What is the relationship between loss of smell and Parkinson's disease

In 1997, the World Health Organization declared April 11 as World Parkinson's Day, celebrating the birth of James Parkinson, a British neurologist, who in 1817 published a book where, for the first time, the disease was described as “agitant paralysis”. Since then, events and activities have been held all over the world with the aim of raising awareness and reflection about this disease.

Parkinson's is defined as a process of neuronal degeneration that affects movements. Those who have it have altered neurons in a brain area called substantia nigra and a decrease in the amount of dopamine, which is a neurotransmitter that sends signals to coordinate movements in the body.

It has a worldwide prevalence of around 0.3 per cent in the general population. In people over 60 years of age, this figure reaches 1% (that is, one in 100 people may have symptoms) and is more common in men than in women. In rare cases, the disease can affect people under the age of 40.

Although we do not have local statistics in our country, it is known that up to 10% of the population between 60 and 65 years old could have the disease, and some cases of juvenile Parkinson's have also been described. It is necessary to warn about this pathology and, above all, about premotor symptoms, which appear much earlier than the most obvious manifestations of the disease.

The premotor symptoms are:

- Loss of smell (in general, hyposmia).

- REM sleep disorders: it is the stage of deep sleep, the dreamlike stage, in which vivid dreams and movements appear during sleep (spontaneous kicks, falls and even punches).

- Constipation: neuronal alteration also affects the intestine and the evacuation rhythm.

- Depression: signs of apathy or disinterest, anxiety or changes in behavior may appear.

With regard to the alteration of smell, it is a quantitative disorder, that is, it is a decrease in the ability to smell known as hyposmia. This symptom can precede up to 20 years the appearance of motor manifestations.

In recent years, and even more so in the context of the COVID-19 pandemic, interest in smell, the unjustly relegated and forgotten sense has increased. Smell has several functions. One of the most important is that of alarm: it allows us, for example, to warn the presence of gas or smoke and, in this way, avoid accidents.

Smelling food makes us delight (keep in mind that smell gives 80% of the taste), but it also helps us detect spoiled foods and, thus, avoid poisoning. This sense is indispensable for maintaining personal and home hygiene, and plays a very important role in interpersonal relationships.

Once the most common causes of hyposmia have been ruled out, such as rhinitis, chronic rhinosinusitis, allergic diseases and occupational disorders (e.g., sommeliers and tasters), it is important to think of hyposmia as one of the earliest symptoms of Parkinson's, to begin studies and early treatment to improve the quality of life.

Dr. Stella Maris Cuevas MN: 81701. Otolaryngologist - Expert in smell - Allergist Former President of the Otolaryngology Association of the City of Buenos Aires (AOCBA)

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