Diagnosis of Normal Pressure Hydrocephalus
For an older adult presenting with the classic triad of gait disturbance, cognitive decline, and urinary incontinence, obtain MRI brain without IV contrast as the first-line diagnostic test to identify characteristic NPH features including ventriculomegaly, narrowed posterior callosal angle, and DESH pattern. 1, 2, 3
Clinical Recognition
The diagnostic approach begins with recognizing the characteristic symptom progression:
- Gait disturbance appears first in approximately 70% of patients, manifesting as a hypokinetic, "magnetic" gait where feet appear glued to the floor 3, 4
- Cognitive impairment develops later, characterized by frontal lobe dysfunction including psychomotor slowing, deficits in attention, working memory, verbal fluency, and executive function—not primarily memory loss 2, 3
- Urinary incontinence occurs as the third component of the triad, though not all patients present with complete symptoms 3, 5
This temporal sequence is critical: if memory loss dominates early without prominent gait disturbance, consider Alzheimer's disease instead 3. If visual hallucinations and fluctuating cognition are present, suspect Lewy body dementia 3.
Imaging Studies
MRI brain without IV contrast is the gold standard imaging modality recommended by the American College of Radiology 1, 2, 3:
- Identifies ventriculomegaly with narrowed posterior callosal angle 1, 3
- Demonstrates effaced sulci with widened sylvian fissures 1, 3
- Shows periventricular white matter changes and cerebral aqueduct flow void 1, 6
- Reveals the disproportionately enlarged subarachnoid-space hydrocephalus (DESH) pattern 1
If MRI is contraindicated or unavailable, CT head without IV contrast serves as an acceptable alternative to identify ventriculomegaly, narrowed posterior callosal angle, effaced sulci, and widened sylvian fissures 1, 3.
Hyperdynamic CSF flow through the aqueduct on phase-contrast MRI predicts excellent shunt responsiveness, with 100% positive predictive value in some studies 6.
Laboratory Evaluation
The American Heart Association recommends obtaining the following laboratory tests 1:
- Complete blood count
- Urinalysis
- Serum electrolytes, blood urea nitrogen, serum creatinine
- Fasting blood glucose
- Thyroid-stimulating hormone
- Liver function tests
These tests exclude reversible causes of cognitive impairment such as B12 deficiency, hypothyroidism, and metabolic derangements 7.
Predictive Testing for Surgical Candidacy
When imaging supports NPH but you need to predict shunt responsiveness:
- CSF tap test (removing 30-50 mL of CSF) with documented gait improvement within 18-24 hours strongly predicts surgical benefit 8, 4, 5
- A single tap test has low sensitivity, so negative results do not exclude patients from surgery 8
- For equivocal single tap tests, proceed to repeated CSF tap test (RTT) or continuous lumbar external drainage (LED) 8, 5
- The most reliable prediction combines positive RTT or LED with B-waves present during >50% of intracranial pressure monitoring time 8
Critical Diagnostic Pitfalls
Comorbidity with other neurodegenerative diseases occurs in 20-57% of NPH patients, particularly Alzheimer's disease 2, 3. The American College of Radiology notes that approximately 75% of NPH patients severe enough to require treatment also have another neurodegenerative disorder 1. This overlap complicates diagnosis but should not exclude patients from shunting if CSF drainage produces improvement 5.
NPH affects 3.7% of patients over 65 years and represents one of the few potentially reversible causes of dementia 1, 3. Any patient showing improvement after CSF drainage deserves therapeutic intervention with ventriculoperitoneal shunting, which offers 80-90% response rates in properly selected patients 3, 5.
Patients with secondary NPH (known history of meningitis or hemorrhage) respond better to shunting than those with idiopathic NPH 8, 6.