Unexpected sign of Alzheimer"s and Parkinson"s diseases discovered by scientists

Loss of smell: an alarming signal of serious brain diseases

Smell is one of the least studied and underestimated senses. It is directly connected to areas of the brain responsible for emotions and memory: signals from olfactory receptors immediately enter the olfactory bulb located in the forebrain. This is why smells can evoke strong emotional responses - and just as easily disappear during a cold or age-related changes. However, the loss of ability to smell may not just be a temporary inconvenience. Scientists are increasingly viewing it as one of the earliest signs of neurodegenerative diseases, including Parkinson's and Alzheimer's.

As reported by TUT.AZ, this was published in The Conversation.

Scientists have found that up to 90% of people with Parkinson's disease notice a decrease in smell many years before motor disorders appear. By the time tremors or stiffness manifest, half of the dopamine neurons have already died, and the disease has progressed to an advanced stage.

Loss of smell could become a valuable biomarker that would allow detection of the disease at its earliest stage. But this symptom is too nonspecific - it can be caused by age-related changes, viral infections, stress, or damage to the mucous membrane.

Nevertheless, new research shows: in some patients, the disease may actually start in the olfactory bulb. Brain areas vulnerable to viruses, toxins, or pesticides may be the first to malfunction - and then pathological changes spread to areas responsible for movement.

With Alzheimer's disease, early disorders are often associated with damage to the locus coeruleus of the brain stem. This structure is responsible for wakefulness and emotional reactions and is closely connected to the olfactory system. When this interaction weakens, the ability to perceive smells deteriorates - long before memory lapses appear.

Some Parkinson's patients also experience olfactory hallucinations - phantom smells of smoke, tobacco, wood. At the same time, real strong odors, such as rubber, smoke, or soap, become barely noticeable. Interestingly, they can still normally smell aromas of chocolate or coffee.

A few years ago, a phenomenon that initially seemed incredible became known: a specific "Parkinson's smell," described as woody-musky. It was first detected by Scottish woman Joy Milne - twelve years before her husband's diagnosis. Later, scientists confirmed: the chemical composition of sebum in patients does indeed change.

For doctors, olfactory disorders are an important guide in complex differential diagnosis between Parkinson's disease and other movement disorders. And for researchers - a chance to study one of the most vulnerable areas of the brain.