Sensory Impairments, Alzheimer’s Disease, and Dementia

Alzheimer’s disease and other forms of dementia are associated with a number of sensory impairments. Hearing, vision, smell, touch, and taste can all be affected by such a disorder, resulting in disabilities that greatly reduce functioning. Researchers commonly focus on reducing the impact of sensory impairments as they arise, but another approach is to look for ways that they can be used to detect Alzheimer’s disease in its early stages.

The possibility of using sensory impairments as a “marker” to identify Alzheimer’s disease is enticing to medical professionals because it has proven very difficult to find reliable diagnostic methods to date. Currently, the most available means of detecting the early signs of dementia are cognitive evaluations, such as the SAGE exam on which the BrainTest® app is based. Ideally, professionals want to have reliable biological tests that they can use to confirm an early diagnosis, and studying sensory impairments may provide them with the means to do so.

Sensory Impairments and Dementia Risk

At the 70th Annual Meeting of the American Academy of Neurology in spring of 2018, researchers presented evidence that multisensory impairments are linked to a higher risk of developing dementia. The study included over 1,800 participants who were between the ages of 70 and 79 years old and did not have dementia at the beginning of the investigation. Their health records were tracked for a period of 10 years, with impairments in hearing, vision, smell, and touch being specifically tested during years 3 to 5.

The results showed that the risk of developing dementia increased significantly with the addition of each sensory impairment. Having just a single sensory impairment was associated with a 50% increase in risk, two impairments with a 100% increase, and three or four impairments with an increase of 280%. These rates were not dependent on the types of impairments involved, so, for example, having an auditory impairment would carry the same risk as having a visual impairment.

Potential Role in Alzheimer’s Detection

A new review published in Nature Reviews Neurology outlines existing research related to the potential role of sensory impairments as markers for identifying early-stage Alzheimer’s disease. According to the publication, evidence points to several forms of sensory impairment as having a potential connection to early-stage Alzheimer’s, especially those related to smell. Specific findings of interest include:

• Brain areas involved in the processing of smell (like the entorhinal cortex and olfactory bulb) show signs of damage very early in the progression of Alzheimer’s disease.
• The ability to identify and recall odors is commonly compromised in both people with Alzheimer’s and those who are at high risk of developing the disorder.
• Impaired odor identification is currently used to predict mild cognitive impairment (MCI).
• Hearing loss is associated with the future development of dementia and cognitive impairments.
• Visual changes that may indicate early Alzheimer’s disease include thinning of the retina, abnormal responses of the pupil to light, and impaired ability to discern contrast.

Future Research

Sensory impairments may come to play an important role in confirming Alzheimer’s disease and other dementias at an early stage in their development, perhaps even earlier than is possible by any current means of detection. These early results are promising, but more investigations will be needed to determine the best ways to put this approach into practice. In the meantime, we are now aware that people at an advanced age should not consider sensory impairments to be a natural effect of time, and their presence should instead serve as a source of motivation to be assessed for signs of dementia.