Smell Test

Olfaction is the sense that allows us to perceive odors. It is either directly through a nasal inspiration, or by retro-olfaction during oral inspiration, causing a rise in odor molecules to the olfactory cleft. It is important to know that our brain detects odors through receptors located in the nose and throat.

The loss of smell is usually caused by damage to these receptors. The causes are variable: nasal polyposis, nasal surgery, head trauma, diabetes, smoking, sinusitis, medication and brain tumor.

The loss or reduction of smell may also be a symptom of a neurodegenerative disease. Indeed, these diseases (Alzheimer’s disease, Huntington’s, Parkinson…) cause damage to nerves playing a major role in the functioning of smell and taste.

There are different methods to test the smell: there are objective tests (very long, especially in research) and subjective psychophysical tests (quick and easy, but require good cooperation with patients).

The psychophysical test includes 4 stages from screening to discrimination of odors:

• Screening: Screening using a small amount of high concentration odors.
• Threshold: Odors presented around the perception threshold. The test reflects peripheral olfactory function. The advantage of this test is the reveal of minor disorders.
• Identification: Presentation of a large amount of high concentration odors which must be recognized among multiple choices.
• Discrimination: Presentation of high concentration odors. The patient must recognize an odor that is different from other ones.