Normal Pressure Hydrocephalus (NPH)

What is normal pressure hydrocephalus?

A distinctive form of adult hydrocephalus in which pressure is normal, but brain physiology is not.

Normal pressure hydrocephalus (NPH) is a condition in which cerebrospinal fluid (CSF) accumulates within the brain ventricles, leading to their progressive enlargement (ventriculomegaly), without persistently elevated CSF pressure on lumbar puncture.

When no clear antecedent cause is identified (such as subarachnoid hemorrhage, infection, or trauma), the condition is termed idiopathic NPH (iNPH). When a specific underlying cause is present, it is referred to as secondary NPH, which often demonstrates a more predictable response to treatment.

How common is it and at what age does it occur?

A frequently underdiagnosed disorder in older adults.

Idiopathic NPH occurs predominantly in individuals aged over 60–65 years. Epidemiologic studies report:

• an incidence of approximately 0.2–5.5 new cases per 100,000 persons per year,
• a prevalence of 0.2–2.9% in the population aged ≥ 65 years, depending on study criteria.

In everyday practice, NPH is often underdiagnosed, as many patients are labeled simply as having “dementia,” “normal aging,” or “orthopedic problems.” Early recognition of the triad (gait – cognition – urinary function) and appropriate imaging can significantly alter the disease trajectory.

What are the key symptoms?

The classic triad: gait disturbance, cognitive slowing, and urinary dysfunction.

Gait disturbance

Gait impairment is the most characteristic and often earliest symptom. Patients may develop:

• a sense of instability, particularly when turning or climbing stairs,
• a short-stepped, shuffling gait, as if the feet are “stuck to the floor” (“magnetic gait”),
• a wide-based stance, hesitation at gait initiation,
• difficulty turning, often using multiple small steps instead of a smooth pivot,
• frequent falls or fear of falling.

Cognitive impairment

Cognitive changes in NPH are primarily subcortical:

• slowed thinking and psychomotor retardation,
• difficulty with planning, organization, and execution of daily tasks,
• reduced attention and concentration,
• mild recent memory impairment—typically less severe than in Alzheimer’s disease.

Urinary dysfunction

Common manifestations include:

• urinary frequency and urgency,
• nocturia,
• in later stages, urinary incontinence, often without awareness of leakage.

Not all patients exhibit all three components simultaneously or with equal severity. However, the presence of gait disturbance combined with at least one of the other two strongly suggests NPH.

Why does it occur? What is known about the pathophysiology?

NPH is not due to CSF overproduction, but rather impaired brain compliance and altered CSF absorption.

The precise cause of iNPH remains unknown, but several mechanisms have been proposed:

• Reduced cerebrospinal compliance: the craniospinal system loses elasticity and cannot adequately buffer pulsatile CSF pressure changes.
• Atherosclerosis and vascular stiffening of major arteries, with loss of the Windkessel effect and increased shear stress on periventricular white matter.
• Structural changes in the subarachnoid cisterns and arachnoid granulations, including thickening, fibrosis, and inflammation, resulting in impaired CSF absorption.
• Regional hypoperfusion (e.g., around the corpus callosum), correlating with clinical symptoms.

Concomitant Alzheimer’s disease or vascular encephalopathy is common and may complicate the clinical picture and influence postoperative prognosis.

Which conditions mimic NPH? (Differential diagnosis)

Why “large ventricles” on CT alone are insufficient for diagnosis.

Many conditions may present with symptoms similar to NPH:

• Parkinson’s disease and other parkinsonian syndromes,
• cervical myelopathy due to spinal stenosis with spastic gait,
• peripheral neuropathies and vestibular disorders (dizziness, imbalance),
• degenerative and vascular dementias (Alzheimer’s, frontotemporal dementia, Lewy body disease),
• orthopedic disorders of the hips and knees,
• urologic conditions (benign prostatic hyperplasia, urinary tract infections, bladder prolapse).

Accurate differential diagnosis is essential: shunting should not be performed in patients with advanced dementia or other conditions when NPH is not the primary driver of symptoms.

How is the clinical evaluation performed?

A combination of history, neurological examination, gait testing, and cognitive assessment.

Clinical evaluation includes:

• detailed medical history (onset and progression of gait, cognition, urinary symptoms, falls, medications),
• comprehensive neurological examination, with emphasis on gait, reflexes, and balance,
• standardized gait testing (e.g., 10-meter walk test, Timed Up and Go),
• cognitive assessment using validated scales (MMSE, MoCA, executive function testing),
• evaluation of urinary function, potentially including urodynamic studies.

