Idiopathic Normal Pressure Hydrocephalus

Importance: Idiopathic normal pressure hydrocephalus (iNPH) is a progressive neurological disorder characterized by cerebral ventricular enlargement that is typically associated with gait impairment and often urinary dysfunction and cognitive decline in older adults. iNPH prevalence is approximately 1% to 4% among individuals 65 years and older and 6% to 8% among those 80 years and older. Observations: iNPH is a multifactorial disorder involving interactions among cerebrospinal fluid (CSF) circulation, vascular dysfunction, and white matter injury. Unlike secondary NPH, iNPH occurs without a known antecedent event such as subarachnoid hemorrhage. Gait disturbance, including a broad-based, slow, shuffling gait and impaired turning, occurs in 85% to 95% of patients with iNPH and is often the earliest symptom. Urinary dysfunction occurs in approximately 75% to 90% of patients with iNPH and commonly includes urgency, nocturia, urge incontinence, or leakage. Cognitive impairment is reported in 60% to 80% of patients with iNPH, predominantly involving impaired attention, processing speed, working memory, verbal fluency, and cognitive flexibility. iNPH is diagnosed primarily based on characteristic clinical findings and neuroimaging (typically brain magnetic resonance imaging) demonstrating cerebral ventricular and subarachnoid space enlargement. Although necessary for diagnosis, these neuroimaging findings are not reliably associated with response to treatment. Early diagnosis of NPH is important because shorter symptom duration and less advanced disease are associated with more favorable outcomes. Patients being evaluated for iNPH should undergo large-volume lumbar puncture with removal of 30 to 50 mL of CSF to confirm the diagnosis and predict shunt responsiveness, measured as improvement in objective gait measures starting within hours after drainage. Extended lumbar drainage with removal of 200 to 300 mL of CSF over several days in an inpatient setting provides higher prognostic accuracy, and may be performed in patients with high clinical suspicion and a negative or equivocal clinical response to lumbar puncture. Treatment for iNPH is CSF diversion with shunt placement, most commonly performed with ventriculoperitoneal shunts, although ventriculoatrial and lumboperitoneal shunts may have similar efficacy. After shunting, approximately 75% to 80% of patients have gait velocity improvement; cognitive and urinary improvements occur in approximately 50% to 70%. Complications of shunts include overdrainage and underdrainage (10%-30%), presenting as postural headaches and subdural collections, and recurrence or worsening of iNPH symptoms, shunt malfunction (10%-20%), and shunt infections (<1%-2%). Conclusions and Relevance: iNPH affects approximately 1% to 4% of adults 65 years and older and is associated with gait impairment, cognitive decline, and urinary dysfunction. Symptoms improve in approximately 70% to 90% of patients with iNPH who undergo shunt surgery.