What is the diagnosis and treatment approach for a patient with suspected Normal Pressure Hydrocephalus (NPH)?

Normal Pressure Hydrocephalus: Diagnosis and Treatment

For suspected NPH, obtain MRI brain without IV contrast as your first imaging study, look for the classic triad of gait disturbance (especially "magnetic" feet), cognitive impairment, and urinary incontinence, and if confirmed with supportive imaging findings, proceed to CSF tap test or external lumbar drainage to predict shunt responsiveness before definitive ventriculoperitoneal shunt placement. 1, 2, 3

Clinical Presentation: What to Look For

The diagnostic approach begins with recognizing the characteristic clinical pattern:

• Gait disturbance occurs first in approximately 70% of patients and is the cardinal sign—specifically look for a hypokinetic gait where the feet appear "glued to the floor" or "magnetic" 1, 2
• Cognitive impairment develops later, manifesting as frontal lobe symptoms: psychomotor slowing, deficits in attention, working memory, verbal fluency, and executive function—not the progressive memory loss typical of Alzheimer's disease 1, 3
• Urinary incontinence completes the triad, presenting as bladder detrusor dysfunction 4

Critical pitfall: Patients typically present late in the disease course due to slow, gradual symptom onset, and approximately 75% of patients with NPH severe enough to require treatment also have another neurodegenerative disorder (Alzheimer's, Lewy body dementia), making diagnosis challenging 3, 5

Initial Diagnostic Workup

Imaging Studies

MRI brain without IV contrast is the preferred initial test because it identifies multiple characteristic features simultaneously 1, 2, 3:

• Ventriculomegaly not entirely attributable to cerebral atrophy
• Narrowed posterior callosal angle (<90°)
• Effaced sulci with widened sylvian fissures
• Periventricular white matter changes
• Critical finding: Cerebral aqueduct flow void (indicates hyperdynamic CSF flow and predicts shunt responsiveness) 2, 6
• Disproportionately enlarged subarachnoid-space hydrocephalus (DESH) pattern 3
• Enlargement of temporal horns 2

If MRI is contraindicated or unavailable, CT head without IV contrast can identify ventriculomegaly, narrowed callosal angle, effaced sulci, and widened sylvian fissures, though it is less sensitive 1, 3

Laboratory Evaluation

Obtain these tests to exclude reversible causes of cognitive impairment 1, 3:

• Complete blood count
• Urinalysis
• Serum electrolytes, BUN, creatinine
• Fasting blood glucose
• Thyroid-stimulating hormone (exclude hypothyroidism)
• Liver function tests
• Vitamin B12 level (exclude B12 deficiency)

Predictive Testing for Surgical Candidacy

Do not proceed directly to shunt surgery based on clinical and imaging findings alone—semi-invasive diagnostic procedures are recommended to predict shunt responsiveness 5:

CSF Tap Test (First-Line Predictive Test)

• Large-volume lumbar puncture (30-50 mL CSF removal) with pre- and post-tap gait assessment reliably identifies patients likely to respond to shunt surgery 2
• Important limitation: Single CSF tap test has low sensitivity, so a negative result cannot exclude patients from surgery 7

If Initial Tap Test is Negative but Clinical Suspicion Remains High

Proceed to one of these options 7:

• Repeated CSF tap tests (RTT): Multiple large-volume LPs over several days
• Continuous external lumbar drainage (LED): 3-5 days of continuous CSF drainage with daily clinical assessments

Advanced Predictive Testing

• Phase-contrast MRI measuring aqueductal CSF stroke volume demonstrates high positive predictive value for shunt responsiveness in idiopathic NPH 2
• Intracranial pressure monitoring: B-waves occurring during >50% of recording time, combined with positive RTT or LED, provides the most reliable prediction 7

Definitive Treatment

Ventriculoperitoneal shunt placement is the definitive treatment 1, 2:

• Properly selected patients using contemporary diagnostic tests have an 80-90% chance of responding to shunt surgery 2, 5
• All three symptoms (gait, cognition, urinary) can potentially improve 2
• Serious complication rate is approximately 6% 2
• Treatment should be initiated early once diagnosis is confirmed, as the spontaneous course leads to nursing care dependence in the vast majority of untreated patients 5

Key Differential Diagnoses to Exclude

• Alzheimer disease: Progressive memory loss and cognitive decline without early prominent gait disturbance or urinary symptoms 1
• Lewy body dementia: Visual hallucinations, Parkinsonian symptoms, and fluctuating cognition 1
• Other considerations: Positional orthostatic tachycardia syndrome, cervicogenic headaches, migraines (if symptoms persist after negative workup) 8

Clinical Context

NPH affects approximately 3.7% of patients over 65 years and represents one of the few potentially reversible causes of dementia, yet approximately 80% of cases remain unrecognized and untreated 1, 3, 5