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The Taste and Smell Clinic

July 2019

Improving Smell Function in Head Injury Patients with Intranasal Theophylline

At least 60% of patients who have had traumatic brain injuries (TBI) develop smell loss (hyposmia). Most patients are completely surprised at this since they had no knowledge that this might occur. They generally noted this loss after their head injury when they recognized that food had little or no flavor and that food odors were not present.

Most patients complained to their physician who usually told them that their smell function would return over time. When this did not occur patients were told that they had severed their olfactory nerves and that they would never smell again. This observation is totally incorrect in that olfactory bulbs are usually present in these patients, although somewhat smaller in volume than in normal people. With this anatomical observation of normality, what is the problem?

Following a TBI there are biochemical changes that occur in which specific growth factors that maintain olfactory stem cells are inhibited—they are decreased in their secretion due to the TBI. These decreases in growth factors cause the stem cells which maintain the olfactory receptor cells to lose their ability to function normally and with this inhibition of function they lose their ability to stimulate the olfactory receptor cells. This inhibition causes the receptor cells to lose function, to disappear. With the loss of receptor input the olfactory system shuts down and patients lose the ability to smell.

Treatment with intranasal theophylline stimulates these stem cells to initiate growth in olfactory receptors such that smell function returns with the ability to recognize odors once the brain regains function.

In our current studies over 90% of patients after TBI treated with intranasal theophylline report some ability to detect odors although this improvement maybe limited. Indeed patients progress from total loss of smell to some ability to detect odors at high concentration. They also report an improvement in their ability to taste tastants such as, salt, sweet, sour and bitter and began to obtain flavor from many foods.