Dysgeusia is an alteration in taste and is associated with ageusia, which is the complete lack of taste, and hypogeusia, which is the decrease in taste sensitivity. Dysgeusia is a common complaint of patients undergoing chemotherapy and research indicates that 46-77% of patients receiving chemotherapy report changes in taste (Bernhardson, Tishelman, & Rutqvist, 2008). These changes include sweet, sour, salt or bitter taste changes, decreased taste sensations, and metallic tastes (Bernhardson, Tishelman, & Rutqvist, 2007). Chemotherapeutic agents such as cyclophosphamide, dacarbazine, doxorubicin, 5-FU, methotrexate, nitrogen mustard, cisplatin, and vincristine have frequently been associated with taste alterations (Camp-Sorrell, 2005). While patients on these chemotherapies report dysgeusia, all patients on chemotherapy are at risk for taste alterations due to complications of treatment.
Stomatitis and mucositis, oral thrush, zinc deficiency, and antibiotic use have been linked to changes in taste (Strasser et al., 2008; Cunningham, 2004). Taste alterations, whether caused by chemotherapy or a side effect of the chemotherapy, leads to food aversion. In fact, over 50% of patients develop a food aversion after chemotherapy and decreased oral intake leads to involuntary weight loss and ultimately malnutrition (Berteretche et al., 2004; Strasser et al., 2008). The consequences of malnutrition are deleterious. Prolonged morbidity and chemotherapy-induced side effects, decreased response to therapy, and cancer treatment delays can result from nutritional compromise (Halyard et al., 2007).
In addition to the obvious physical consequences of dysgeusia, quality of life (QOL) is drastically impaired for the cancer patient. Eating is a social event and patients no longer derive enjoyment from the experience because of taste alteration. Patients report avoiding eating around friends and family and isolate themselves during profound episodes of dysgeusia (Bernhardson, Tishelman, & Rutqvist, 2007). Dysgeusia is viewed as extremely frustrating and patients rank taste change second only to alopecia as a bothersome side effect of chemotherapy (Bernhardson, Tishelman, & Rutqvist, 2007). While most patients are extremely irritated by this side effect of chemotherapy, this symptom is rarely addressed by the healthcare provider. In fact, only 17% of patients receive information about dysgeusia before initiating chemotherapy (Rehwaldt, 2009). Dysgeusia has a negative impact on QOL and clinical outcome for patients undergoing chemotherapy so it is vital that healthcare providers inquire about taste alteration as to allay some of the potential consequences.
Several theories exist regarding the pathophysiology of dysgeusia, but no one etiology has been elucidated. Direct insult to the taste cell receptors is one suggested theory. Some chemotherapy agents are secreted in saliva and gain direct contact with taste receptors. Patients may experience a metallic or "chemical" taste when chemotherapy is delivered, and this is consistent with drug secretion in saliva (Epstein & Barasch, 2010). Hong et al. (2009) suggest that cell damage occurs in three ways: (1) a decrease in the number of normal cell receptors, (2) alteration of cell structure or receptor surface changes, and (3) interruption of neural coding. The turnover rate of normal human taste bud cells is 10 days and chemotherapy kills cells with high turnover rates resulting in taste alteration. While most taste alterations are transient lasting less than three months after completion of treatment, dysgeusia may persist after drug clearance due to damage to the taste buds (Steinbach et al, 2009).
Neurotoxicity from systemic chemotherapy is another probable cause of dysgeusia. Cranial nerves VII (facial), IX (glossopharyngeal), and X (vagus) control integral sensory functions in the tongue and damage to them has been implicated in taste alterations (Epstein & Barasch, 2010). Xerostomia or dry mouth has also been implicated in the development of dysgeusia (Perry, 2008). Decreased saliva secretion alters the amount of chemicals released by the foods thereby changing the taste. The five tastes, sweet, sour, bitter, salty, and umami (savoriness), can all be affected. Most commonly the bitter taste threshold is lowered, while the sweet threshold is increased (Camp-Sorrell, 2005). Steinbach et al. (2009) reported salty taste to be altered most often. While xerostomia is more commonly seen in head and neck cancer patients receiving radiation therapy, it is an important symptom to address in all patients receiving chemotherapy.
Chemotherapies such as cyclophosphamide, epirubicin/methotrexate, and 5-fluorouracil when used in the adjuvant setting have been implicated in causing xerostomia and a 49.9% prevalence rate of xerostomia has been observed in patients undergoing chemotherapy (Jensen et al., 2010). Since no one mechanism has been clearly identified in development of dysgeusia, the establishment of effective treatment of this symptom has been delayed.
