Hyperosmia

Hyperosmia (heightened smell function) is a relatively rare condition, usually of idiopathic origin, in which quantitative olfactory testing reveals heightened performance (e.g., UPSIT scores of 40 and detection threshold values that are several orders of magnitude below those of normal subjects). Although untreated adrenal cortical insufficiency is reportedly accompanied by hyperosmia, y this work has not been replicated, and animal studies have showed no evidence of heightened odor detection performance following adrenalectomy. y Indeed, adrenalectomy reduces rather than enhances peripheral nerve responses to a number of types of sensory stimuli, including tastants. y There have been suggestions of hyperosmia in patients with syndromes such as multiple chemical sensitivity, but the limited data available fail to support this notion. y Hyperosmia occurs in some patients with epilepsy during the interictal period, although, as noted earlier, patients with long-term epilepsy

and intractable seizure activity, such as candidates for temporal lobe resection, typically are hyposmic. Dissociated Olfactory Function Syndromes

Some types of olfactory tests (e.g., tests of odor identification and discrimination) may be altered by central brain lesions that have little or no influence on other types of olfactory tests (e.g., odor detection thresholds). Thus, a dissociation between elements of the olfactory perceptual process may occur. For example, H.M., the only patient on record to have undergone bilateral temporal lobe resection, is said to perform normally on tests of odor detection, suprathreshold intensity discrimination, and adaptation, but abnormally on tests of odor quality discrimination and identification. y In one study, resection of left temporal lobes, right or left frontal lobes, and the right frontotemporal region significantly depressed scores on the UPSIT but not on a detection threshold test. y As noted earlier, however, care must be taken in the interpretation of such test results, given the fact that many olfactory tests, most notably some olfactory threshold tests, are relatively unreliable and thus insensitive to subtle alterations in smell function.

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