June 2019

Modes of Smell Recovery after Successful Treatment

There are two major modes of smell recovery after successful treatment. They occur in tandem but one precedes the other.

The first mode of smell recovery involves an increase in olfactory receptor number with an increase in olfactory detection. This mode results in the patient being able to detect odors not previously appreciated. The patient can detect an odor but may not be able to recognize the odor character. The patient knows that an odor is present but cannot define what the odor is. The improvement in smell function is the earliest sign of smell improvement after intranasal theophylline. This improvement may occur after 2-6 weeks of treatment and is the earliest sign of smell return.

The second mode of smell recovery after successful treatment involves the ability to recognize odor character. This almost always follows improved receptor function. With the onset of smell loss the diminution or absence of receptor stimulation causes the brain “to go to sleep” since the usual inputs into the olfactory recognition, integration and memory brain sites is decreased or missing. These receptor-integration sites become functionally impaired but with the re-initiation of olfactory stimuli with projections to these sites, the brain “wakes up” and begins to process these incoming signals and odor recognition returns. Over time more and more of these recognition sites become more active and the patient begins to recognize more odors and the treatment process is considered successful — the patient feels he/she is beginning to smell again.

If only the first mode of successful therapy occurs, the patient may not experience what he/she considers successful smell return.

It is usually only when smell recognition occurs that the patient appreciates what he/she considers smell and recognizes the benefit of successful therapy to restore smell function to what it was prior to onset of smell loss.