What are the clinical features, diagnosis, and treatment options for normal pressure hydrocephalus (NPH) in individuals over 60 years old?

Normal Pressure Hydrocephalus: Clinical Features, Diagnosis, and Treatment

Clinical Features

NPH presents with a characteristic clinical triad of gait disturbance, urinary incontinence, and cognitive impairment, with gait abnormalities appearing first in approximately 70% of patients and serving as the cardinal presenting symptom. 1

Symptom Progression and Characteristics

• Gait disturbance manifests as a hypokinetic pattern where the feet appear "glued to the floor" or "magnetic," occurring in approximately 70% of NPH patients and typically presenting as the initial symptom 2
• Cognitive impairment develops later in the disease course, presenting with frontal lobe dysfunction including psychomotor slowing, deficits in attention, working memory, verbal fluency, and executive function 1
• Urinary incontinence represents the third component of the triad, developing as the disease progresses 3
• Patients typically present late due to the slow and gradual nature of symptom onset 3

Epidemiology and Clinical Context

• NPH affects approximately 3.7% of patients over 65 years of age 1
• This represents one of the few potentially reversible causes of dementia 1
• Critical caveat: Approximately 20-57% of NPH patients have comorbid Alzheimer's disease or other neurodegenerative conditions, which complicates diagnosis and may affect treatment outcomes 1
• An estimated 80% of NPH cases remain unrecognized and untreated, likely due to difficulty distinguishing NPH from other neurodegenerative disorders 4

Diagnostic Approach

MRI brain without IV contrast is the preferred initial imaging modality for NPH diagnosis, as it can identify all critical diagnostic features including the cerebral aqueduct flow void, which CT cannot detect. 2, 1

Imaging Findings

MRI (Preferred Modality)

• Ventriculomegaly not entirely attributable to cerebral atrophy or congenital enlargement 2
• Narrowed posterior callosal angle (<90°) 3, 2
• Effaced sulci along the high convexities with widened sylvian fissures 3
• Periventricular white matter changes indicating altered brain water content 3, 2
• Cerebral aqueduct flow void on MRI—a critical finding that CT cannot detect 3, 2
• Enlargement of temporal horns 2

CT Head Without IV Contrast (Alternative)

• CT can identify ventriculomegaly, narrowed posterior callosal angle, effaced sulci, and widened sylvian fissures 3
• Major limitation: CT cannot detect the cerebral aqueduct flow void and may miss small obstructing lesions that would indicate noncommunicating hydrocephalus 3
• CT is acceptable when MRI is contraindicated or unavailable 1

Additional Diagnostic Features

• Normal CSF pressure on lumbar puncture (despite the name, pressure may be normal or mildly elevated) 3, 4
• Communicating hydrocephalus on neuroimaging with no macroscopic obstruction of CSF flow 2
• Laboratory evaluation should include complete blood count, urinalysis, serum electrolytes, blood urea nitrogen, serum creatinine, fasting blood glucose, thyroid-stimulating hormone, and liver function tests to exclude reversible causes of cognitive impairment 1

Predictive Testing for Shunt Responsiveness

Clinical improvement following large-volume lumbar puncture (tap test) or prolonged external lumbar drainage reliably identifies patients likely to respond to shunt surgery, with properly selected patients having an 80-90% chance of responding. 2

• The tap test has high positive predictive value for therapeutic response 5
• Important caveat: A negative tap test does not exclude the possibility of treatment benefit 5
• Elevated aqueductal CSF stroke volume measured by phase-contrast MRI demonstrates high positive predictive value for shunt responsiveness in idiopathic NPH 2, 6
• When aqueductal CSF stroke volume is sufficiently elevated, there is excellent chance of shunt responsiveness with 100% positive predictive value in some studies 6

Differential Diagnosis Considerations

• Alzheimer disease presents primarily with progressive memory loss and cognitive decline without early prominent gait disturbance or urinary symptoms 1
• Lewy body dementia is characterized by visual hallucinations, Parkinsonian symptoms, and fluctuating cognition 1
• The presence of comorbid neurodegenerative disease in 20-57% of NPH patients means clinical findings and imaging studies often do not suffice to establish surgical indication alone 1, 4

Treatment

CSF diversion through ventriculoperitoneal shunting is the definitive treatment for NPH, with properly selected patients having an 80-90% chance of responding to surgery and all symptoms potentially improving. 2, 1

Surgical Outcomes

• Modern treatment leads to clinical improvement in 70-90% of treated patients 4
• All symptoms (gait, cognition, urinary incontinence) can potentially improve with shunting 2
• Serious complication rate is approximately 6% 2
• Gait stability and urinary incontinence show more significant improvement compared to cognitive decline 7

Surgical Risks and Complications

• Infection risk 7
• Need for shunt revision 7
• Over-drainage complications 7
• Despite these risks, current risk/benefit analyses indicate that shunt operations improve outcome compared to the spontaneous course of the disease 4

Timing of Treatment

• NPH should be treated at an early stage once diagnosis is confirmed 4
• The spontaneous course of NPH ends in dependence on nursing care for the vast majority of untreated patients 4

Emerging Therapies

• Minimally invasive endovascular CSF diversion systems (such as the eShunt System) are under investigation as alternatives to conventional ventriculoperitoneal shunting, potentially reducing risks associated with traditional shunting 7

Patient Selection Algorithm

1. Confirm clinical triad (particularly early gait disturbance) 1
2. Obtain MRI brain without IV contrast to identify characteristic imaging findings 2, 1
3. Perform lumbar puncture to confirm normal CSF pressure 3
4. Conduct tap test or external lumbar drainage to predict shunt responsiveness 2
5. Consider phase-contrast MRI to measure aqueductal CSF stroke volume for additional prognostic information 2, 6
6. Proceed with ventriculoperitoneal shunt placement in patients demonstrating positive predictive features 2, 1