Alzheimer’s disease and loss of smell

Anosmia (loss of smell) or hyposmia (hyposmia) can be an early and important sign of Alzheimer’s disease before other symptoms begin. The degree of olfactory loss may correlate with an increased risk of developing Alzheimer’s disease. Anosmia can be exacerbated as the disease progresses from early mild cognitive impairment to Alzheimer’s disease.

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Alzheimer’s disease is the most common form of dementia in the world. At the heart of pathology is the atrophy (contraction) of the hippocampus and cortex caused by the loss of the brain, especially nerve cells and synapses. Nerve cell loss is caused by the accumulation of amyloid beta plaque and neurofibrillary tangles of hyperphosphorylated tau (two important pathological features of Alzheimer’s disease).

Symptoms of Alzheimer’s disease become apparent as the disease progresses, but early detection may be important to delay the disease, especially in the continuous development of new treatments and better management of the disease from an early stage. There is. However, the problem is that early detection (biomarkers) is limited or difficult to assess in the clinic, and a definitive diagnosis can only be made after extensive clinical, neuroimaging, pathology, and postmortem analysis. It means that you can do it.

Loss of smell in Alzheimer’s disease

According to an American study, older people with olfactory dysfunction (hyposmia) (about 3000 people aged 57-85) are more likely to develop dementia within 5 years, regardless of other risk factors. It turns out that there are more than twice as many. People with the worst odor discrimination (complete anosmia) were most likely to develop dementia within 5 years. The degree of olfactory dysfunction was correlated with the severity of dementia that occurred. That is, mild cognitive impairment and minor disorders associated with healthy controls, and advanced disorders associated with Alzheimer’s disease.

Of all those evaluated, 4.1% were diagnosed with dementia within the next 5 years, and 47% had olfactory dysfunction on the first assessment. This was in contrast to 80% of all assessed individuals who had normal olfactory function who did not develop dementia within 5 years. In addition, a meta-analysis of 39 studies showed that a large effect size (Cohens d = 1.73) was reported between olfactory loss and Alzheimer’s disease, especially between MCI and Alzheimer’s disease with respect to olfactory loss. There is a high degree of non-uniformity.

Olfaction loss is often not considered the main symptom of Alzheimer’s disease, but it is one of the earliest symptoms (if it does occur) in patients. Loss of odor alone is not a sufficient sign of Alzheimer’s disease, especially in the early stages of Parkinson’s disease, multiple sclerosis, amyotrophic lateral sclerosis, Huntington’s disease, and many other neurological conditions. It is also important to note. disease.

If possible, the development of disease-specific odor tests is essential to distinguish between diseases (further research is needed at this stage). Nevertheless, olfactory loss is an important symptom that occurs in a variety of neurological conditions (as explained). Therefore, if an odor test shows a disorder, it is important to perform a standard test such as the MMSE along with neuroimaging as a powerful way to assess the early stages of Alzheimer’s disease.

In addition, hyposmia (dysosmia) can also result from normal aging, but the degree of hyposmia or anosmia, especially earlier than expected as part of normal aging, is within a few people. It is a powerful indicator of an increased likelihood of developing dementia in the first few years of the onset of such symptoms – before significant cognitive impairment begins to occur.

What Causes Alzheimer’s Disease to Cause Olfactory Loss?

Just as amyloid plaques and neurofibrillary tangles contribute to the loss of nerve cells and synapses in the brain itself, they are also thought to be responsible for olfactory dysfunction. Neuropathology is thought to occur in areas such as the olfactory system prior to disorders in the hippocampus and cortex. In addition, the olfactory system is more vulnerable to Alzheimer-related damage due to its limited self-healing mechanism.

Based on these findings, a simple discriminative odor test may be able to assess the risk of Alzheimer’s disease (or other neurological condition) before the symptoms of the disease begin to appear. These can be verified by other diagnostic tools such as laboratory tests, biomarkers and neuroimaging. Early identification can lead to improved prognosis and early intervention that is likely to implement a long-term plan.

In summary, olfactory loss may be an early important biomarker of Alzheimer’s disease that occurs before significant cognitive impairment begins. People who lose their sense of smell in middle age are more likely to develop Alzheimer’s disease within 10 years, and those who have the most olfactory deficits (complete loss) are at greatest risk. Therefore, odor discrimination tests can be a simple and effective means of assessing the likelihood of developing Alzheimer’s disease and enabling early intervention and management planning.

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