Taste and Smell Disorders Caused by Cancer Treatments Add to Patients’ Problems

taste and smell disorderAlthough the mechanisms underlying abnormalities in the senses of taste and smell in cancer patients are unknown, such disturbances clearly decrease quality of life for the majority of cancer patients—and clinicians need to be aware of the problem in order to help a person’s recovery.

This is the word from a study recently published in The Journal of Supportive Oncology (2009;7:58-65). Jae Hee Hong, PhD, Pinar Omur-Ozbek, PhD, Brian T. Stanek, and coinvestigators from Wake Forest University Comprehensive Cancer Center and Virginia Tech’s food science and technology department and biomedical engineering school conclude, “Oncologists who understand the types and causes of taste and olfactory abnormalities may be better prepared to discuss and empathize with these negative side effects.”

Altered sensory perception can undermine a person’s struggle against cancer by causing malnutrition and anxiety. One study cited by Dr Hong and colleagues found that malnutrition, not malignancy, was the primary cause of morbidity in 20% of cancer patients.

Dr Hong and colleagues explain that disorders of taste and odor can result from cancer itself or from cancer treatments, with 68% of chemotherapy patients reporting such problems. But the specific causes of these alterations often remain unidentified.

How Senses Go Bad
According to the researchers, problems with taste and smell break down into 3 categories: loss of sensitivity, distorted perception, and hallucination. The abnormalities may take the following forms:

• absence of taste perception (ageusia) or odor perception (anosmia)
• reduced sensitivity to taste perception (hypogeusia) or odor perception (hyposmia)
• distortion of taste perception (dysgeusia) or odor perception, with the person being unable to identify odors (dysosmia); in dysosmia, the person may think he or she smells something when no odor is present (phantosmia), be unable to tell the difference between perceived odors (agnosia), or have altered odor perception when 1 scent is present with another (parosmia)
• perception of taste even when no substance has been ingested (phantogeusia); although the perceived taste is often described as metallic or salty, some patients have described it as bitter, sweet, sour, peppery, greasy, soapy, powdery, or chemical.

Taste Complaints Common in Patients with Head-and-Neck Cancer
Changes in taste acuity—ageusia and hypogeusia— depend on the site of the tumor, but people with head and neck cancer report more problems than do people with breast cancer or lung cancer. According to studies cited by Dr Hong’s group, approximately 85% of patients undergoing radiation treatment of the head and neck experienced unpleasant taste changes.

“Irradiation of the taste buds frequently leads to partial or complete loss of taste or alteration of taste,” affirms Michele Y. Halyard, MD, in a commentary accompanying the Hong study. An associate professor of radiation oncology at the Mayo Clinic in Scottsdale, Ariz, Dr Halyard adds that taste recovery may take 6 to 12 months after head-and-neck radiotherapy.

Zinc and other heavy metals play a part in the physiology of taste function, and uncontrolled studies have shown zinc supplementation to improve taste abnormalities in people with head-and-neck cancer who were treated with external-beam radiation therapy. Dr Halyard and colleagues conducted a large randomized trial in which zinc did not help prevent or recover taste loss caused by radiation therapy, but, conflictingly, a small pilot trial demonstrated more promising results. Zinc’s specific role in taste perception is unknown, writes Dr Halyard, “but it is a recognized cofactor of alkaline phosphatase, which is the most abundant enzyme within the taste-bud membrane.”

Dr Halyard recommends that clinicians consider arranging a formal nutritional consultation for patients undergoing cancer treatment and initiating enteral feeding if necessary. “Nutritional intervention has been shown to improve not only quality of life in cancer patients but survival as well and should play an important role in the management of patients with alterations in taste and smell that impact oral intake,” she contends.

Odor Identification and Aversion
Sense of smell doesn’t appear to be as affected as sense of taste in cancer patients, note Dr Hong and colleagues. People with lung, ovarian, and breast cancers did not differ significantly from people without cancer in 1 test measuring smell sensitivity. In addition, radiotherapy administered to patients with oropharyngeal cancer did not significantly change their ability to recognize odors.

Nevertheless, chemotherapy and radiation have been found to be major causes of dysosmia. In 1 study of 40 individuals with breast cancer, most recovered their ability to identify odors and had increased smell acuity 6 to 9 months after radiotherapy treatment.

Abnormal taste and odor perception are building blocks to food aversion. Many cancer patients report that high-protein foods give off an unpleasant taste and odor. Red meat seems to be a particular culprit; patients appear better able to tolerate protein in the forms of fish, chicken, eggs, and cheese. High-fat foods, vegetables, chocolate, and caffeinated drinks also frequently make the food-aversion lists of people with cancer.

Another contributor to taste aversion is xerostomia, otherwise known as “dry mouth.” This condition occurs in cancer patients when radiation damage to the salivary glands diminishes saliva secretion. Xerostomia is strongly linked with taste alteration, particularly with the problem of metallic tastes or aftertastes.

Better Understanding Will Lead to Better Management
Dr Hong et al conclude that new management strategies are needed to help cancer patients resolve taste and odor malfunctions. In a separate statement announcing the study, coinvestigator Andrea Dietrich, professor of civil and environmental engineering at Virginia Tech and an expert on the taste and odor assessment of water among cancer patients, pointed out that one of the purposes of the study was to provide both researchers and clinicians with a better understanding of the types and causes of taste and odor dysfunctions so that they can develop treatments for these conditions and improve quality of life for their patients.

(Source: Oncology Nursing News)