Normal Pressure Hydrocephalus (NPH)

NPH can happen for different reasons. In many patients, there's no clear identifiable cause, called idiopathic NPH. In other patients, NPH may occur secondary to a previous neurological condition:

• Idiopathic NPH is the most common form in older adults. The exact mechanism is unknown but likely involves impaired CSF absorption.
• Secondary NPH may occur following subarachnoid haemorrhage, meningitis, head trauma, or previous brain surgery. Scar tissue impairs CSF flow and absorption.

Gait Disturbance

Patients develop a characteristic shuffling, magnetic gait – taking small steps with their feet almost seeming to stick to the floor. Starting to walk can be hard, and the feet may not lift properly off the ground. This is usually the symptom that responds best to treatment.

Cognitive Impairment

People with NPH often become slower in their thinking and have trouble concentrating, planning, or organising tasks. Unlike Alzheimer's disease, language is typically not affected early on. People may seem slowed down or less motivated. These changes usually come on gradually.

Urinary Incontinence

Urinary urgency and incontinence develop, typically after the gait and cognitive symptoms. Patients often have difficulty getting to the toilet in time due to both the gait disturbance and loss of bladder inhibition.

Diagnosis of NPH can be difficult because symptoms can look like several other conditions. A combination of clinical assessment, imaging, and CSF removal tests is used to help make the diagnosis:

• Brain scan (MRI or CT) – this shows whether the fluid-filled spaces in the brain are both enlarged and have a morphology consistent with NPH. Large Sylvian fissures and tight convexity sulci are characteristic imaging features of NPH
• Tap test (lumbar puncture) – around 30mL of fluid is removed from the spine. An improvement in cognition and gait predicts a positive outcome from shunt surgery
• Extended fluid drainage trial – for some patients, an extended period of fluid drainage may be beneficial. A small tube is left in place for 2 – 3 days to drain fluid, with constant assessment of its effect. 

Neuropsychological assessment, neurological examination, and a multidisciplinary team approach are important in confirming the diagnosis.

Ventriculoperitoneal (VP) Shunt

Surgical insertion of a VP shunt is the standard treatment for NPH. A thin tube is inserted into the fluid-filled space in the brain through a small opening in the skull. This is then connected to a valve and tunnelled under the skin down to the abdomen, where the excess fluid can be absorbed by the body. Modern shunts have an adjustable valve, meaning the amount of drainage can be fine-tuned after surgery without needing another operation.

Gait is the symptom most likely to improve following surgery and improvements may be dramatic. Cognitive and continence symptoms may also improve, though to a lesser degree and more slowly. Having surgery earlier, before symptoms become severe or long-standing, tends to lead to better results.