Patients’ subjective reports of changes in their sense of smell could also be useful in predicting conversion to dementia, according to a study from the Journal of the International Neurological Society.3 Researchers followed a sample of 1529 participants over a 10-year period. At baseline, they had normal overall cognitive functioning. Within the study period, 159 patients were diagnosed with dementia. The findings showed that participants who reported that their sense of smell was “worse than normal” had more than twice the odds of developing dementia than patients who reported a normal sense of smell.

“We think that people know that their sense of smell has gotten worse than before, and that is why they report that the sense of smell is ‘worse than normal,’” study co-author Jonas Olofsson, PhD, an associate professor of psychology at Stockholm University in Sweden, told Psychiatry Advisor. “Asking a simple question about the sense of smell might pick up on subtle changes, such as losing the ability to notice a certain spice in your spouse’s cooking, that might not be captured in smell tests.”


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Of course, not all people with early dementia have significant olfactory deficits, and though smell loss is common among the elderly, only a small number of elderly individuals develop dementia. “This means that in most cases, smell loss is not caused by dementia,” says Olofsson.

Such impairment can also be caused by other disorders. Recent findings reported in Psychiatry Research, for example, show that elderly patients with major depressive disorder (MDD) and patients with AD had worse scores on tests of olfactory memory than healthy controls.4 However, while the MDD patients showed impairments pertaining to both familiar and unfamiliar odors, the AD patients only had deficits in recognizing unfamiliar odors. Such distinctions illuminated by this study and others may prove useful in differential diagnosis when combined with other assessments.

“I think that olfactory tests can be used as part of dementia screening,” explains Olofsson. “That means that if you are shown to have a smell impairment that cannot be explained by infections, head trauma, or other conditions, and you also have additional risk factors, such as a family history of dementia, you might be monitored more carefully for signs of dementia than if your sense of smell was normal.”

This line of investigation could also lead to new treatment approaches. While there are currently no olfactory-based treatment methods, his research group and others are investigating whether training the sense of smell might improve brain functions. A more nuanced understanding of how dementia develops and presents differently in different patients could also enable clinicians to tailor more efficient treatment to the individual patient.

“Reduced odor identification ability may be one such clinical finding that could differentiate between individuals and aid in the decision making process” regarding a patient’s treatment, says Håberg.

Tori Rodriguez, MA, LPC, is a psychotherapist and freelancer writer based in Atlanta.

References

  1. Kjelvik G, et al. The brain structural and cognitive basis of odor identification deficits in mild cognitive impairment and Alzheimer’s disease. BMC Neurology. 2014; 14:168. 
  2. Conti MZ, et al. Odor identification deficit predicts clinical conversion from mild cognitive impairment to dementia due to Alzheimer’s disease. Archives of Clinical Neuropsychology. 2013; 28(5):391-9. 

  3. Stanciu I, et al. Olfactory impairment and subjective olfactory complaints independently predict conversion to dementia: a longitudinal, population-based study. Journal of the International Neurological Society. 2014; 20(2):209-17.
  4. Naudin M, et al. Long-term odor recognition memory in unipolar major depression and Alzheimer׳s disease. Psychiatry Research. 2014; 220(3):861-6.