ANOSMIA   [ back to Glossary Index ]
Anosmia is the partial or total loss of the sense of smell. A blow to the head can cause anosmia by mechanical shear injury to the bulbs of the olfactory nerve which lie sandwiched between the bottom of the frontal lobes and the cribiform plate of the skull, a vulnerable anatomic arrangement described as "two wet match sticks on a cheese grater." A blow to the head can also cause anosmia by damage to smell processing cells in the orbito-frontal or anterior temporal lobes or by mechanical damage to nasal structures. The ability to perceive food flavor results from the integration of smell and taste in the brain, probably in the orbito-frontal cortex or in the insula. When the sense of smell is lost or diminished, the ability to perceive food flavor is also lost or diminished. Since the ability to taste and enjoy one's food and drink is largely dependent on the sense of smell, anosmia typically leads to reduced appetite and weight loss. In some patients it leads to weight gain, because they must eat highly salted, deep fried foods to gain any sense of food flavor. Approximately 30% of patients with anosmia know they have lost their sense of smell  and taste before being tested by the doctor. These people are understandably saddened by this deprivation of enjoying food. While some patients become anorexic due to complete disinterest in food, others become obese because very salty, deep fried foods are the only ones with any appeal to them.  The most comprehensive , accurate test for anosmia is the 40 item, forced choice University of Pennsylvania Smell Identification Test.

Although in the great majority of cases the sense of smell is lost forever, and cannot be restored, there are very good reasons to test for it. This is because there is a high correlation between having anosmia and having orbito-frontal brain injury, the form of brain injury which is associated with dysexecutive syndrome (inability to complete planned activity),  emotional lability

(disruptive mood swings), impulsive behavior and failure to adapt behavior to the lessons of experience. These psycho-social sequelae of a TBI can prevent successful return to work or successful community re-integration. Hence anosmia is not only a problem in itself, but a potential clue as to why a person with TBI is not meeting expectations for recovery.