Researchers know that alcohol abuse can lead to Korsakoff’s syndrome, a severe mental disorder characterized by memory loss and disorientation. Studies dating back to the end of the 1970s have shown that Korsakoff’s syndrome, in turn, is associated with olfactory deficits, specifically, dysfunctions in odor identification, discrimination, memory, sensitivity, and intensity. A study in the March issue of Alcoholism: Clinical & Experimental Research has found that "uncomplicated" alcoholics, those without amnesia or dementia, also have impaired olfactory functioning.
"Research suggests that olfactory deficits in Korsakoff’s syndrome are associated with neuropathological changes in brain regions, particularly the mediodorsal thalamus and prefrontal brain areas," said Claudia I. Rupp, clinical neuropsychologist and assistant professor at the University Clinics of Innsbruck, and first author of the study. "While the majority of treated patients with chronic alcoholism do not meet the criteria for ‘alcohol organic mental disorders’ such as Korsakoff's syndrome or alcohol-induced dementia, many show mild to moderate impairments in neuropsychologic functioning, as well as a variety of neuropathological and morphological changes. Despite interest in olfactory deficiencies in individuals with Korsakoff's syndrome or dementia, there has been little systematic research of olfactory functions in nonamnesic and nondemented patients with chronic alcoholism."
Rupp and her colleagues examined two groups that were matched for age, gender and smoking status: 30 alcohol-dependent patients (16 males, 14 females) and 30 healthy controls (16 males, 14 females). Olfactory performance was assessed unirhinally (one nostril at a time) using "Sniffin’ Sticks," pen-like odor-dispensing devices. Results were divided into three domains: odor threshold (sensitivity), meaning the lowest concentration of an odor where a faint presence is reliably detected; discrimination, the ability to qualitatively distinguish among smells; and identification, the ability to recognize an odor’s name with the help of response cues. The results were also added together for a composite TDI (Threshold, Discrimination, Identification) score.
"Our findings demonstrate that olfactory impairments exist even in nonamnesic and nondemented patients with alcohol dependence," said Rupp. "A large number of patients, 57 percent, had hyposmia, a diminished sense of smell. Impairments in odor sensitivity, discrimination and identification abilities were not related to age, gender, or duration of abstinence from alcohol; nor were they attributable to smoking habits or general cognitive abilities. Rather, the deficits appear to be alcohol related. In summary, our findings demonstrate that alcoholism is associated with olfactory impairments, and that these deficits – at least odor discrimination and identification – likely reflect dysfunction in central neural circuitry of olfaction."
"Uncomplicated alcoholics constitute between two percent, for women, and five percent, for men, of the population of industrialized countries," noted Karl Mann, full professor in the department for addictive behavior and addiction medicine at the University of Heidelberg. "It seems that a large proportion of [this group] is compromised by olfactory dysfunction. Without the full potential to smell, [these individuals] also lack some of their capabilities to taste, one of the main sources of pleasure in our daily lives. This certainly constitutes a deficit in ‘quality of life’ for these patients."
Rupp concurred. "It is not very well known that taste only contributes basic sensations such as sweet, sour, salty and bitter," she said. "The most important sensory component during eating and drinking is olfaction, which mediates acceptance and pleasure of food, and is a prerequisite for the pleasant feelings accompanying an enjoyable dinner. On a more practical level," she added, "an intact sense of smell can serve as a warning device, notifying us of dangers such as toxic leaking gas, poisonous fumes, the presence of fire, or spoiled food."
In addition to categorical deficits in odor sensitivity, discrimination and identification, researchers found lower composite or TDI scores that were, in turn, associated with longer periods of regular alcohol intake, as well as higher values of gamma-glutamyl-transferase (GGT), an enzyme that indicates liver injury.
"Since the composite score is the sum of results obtained from threshold, discrimination and identification measures," said Rupp, "it may be regarded as overall olfactory functioning. The score allows classification of an individual’s absolute olfactory abilities, for instance, as normosmia, normal absolute olfactory abilities, or hyposmia, decreased absolute olfactory abilities. The findings that TDI scores were correlated with GGT values, as well as longer periods of regular alcohol intake, also strongly indicate that olfactory dysfunctions are alcohol-related impairments. The association between alcohol and liver injury has been well known for a long time." Recently, added Rupp, research has found that patients with cirrhosis of the liver also have olfactory impairments.
Mann suggested that the next step for researchers would be to correlate olfactory dysfunction with brain imaging, such as magnetic resonance imaging (MRI) scans. "It would be of interest to look at an association of olfactory dysfunction with brain atrophy in certain areas of the central nervous system such as the thalamus," he said.
"Apart from the neuroanatomical overlap between alcohol-related neuropathological changes and the olfactory system," added Rupp, "our findings may also have an impact on alcohol research using olfactory stimuli in the investigation of craving. Patients with chronic alcoholism are also very well known to have bad nutrition habits. Impaired olfactory functioning may play a role in both of these areas."
Funding for this Addiction Science Made Easy project is provided by the Addiction Technology Transfer Center National Office, under the cooperative agreement from the Center for Substance Abuse Treatment of SAMHSA.
Articles were written based on the following published research:
Rupp, C.I., Kurz, M., Kemmler,G., Mair, D., Hausmann, A., Hinterhuber, H., Fleischhacker, W. W. (March 2003). Reduced olfactory sensitivity, discrimination, and identification in patients with alcohol dependence. Alcoholism: Clinical & Experimental Research, 27(3), 432-440.