Dysgeusia is generally a subjective patient complaint and rarely are exam findings necessary to make a diagnosis. Unfortunately, most patients with chemosensory ailments, such as dysgeusia, are left unmentioned unless the healthcare provider specifically asks about them (Bernhardson, Tishelman, & Rutqvist, 2007). Dysgeusia may not yield physical findings, but several related medical problems may be present. These include depressed mood, oral problems, nausea, and appetite loss (Bernhardson, Tishelman, & Rutqvist, 2007). The patterns and intensity of dysgeusia vary considerably. Some patients prefer sweet foods, while others are able to tolerate more salty foods. Steinbach et al. (2007) found most food aversion was to meat, followed by chocolate, fruit, and coffee. Taste sensations are also varied and some patients report chemosensory changes as "saw dust," "toilet paper," and "metal" (Bernhardson, Tishelman, & Rutqvist, 2007).
Specific risk factors may increase the risk of developing dysgeusia. Poor oral hygiene, infection of the oral cavity, and dentures have been associated with chemotherapy-induced taste alterations (Camp-Sorrell, 2005). Bernhardson, Tishelman, and Rutqvist (2007) found taste changes more prevalent among women and younger patients, while smoking was not found to be a risk factor. The type of chemotherapy is another risk factor for the development of dysgeusia. Steinbach et al. (2007) found taxane-based chemotherapies to cause the most severe taste alterations, while Wickham et al., (2008) reported cisplatin and doxorubicin to be the agents most likely to cause dysgeusia.
Many differential diagnoses are associated with clinical presentation of dysgeusia. Taste alteration may be the result of mucositis, nausea, xerostomia, oral infections, zinc deficiency, or depression (Strasser et al., 2008; Cunningham, 2004). Dysfunction of the olfactory sense could also lead to taste changes and diagnoses such as sinusitis and nasal polyps should be considered. Medications such as anti-depressants, antihypertensives, and antiemetics may be responsible for taste changes and use of such medications needs to be assessed during clinical evaluation (Comeau, Epstein, & Migas, 2001).
The treatment of dysgeusia has vexed clinicians for decades. This is partially due to incomplete understanding of its pathophysiology, but also because this diagnosis has been understudied. Currently, no guidelines exist for the pharmacologic management of dysgeusia. Several studies have looked at the use of zinc sulfate in mitigating taste alterations, but conflicting findings have resulted. Two pilot studies found that zinc supplementation increased recovery in taste acuity, but a larger phase III trial found that zinc supplementation had no affect on taste alteration (Ripamonti, et al., 1998; Yamagata, et al., 2003; Halyard et al., 2007). This treatment should be used with caution until further research confirms its efficacy because excessive zinc supplementation can negatively impact the immune system (Peregrin, 2006).
The amino acid glutamine has also been investigated as a treatment for dysgeusia. Strasser et al. (2008) investigated glutamine’s role in reducing taste alterations because research supports the use of glutamine in improving mucositis and recovery time in patients receiving high-dose chemotherapy (Savarese et al., 2003; Garcia-de-Lorenzo et al., 2003). Unfortunately, glutamine has not shown to reduce taste alteration in patients receiving taxane-based chemotherapies (Strasser et al., 2008). More research needs to occur before pharmacologic recommendations can be made.
Non-pharmacologic management strategies and patient education have been the mainstay of treatment for dysgeusia. Many of the suggested recommendations deal with food preparation. Several published studies (Hong et al., 2009; Rehwaldt et al., 2009) along with The American Institute for Cancer Research (2010) suggests the following for improving the flavor of foods:
In addition to modifying food preparation techniques, cognizant oral mouth care practices can alleviate some taste alterations. Frequent oral hygiene such as regularly rinsing the mouth and brushing the teeth are good suggestions. Routine dental visits are also helpful and may help in identifying any new infections.
Bernhardson, Tishelman, and Rutqvist (2007) suggest psychological strategies for dealing with chemosensory changes such as dysgeusia. Patients in this study stated giving up expectations of food and drink and using taste memory helped them with taste changes. Remembering how things tasted and using these memories in meal situations was found to be helpful when dysgeusia occurred. Having someone else prepare the meal was also found to be effective at reducing food aversion.
In general, there is no cure for chemotherapy-induced dysgeusia, only strategies to help manage the disorder. Taste alteration varies with each patient and specific suggestions for dysgeusia management must be tailored on an individual basis. Modification of food preparation appears to be only the effective management approach at this time.
Dysgeusia is a condition that not only affects the QOL of patients undergoing chemotherapy, but has the potential to prolong morbidity and decrease response to therapy. Since taste alteration is rarely brought up by the healthcare provider, a conversation about dysgeusia needs to take place before the initiation of chemotherapy. The patient can therefore prepare for the psychological and physical manifestations of taste alteration. Stress of the patient may be further alleviated to know that dysgeusia is a transient condition lasting approximately 3 months after completion of chemotherapy (Steinbach et al, 2009; Bernhardson, Tishelman, & Rutqvist, 2007). No pharmacologic agents have been shown to decrease dysgeusia and no evidence-based guidelines have been developed for its management. Currently, only food preparation techniques have been proven helpful in ameliorating taste alterations (Rehwaldt et al., 2009; Hong et al., 2009). Further research of this understudied disorder is necessary to understand the etiology of dysgeusia and therefore assist in the development of new management strategies.
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