Lumbar puncture could replace questions in dementia diagnosis

Patients suspected to have dementia could soon undergo a lumbar puncture procedure to get a clear diagnosis. The proposals, set out by the health watchdog NICE, are controversial as the spinal tap is known to be painful and can have side effects.

At present, dementia is tested using a series of memory questions, but this method allows room for uncertainty. It is hoped that a clearer picture could be obtained using a lumbar puncture, leading to earlier diagnosis and in turn, better treatment.

Drawing spinal fluid from a patient using a needle is a delicate procedure and can lead to headaches and infections. Experts have admitted to being nervous about the move, but with as many as one in ten dementia tests having unclear results, it could lead to a conclusive answer.

Among the questions on the current dementia test are the name of the current prime minister and the date. Practical exercises also include asking patients to accurately draw the time onto a blank clock face.

If the signs are mixed at the end of the test, doctors are instructed to order a brain scan that should highlight any change in activity levels. Draft guidelines from NICE suggest that in future, medics will be told to carry out a lumbar puncture instead, with the fluid then checked for tau and amyloid-beta proteins, which has both been linked to dementia.

While this process would be cheaper for the NHS than a brain scan and potentially more accurate than the question-based tests, there are some concerns. As well as the side effects, there are a number of types of dementia that are not associated with the two proteins that the fluid is screened for and could therefore go undetected.

John O’Brien, professor of psychiatry at Cambridge University, addressed an audience at the Dementias 2018 conference in London recently. He highlighted the fact that vascular and Lewy body dementia could be missed using the spinal tap method.

Although these two types of dementia are less common than Alzheimer’s, they still account for up to 40 per cent of cases. He also said that, unlike brain scans, lumbar punctures do not show which parts of the brain are affected or to what extent.

Another view, which has been expressed by Dr Matthew Jones of Manchester University, is that invasive tests are hard to justify when there is no cure for dementia. Many dementia charities take the view that diagnosis is vital, however, so that what treatment and support is available can be administered.

Currently, a third of dementia sufferers do not have a formal diagnosis, meaning they may be missing out on services that would help them. The new NICE guidelines are not due out until June and, unless the wording is changed, will state that doctors should offer lumbar puncture tests and scans.

It is thought that by putting the spinal tap option first, medics will assume that this is the preferred option. If you have a relative who is a borderline case for dementia, it’s something to be aware of.