Can NPH Patients Have Normal Opening CSF Pressure?
Yes, patients with Normal Pressure Hydrocephalus (NPH) characteristically have normal opening CSF pressure on lumbar puncture—this is a defining feature of the condition, not an exception. 1
Understanding the Paradox of "Normal Pressure" in NPH
The term "Normal Pressure Hydrocephalus" itself reflects this clinical reality:
Single-point lumbar puncture measurements typically show normal or only mildly elevated CSF pressure values (within the 6-25 cmH₂O range), but this represents only a momentary snapshot that misses intermittent pressure elevations. 1
Case reports confirm that NPH patients present with normal opening pressures—for example, documented cases show opening pressures of 18 mmHg (approximately 24 cmH₂O), which falls within the normal adult range. 2
The normal CSF pressure finding occurs despite clear ventriculomegaly and the classic clinical triad of gait disturbance, cognitive impairment, and urinary incontinence. 2, 3
Why This Occurs: The Pathophysiology
The "normal" pressure reading is misleading because:
CSF pressure is dynamic, not static—continuous monitoring reveals intermittent pressure elevations that single measurements cannot capture. 4
The underlying problem in NPH is reduced conductance to CSF outflow (Cout), not sustained elevated pressure. 5
Patients can have normal mean intracranial pressure while still experiencing pathological CSF dynamics that cause ventricular enlargement and neurological symptoms. 5, 6
Clinical Implications for Diagnosis
When evaluating suspected NPH:
Do not exclude NPH based on normal opening pressure—this finding is expected and consistent with the diagnosis. 1, 2
Focus on the combination of clinical triad, ventriculomegaly disproportionate to atrophy (Evans index >0.3), and response to large-volume CSF tap test rather than the absolute pressure value. 2, 7
Multiple or prolonged CSF pressure recordings in NPH patients are invariably within normal ranges, which can hamper correct diagnosis if clinicians expect elevated pressures. 6
Common Pitfall to Avoid
The most critical error is dismissing NPH as a diagnosis because the opening pressure is normal. This misunderstands the fundamental nature of the condition—the "normal pressure" designation refers to the characteristic finding of normal CSF pressure measurements despite symptomatic hydrocephalus. 1, 3 The condition should instead be suspected when patients present with the clinical triad and appropriate imaging findings, regardless of CSF pressure readings.