Normal Pressure Hydrocephalus
Normal pressure hydrocephalus (NPH) is a neurological condition characterized by an abnormal accumulation of cerebrospinal fluid (CSF) in the brain’s ventricles, causing them to enlarge despite normal or intermittently elevated CSF pressure. This enlargement compresses surrounding brain tissue, leading to a classic triad of symptoms: gait disturbance, cognitive impairment, and urinary incontinence. NPH primarily affects older adults and is one of the few reversible causes of dementia, making early diagnosis and treatment crucial for optimal outcomes.
What is it?
Normal pressure hydrocephalus occurs when cerebrospinal fluid—the clear fluid that cushions the brain and spinal cord—accumulates in the brain’s ventricles (fluid-filled spaces), causing them to expand beyond their normal size. Unlike other forms of hydrocephalus where CSF pressure is consistently elevated, NPH is characterized by normal or only intermittently elevated pressure measurements during lumbar puncture. The condition develops due to impaired CSF absorption rather than overproduction, though the exact mechanisms remain incompletely understood. As CSF accumulates, the enlarged ventricles compress adjacent brain tissue, particularly affecting regions involved in motor control, cognition, and bladder function.
NPH is classified into two types: idiopathic NPH, which occurs without an identifiable cause and accounts for the majority of cases, typically affecting adults over 60; and secondary NPH, which develops following a known event such as subarachnoid hemorrhage, meningitis, traumatic brain injury, or brain surgery. The condition progresses gradually over months to years, with symptoms often mistaken for normal aging, Alzheimer’s disease, or Parkinson’s disease. Risk factors include advanced age, history of brain hemorrhage or infection, and possibly cardiovascular disease. The hallmark of NPH is that it represents one of the few potentially reversible causes of dementia—surgical treatment can significantly improve symptoms, particularly if diagnosed and treated early.
Important to Know
NPH classically presents with a triad of symptoms that typically appear in a characteristic sequence. Gait disturbance usually appears first and is often the most prominent feature—patients develop a shuffling, broad-based, magnetic gait (as if feet are stuck to the floor), difficulty initiating walking, slow speed, and increased fall risk. Cognitive impairment follows, manifesting as slowed thinking (bradyphrenia), difficulty with attention and concentration, memory problems, executive dysfunction, and apathy or personality changes. Urinary symptoms develop last, including urgency, frequency, and eventual incontinence. Not all patients exhibit the complete triad. Diagnosis requires brain imaging (MRI or CT) showing enlarged ventricles out of proportion to brain atrophy, clinical symptoms consistent with NPH, and confirmation through diagnostic testing such as the “tap test” (large-volume lumbar puncture) where temporary symptom improvement after CSF removal predicts good surgical outcomes. Additional tests may include CSF infusion studies or extended lumbar drainage. Treatment involves surgical placement of a ventriculoperitoneal (VP) shunt, which diverts excess CSF from the brain ventricles to the abdominal cavity where it can be absorbed. Shunt surgery is successful in improving symptoms in 50-80% of carefully selected patients, with gait improvement typically most dramatic, followed by cognitive and urinary symptoms. Best outcomes occur when treatment is initiated early before irreversible brain damage occurs. Complications can include shunt malfunction, infection, over-drainage causing headaches, or subdural hematomas. Regular follow-up is essential to monitor shunt function and symptom response.