Screening for other reversible contributors is also performed: laboratory tests, thyroid function, vitamin B₁₂, folate, vitamin D, infection, and sleep disorders (e.g., sleep apnea).

What do imaging studies show?

Brain MRI/CT is essential, but requires expert interpretation.

On CT or MRI of the brain, we assess:

• Ventriculomegaly with an Evans index > 0.3 (ratio of maximal frontal horn width to inner skull diameter).
• Abnormal CSF distribution: disproportionate enlargement of the Sylvian fissures relative to the cortical sulci (DESH pattern).
• Reduced callosal angle (< 90°), mild compression of the corpus callosum.
• Absence of marked cortical atrophy or alternative pathology that fully explains symptoms (large infarct, tumor, etc.).

Additional studies may include:

• phase-contrast MRI to measure aqueductal CSF flow,
• cerebral perfusion studies (SPECT, PET) in selected cases.

No single imaging parameter alone guarantees a favorable response to shunting. Imaging must always be interpreted in conjunction with clinical findings and CSF drainage testing.

What are CSF tap testing and extended drainage?

Controlled “simulations” of permanent shunting to predict which patients will benefit from surgery.

To improve diagnostic accuracy and predict response to shunting, we employ:

High-volume lumbar puncture (tap test)

• removal of 30–50 mL of CSF via lumbar puncture,
• assessment of gait and balance before and in the hours following the procedure,
• improvement in walking speed, stride length, or stability suggests a high likelihood of benefit from shunting.

Extended lumbar drainage (External Lumbar Drain – ELD)

• placement of a fine catheter into the lumbar subarachnoid space,
• controlled CSF drainage over 2–3 days in hospital,
• serial gait and cognitive assessments during drainage.

Significant clinical improvement after tap testing or ELD strongly supports proceeding with shunt placement. Conversely, complete lack of improvement despite typical imaging reduces the likelihood of benefit and warrants careful deliberation.

When is surgery indicated and what types of shunts exist?

CSF diversion (shunting) is the standard treatment when benefits outweigh risks.

Surgical intervention is considered when:

• the clinical triad is consistent with NPH,
• imaging demonstrates characteristic ventriculomegaly without alternative explanation,
• tap testing and/or extended drainage demonstrate improvement,
• the patient’s overall condition permits anesthesia and surgery.

Types of shunts include:

• Ventriculoperitoneal (VP) shunt – the most common type, diverting CSF from the lateral ventricle to the peritoneal cavity.
• Ventriculoatrial (VA) or lumboperitoneal (LP) shunts – used in selected indications.
• Programmable valves, allowing noninvasive adjustment of flow resistance to minimize overdrainage and reduce the risk of subdural hematomas.

We typically begin with higher resistance settings and gradually adjust downward while closely monitoring gait, cognition, and imaging changes.

What outcomes can be expected?

Gait improves most consistently and to a greater degree than cognition or urinary function.

In well-selected patients:

• gait improvement is observed in ~75–90% within the first year,
• benefits in gait may persist for 2–4 years or longer,
• cognitive function improves in a smaller proportion (e.g., 30–60%), particularly when advanced dementia is absent,
• urinary symptoms improve in some patients, though not always completely.

In general, the earlier NPH is recognized and treated, the greater the likelihood of meaningful and sustained improvement. Long-standing, severe symptoms—especially when gait disturbance exceeds two years—are associated with a lower probability of full reversal.

What are the risks and complications of CSF diversion?

Surgery is generally safe, but informed consent and follow-up are essential.

Serious complications are relatively uncommon, but may include:

• Overdrainage of CSF with development of subdural hygromas or hematomas, potentially causing headache, confusion, or focal neurological deficits.
• Shunt-related infections (meningitis, peritonitis), which may necessitate removal or replacement of the system.
• Mechanical malfunction of the valve or tubing (obstruction, kinking, fracture), resulting in symptom recurrence.
• bleeding, seizures, anesthetic complications—less commonly.

Given patient age and comorbidities, general medical complications (respiratory infections, venous thrombosis) are not uncommon. Overall mortality in specialized centers is < 1%, and permanent severe morbidity < 5%.

Use of programmable valves and strict patient selection criteria significantly reduce the risk of major complications.