Alzheimer’s Therapy Boosts Cognition of People Who Lost Smell but Lack Signs of the Disease

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by Ana Belo |

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Alzheimer's and smell

Some people lose their sense of smell before they begin developing Alzheimer’s disease.

New York researchers decided to treat older people who had lost their sense of smell and who had mild cognitive impairment for Alzheimer’s before signs of the disease showed up. The treatment led to improvement in their cognitive abilities.

The researchers were from Columbia University Medical Center and the New York State Psychiatric Institute. The study they published online in the Journal of Alzheimer’s Disease was titled “Change in Odor Identification Impairment is Associated with Improvement with Cholinesterase Inhibitor Treatment in Mild Cognitive Impairment.

Loss of smell is an early sign of decreasing cognitive ability, studies have shown. And decreasing cognitive ability is an important risk factor for Alzheimer’s.

The researchers wanted to see if people with mild cognitive impairment who had lost their sense of smell would respond to the cholinesterase inhibitors that doctors use to treat Alzheimer’s.

Alzheimer’s patients have impaired nerve cell communication. Scientists call the communication cholinergic function because cholinergic neurons are the nerve cells that use the neurotransmitter acetylcholine to communicate. Low levels of acetylcholine inhibit the communication.

Cholinesterase inhibitors prevent an enzyme from breaking down acetylcholine. This keeps acetylcholine at higher levels in the neurons and for longer periods. Blocking this enzyme increases nerve cell communication in the brain.

The researchers used the cholinesterase inhibitor donepezil in their study.

“We know that cholinesterase inhibitors can make a difference for Alzheimer’s patients, so we wanted to find out if we could identify patients at risk for Alzheimer’s who might also benefit from this treatment,” Dr. D.P. Devanand, a Columbia University Medical Center psychiatry professor, said in a press release. “Since odor identification tests have been shown to predict progression to Alzheimer’s, we hypothesized that these tests would also allow us to discover which patients with MCI [mild cognitive impairment] would be more likely to improve with donepezil treatment,” said Devanand, the study’s lead author.

Cholinesterase inhibitors have improved Alzheimer’s patients’ cognitive symptoms, but have had limited success treating mild cognitive impairment.

The team wanted to know if treating patients who had lost their sense of smell with donepezil would improve their cognition.

Researchers gave 37 participants smell, memory and cognitive-function tests at three points — just before treatment started, and at weeks 26 and 52.  The team started patients on 5 mg of donepezil a day, and increased the nasal spray to 10 mg a day if patients could tolerate it. The smell test they used was the University of Pennsylvania Smell Identification Test.

Donepezil led to considerable improvement in patients’ cognitive function, the researchers discovered. The improvement began showing up in some as early as eight weeks after treatment began.

“These results, particularly if replicated in larger populations, suggest that these simple inexpensive strategies have the potential to improve the selection of patients with mild cognitive impairment who are likely to benefit from treatment with cholinesterase inhibitors like donepezil,” Devanand said.