon her walking; the patient used to walk for several miles each day but now she would tire walking more than a block or two. Review of systems was remarkable for urinary urge incontinence. Her physical examination was notable for a frontal or “magnetic” gait disorder with stiff legs and short steps, brisk reflexes, as well as grasp and palmomental reflexes bilaterally. Her ability to pay attention was so impaired that she was frequently distracted during our interview and examination. Tests of attention and executive function were impaired. Memory was impaired secondarily due to poor attention. Her head CT is shown in Figure 11-2 .

Prevalence, Prognosis, and Definition

Normal pressure hydrocephalus is a relatively rare disorder characterized by enlargement of the ventricles, a gait disorder, incontinence, and cognitive impairment. Although some studies have suggested that up to 5% of patients with dementia have normal pressure hydrocephalus, other studies have found the prevalence to be closer to 1%, which is consistent with our experience of patients referred to a memory disorders clinic (for a review see ). It may, however, be underdiagnosed in the general population; one study showed that 5.9% of individuals 80 years and older met criteria for normal pressure hydrocephalus ( ).

Criteria

Normal pressure hydrocephalus should be suspected when the so-called “triad” of symptoms (cognitive impairment, gait disorder, and urinary incontinence) is present in the setting of enlarged ventricles. However, it cannot be stated strongly enough that many disorders can cause cognitive impairment, a gait disorder, and urinary incontinence, and virtually all neurodegenerative diseases lead to ex vacuo dilatation of ventricles (enlarged ventricles due to loss of brain tissue), so the differential diagnosis of these symptoms and signs must be carefully considered. Frequently used criteria for diagnosing normal pressure hydrocephalus are shown in Box 11-1 .

Box 11-1

Criteria for Probable Normal Pressure Hydrocephalus

1.

History must include:
- a.
  
  Insidious onset
- b.
  
  Age 40 years or older
- c.
  
  Duration of symptoms greater than three months
- d.
  
  No evidence of an antecedent event known to cause hydrocephalus
- e.
  
  Progression of symptoms over time
- f.
  
  No other neurological, psychiatric, or medical condition that can explain the presenting signs and symptoms.
2.

Brain imaging:
- a.
  
  (CT or MRI) must show
  - 1)
    
    Ventricular enlargement not solely due to atrophy or congenital enlargement
  - 2)
    
    No visible obstruction of cerebrospinal fluid flow
  - 3)
    
    Callosal angle of 40 degrees or greater (rounding of the ventricular contours)
  - 4)
    
    Evidence of periventricular trans-ependymal flow of cerebrospinal fluid
  - 5)
    
    Aqueductal or fourth ventricular flow void on MRI.
- b.
  
  Supportive brain imaging (CT or MRI) findings include
  - 1)
    
    Prior brain imaging study showing smaller ventricular size
  - 2)
    
    Radionuclide cisternogram showing delayed clearance of radiotracer
  - 3)
    
    Cine MRI showing increased ventricular flow
  - 4)
    
    SPECT-acetazolamide challenge showing decreased perfusion not altered by acetazolamide.
3.

Clinical findings of gait/balance disturbance plus either cognitive impairment or urinary symptoms or both:
- a.
  
  Gait disturbance that includes at least two of the following (not entirely attributable to other conditions)
  - 1)
    
    Decreased step height
  - 2)
    
    Decreased step length
  - 3)
    
    Decreased cadence (speed of walking)
  - 4)
    
    Increased trunk sway during walking
  - 5)
    
    Widened standing base
  - 6)
    
    Toes turned outward on walking
  - 7)
    
    Spontaneous or provoked retropulsion
  - 8)
    
    En bloc turning (needing 3+ steps for turning 180 degrees)
  - 9)
    
    Impaired walking balance, tested by 2+ corrections needed for tandem gait of eight steps.
- b.
  
  Cognitive impairment that includes at least two of the following (not entirely attributable to other conditions)
  - 1)
    
    Psychomotor slowing (increased latency of response)
  - 2)
    
    Decreased fine motor speed
  - 3)
    
    Decreased fine motor accuracy
  - 4)
    
    Difficulty dividing or maintaining attention
  - 5)
    
    Impaired memory recall, especially for recent events
  - 6)
    
    Executive dysfunction, including impairment in multistep procedures, working memory, abstractions, similarities, and insight
  - 7)
    
    Behavioral or personality changes.
- c.
  
  Urinary incontinence not entirely attributable to other conditions consisting of either
  - 1)
    
    Episodic urinary incontinence
  - 2)
    
    Persistent urinary incontinence
  - 3)
    
    Urinary and fecal incontinence
    
    Or any two of the following
  - 4)
    
    Frequent perception of the need to void
  - 5)
    
    Urinary frequency
  - 6)
    
    Nocturia greater than two times per night.
4.

Physiological
- a.
  
  CSF opening pressure of 70–245 mmH ₂0 (5–18 mm Hg)