Normal Pressure Hydrocephalus: Diagnosis and Treatment
Diagnostic Approach
MRI brain without IV contrast is the first-line imaging modality for diagnosing NPH, and should be obtained immediately in any older adult presenting with the classic triad of gait disturbance, cognitive impairment, and urinary incontinence. 1, 2
Clinical Presentation Recognition
The cardinal feature that should trigger NPH evaluation is gait disturbance, which occurs first in approximately 70% of patients and manifests as a hypokinetic, "magnetic" gait where feet appear glued to the floor 2, 3. This gait abnormality typically precedes other symptoms by months to years 1, 4.
The complete clinical triad includes:
- Gait disturbance: Hypokinetic, magnetic gait with postural instability 2, 3
- Cognitive impairment: Frontal lobe symptoms including psychomotor slowing, deficits in attention, working memory, verbal fluency, and executive function—not primarily memory loss 2
- Urinary incontinence: Urgency, frequency, and incontinence 2, 3
Critical caveat: Only 25-50% of NPH cases present with the complete classic triad; atypical or incomplete presentations are common and should not exclude the diagnosis 5.
Imaging Findings
MRI without IV contrast identifies characteristic NPH features 1, 2:
- Ventriculomegaly with narrowed posterior callosal angle
- Effaced sulci at the vertex with widened sylvian fissures
- Periventricular white matter changes (FLAIR hyperintensities)
- Cerebral aqueduct flow void on T2 sequences
- Disproportionately enlarged subarachnoid-space hydrocephalus (DESH) pattern
If MRI is contraindicated, CT head without IV contrast is acceptable but less sensitive 1, 2.
Laboratory Evaluation
Obtain 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 such as B12 deficiency, hypothyroidism, and metabolic derangements 2.
Red Flags Requiring Alternative Diagnosis
If severe headaches accompany rapid functional decline, urgently exclude subdural hematoma, cerebral venous thrombosis, obstructive hydrocephalus, and spontaneous intracranial hypotension before proceeding with NPH workup. 6 Recent head trauma, cancer history, or anticoagulation use mandate immediate investigation for these alternative diagnoses 6.
Predictive Testing for Surgical Candidacy
After confirming NPH imaging pattern, perform large-volume lumbar puncture (CSF tap test) removing 30-50 mL of CSF to predict shunt responsiveness. 5, 3 Transient improvement in gait within 18-24 hours following CSF removal strongly predicts surgical benefit 5, 3.
Algorithm for Equivocal Cases
- Single CSF tap test positive (gait improvement observed): Proceed to shunt surgery 5
- Single CSF tap test negative: Perform repeated CSF tap tests (RTT) or continuous lumbar external drainage (LED) for 3-5 days 5
- RTT or LED positive + B-waves present >50% of ICP recording time: Highest prediction of surgical success 5
- All testing negative but strong clinical suspicion: Any patient showing improvement after CSF drainage deserves therapeutic intervention, even with coexisting neurodegenerative disease 4
Treatment
Ventriculoperitoneal shunt placement is the definitive treatment for NPH, with properly selected patients having an 80-90% chance of responding to surgery. 2 The shunt drains excess CSF and can reverse neurological dysfunction, improving gait, cognition, and urinary symptoms 2, 6, 3.
Timing Considerations
While evidence is inconclusive regarding optimal surgical timing, most studies suggest clinical improvement occurs after VP shunting regardless of symptom duration, though some data indicate better outcomes with shorter preoperative symptom duration 7. Do not delay shunt surgery once diagnosis is confirmed and predictive testing is positive, as NPH represents one of the few reversible causes of dementia, affecting 3.7% of adults over 65 years 1, 2.
Comorbidity Management
Approximately 20-57% of NPH patients have coexisting Alzheimer's disease or other neurodegenerative conditions 2. This comorbidity should not exclude patients from shunt surgery if they demonstrate improvement with CSF drainage testing 4. The presence of other neurodegenerative diseases does not preclude benefit from shunt placement in appropriately selected patients 4.