Olfactory Dysfunction

Gustatory function consists of fine taste (eg, distinguishing turkey from chicken), which is an olfactory function, and crude (lingual) taste (eg, distinguishing sweet from sour), which is mediated through the taste buds. The sense of smell and fine taste starts to diminish gradually when persons are in their 50s, because of neural degeneration. However, years of cigarette smoking may accelerate the process. Loss of fine taste does not appear to be related to loss of lingual taste or deficits in cognition. In the elderly, the incidence of a diminished sense of smell (hyposmia) is about 40%.

Abrupt changes in olfactory function can result from influenza or viral infections that affect the olfactory receptors in the superior region of the nose. These changes are often permanent (except when caused by a common cold virus); zinc tablets are a suggested but unproven remedy. Abrupt changes in olfactory function may also result from head trauma, particularly if the cribriform plate is fractured, and from brain tumors in the region of the cribriform plate. A CT scan of the sinuses with coronal views through the cribriform plate can help rule out fractures and tumors.

In the elderly, loss of smell and fine taste may contribute to a lack of interest in eating and maintaining a proper diet and may lead to the harmful, excessive use of salt and sugar to overcome loss of subtle flavors. More hazardous, some patients lose the ability to smell ethyl mercaptan, the malodorous additive to natural gas that makes gas leaks apparent. A few patients report an unpleasant taste in the mouth (dysgeusia) or an unpleasant smell (dysosmia).