New smell test that could let doctors spot dementia even earlier
A SCAN that tests a person’s sense of smell could detect the early signs of Alzheimer’s disease before any memory loss develops.
The ability to smell deteriorates in many neurological conditions, from Down’s syndrome and schizophrenia to Alzheimer’s and Parkinson’s disease.
But existing tests – including one that asks patients to sniff out peanut butter from a distance – offer an incomplete picture, according to scientists at Harvard Medical School and Massachusetts General Hospital.
The researchers say such ‘sniff tests’ monitor the sense of smell only after it has been processed by the brain.
They have developed a scan which tracks a radioactive molecule that is injected into the body and accumulates in neurons in the nose.
The scan, called Neuroflux, picks up changes in the number of these neurons – a decrease indicating a decline in sense of smell – and avoids the need for a painful biopsy or MRI scans, with which it is difficult to be accurate in the nose.
The breakthrough, found to work effectively in mice, is hoped to lead to a test for all kinds of memory loss, and not just that caused by Alzheimer’s.
Lead author Dr Jacob Hooker said: ‘I heard about the peanut test for Alzheimer’s years ago. A lot of beautiful research with smell tests has been published with many geared towards making them more robust, but there are lots of reasons that might not work very well, for example if someone has sinus inflammation due to a cold.
‘By looking more directly at olfactory sensory neurons between the nose and brain, we can learn more about the health of the cells that are responsible for smell and extend into the brain.
‘This may provide a window into the brain and we hope this will ultimately help with early diagnosis.’
These links between the nose and the brain explain why memories are more strongly triggered by a smell than by a photo. In many patients, a partial or complete loss of smell happens before cognitive problems in Alzheimer’s and years before the tremors and loss of motor function caused by Parkinson’s disease.
The researchers, whose study was published in the Journal of Clinical Investigation, said their scan was better than sniff tests because it identifies initial problems with odour detection and not just the higher-level processing of smells in the brain.
Biopsies show whether olfactory sensory neurons have been lost, but are painful, technically difficult and may miss the area where neurons are being lost.
MRI scans can be used to visualise the tissue but can be challenging as they detect water in the tissue, not neurons directly, and there is very little water in the nose.
The new scan is hoped to hold the answer. If the radioactive molecule’s signal reduces in the few months between two scans, this is a sign that there are fewer olfactory neurons.
Claire Bale, of Parkinson’s UK, said: ‘A test like this could be a significant step forwards for diagnosing the condition earlier when people are most likely to benefit from new treatments that aim to slow, stop or reverse its damage.’
Dr Doug Brown, of the Alzheimer’s Society, said: ‘There is evidence to suggest that someone’s sense of smell could be impacted in the early stages of dementia.’
But he added: ‘Because this method has only been tested in animals and not humans, it is too early to tell if it could help improve diagnosis.’
‘Window into the brain’