Normal pressure hydrocephalus can cause dementia, and is one of the few causes of dementia that can potentially be reversible. The condition is progressive and shortens lifespan if untreated.
Normal pressure hydrocephalus is sometimes imprecisely referred to as “water on the brain”. Within the brain are spaces called ventricles that carry cerebrospinal fluid throughout the brain and connect to the spinal canal. When the cerebrospinal fluid cannot drain normally from the ventricles, the ventricles enlarge. This enlargement causes pressure on the brain surrounding the ventricles, which leads to neurologic symptoms.
Normal pressure hydrocephalus is typically thought of as a gait disorder that has two other associated features- cognitive dysfunction and urinary dysfunction. The gait difficulty tends to include slow, short, and shuffling steps, and there may be problems with initiating walking. The feet may feel like they are stuck to the ground. Turning around and maneuvering in and out of cars also become less fluid. The cognitive symptoms tend to include a slowness in thinking, decline in attention, and executive dysfunction. Memory may seem affected but the person may tend to respond well to hints jogging their memory. The urinary problems are often urge incontinence, meaning that the person does feel the urge to urinate but they cannot make it to the bathroom in time to prevent an accident.
Normal pressure hydrocephalus is treated surgically. A shunt is inserted into the ventricles and drains the cerebrospinal fluid into another part of the body, typically the peritoneal cavity of the abdomen. With the removal of the fluid and pressure buildup in the ventricles, the neurologic symptoms can improve or even resolve.
Unfortunately, not everyone has an improved outcome after surgical treatment of normal pressure hydrocephalus. There can be many reasons for this:
Sometimes the wrong patient is selected for treatment. This happens when:
- Brain imaging is misinterpreted as showing hydrocephalus when in fact the ventricular enlargement was just due to the brain itself shrinking (due to normal aging or another type of dementia different from normal pressure hydrocephalus).
- Normal pressure hydrocephalus is diagnosed when in fact the person’s dementia is due to another cause, such as Alzheimer’s disease, vascular dementia, mixed dementia, dementia with Lewy bodies, or another type of dementia.
- The person has both normal pressure hydrocephalus and another cause for dementia. Treatment of the normal pressure hydrocephalus will not reverse the other cause for dementia that does not have a surgical treatment option.
- Normal pressure hydrocephalus has been present untreated for too long, and despite surgical treatment the symptoms are no longer reversible.
Sometimes the right patient is selected for treatment, but the treatment results in complications.
- Shunt infection can occur, and may even require a surgery to remove the shunt temporarily before replacing it.
- Bleeding complications can occur, such as subdural hematoma.
There are procedures that can help figure out if a person is likely to respond to surgical treatment of normal pressure hydrocephalus. These include a high/large volume lumbar puncture, also known as a high/large volume spinal tap, and a lumbar drain trial. Although these types of evaluations can help, they are not perfect in determining who should proceed to shunt surgery.
Diagnosing dementia due to normal pressure hydrocephalus and deciding whether or not to undergo surgical treatment is very challenging. A comprehensive evaluation is important for trying to prevent delays in referral to neurosurgery as well as for avoiding unnecessary surgeries, both of which could do harm.
References and Resources
- Andren, K, Wikkelso, C, Sundstrom, N, Israelsson, H, Agerskov, S, Laurell, K, Hellstrom, P, & Tullberg, M. (2020). Survival in treated idiopathic normal pressure hydrocephalus. J Neurol, 267(3), 640-648. doi:10.1007/s00415-019-09598-1