Neurological causes of taste disorders

The Etiologies and Considerations of Dysgeusia: A Review of Literature

BACKGROUND

Dysgeusia is a prevalent qualitative gustatory impairment that may affect food intake and quality of life. The facial (VII), glossopharyngeal (IX), and vagus (X) nerves are the three cranial nerves responsible for sensing taste. Typically, dysgeusia is considered a general term for all taste disorders. In addition, dysgeusia may be a symptom of underlying systemic conditions such as diabetes mellitus, chronic kidney disease, respiratory infections, and nutritional deficiencies. Various subjective and objective diagnostic approaches are available to aid clinicians, each with its own set of benefits and drawbacks.

HIGHLIGHTS

Taste impairment can lead to a lack of enjoyment while eating, food aversion, and malnutrition, resulting in a decrease in the quality of life and loss of muscle mass. Therefore, the present review aims to address the probable etiologies, diagnostic aids, and management of dysgeusia. A broad search for studies was conducted using PubMed, Web of Science, Scopus, and Google Scholar. In addition, relevant studies found in the references of the selected articles were also studied.

CONCLUSION

Oral health care providers should be aware of the possible etiologies of dysgeusia, diagnostic tools, and treatment options. Accurate diagnosis of the cause of taste dysfunction has a significant impact on the management of taste impairment.

Case Report: Diagnosis of hypogeusia after oral exposure to commercial cleaning agent and considerations for clinical taste testing

Few reports in the literature document acute taste disturbance following exposure to toxic chemicals. We describe the case of a 54-year-old man who presented with primary complaint of tongue numbness and persistent problems with taste 1.5 years following oral exposure to a commercial cleaning agent. A test of olfaction revealed normosmia for age and gender. Lingual tactile two-point discrimination testing showed reduced somatosensation. Taste threshold testing using a 3-drop method demonstrated severe hypogeusia, though the patient was able to discriminate tastants at lower concentrations with a whole mouth swish and spit test. We conclude that clinical evaluation of dysgeusia can be performed using a number of previously published testing methods, however, determining causative factors may be confounded by duration since exposure, lack of knowledge of baseline taste function, and medications. Although many testing options exist, basic taste testing can be performed with minimal expertise or specialized equipment, depending on the patient history and goals of evaluation.

Case Report: Diagnosis of hypogeusia after oral exposure to commercial cleaning agent and considerations for clinical taste testing

Few reports in the literature document acute taste disturbance following exposure to toxic chemicals. We describe the case of a 54-year-old man who presented with primary complaint of tongue numbness and persistent problems with taste 1.5 years following oral exposure to a commercial cleaning agent. A test of olfaction revealed normosmia for age and gender. Lingual tactile two-point discrimination testing showed reduced somatosensation. Taste threshold testing using a 3-drop method demonstrated severe hypogeusia, though the patient was able to discriminate tastants at lower concentrations with a whole mouth swish and spit test. We conclude that clinical evaluation of dysgeusia can be performed using a number of previously published testing methods, however, determining causative factors may be confounded by duration since exposure, lack of knowledge of baseline taste function, and medications. Although many testing options exist, basic taste testing can be performed with minimal expertise or specialized equipment, depending on the patient history and goals of evaluation.

Sour taste increases swallowing and prolongs hemodynamic responses in the cortical swallowing network

Sour stimuli have been shown to upregulate swallowing in patients and in healthy volunteers. However, such changes may be dependent on taste-induced increases in salivary flow. Other mechanisms include genetic taster status (Bartoshuk LM, Duffy VB, Green BG, Hoffman HJ, Ko CW, Lucchina LA, Weiffenbach JM. Physiol Behav 82: 109-114, 2004) and differences between sour and other tastes. We investigated the effects of taste on swallowing frequency and cortical activation in the swallowing network and whether taster status affected responses. Three-milliliter boluses of sour, sour with slow infusion, sweet, water, and water with infusion were compared on swallowing frequency and hemodynamic responses. The sour conditions increased swallowing frequency, whereas sweet and water did not. Changes in cortical oxygenated hemoglobin (hemodynamic responses) measured by functional near-infrared spectroscopy were averaged over 30 trials for each condition per participant in the right and left motor cortex, S1 and supplementary motor area for 30 s following bolus onset. Motion artifact in the hemodynamic response occurred 0-2 s after bolus onset, when the majority of swallows occurred. The peak hemodynamic response 2-7 s after bolus onset did not differ by taste, hemisphere, or cortical location. The mean hemodynamic response 17-22 s after bolus onset was highest in the motor regions of both hemispheres, and greater in the sour and infusion condition than in the water condition. Genetic taster status did not alter changes in swallowing frequency or hemodynamic response. As sour taste significantly increased swallowing and cortical activation equally with and without slow infusion, increases in the cortical swallowing were due to sour taste.

Dysgeusia in a Patient with Guillain-Barré Syndrome Associated with Acute Hepatitis E: A Case Report and Literature Review

Guillain-Barré syndrome (GBS) is usually triggered by viral or bacterial infection. In addition, it was recently reported that infection with hepatitis E virus (HEV) also causes GBS. A 49-year-old man presented with acute-onset paralysis in all extremities and dysgeusia during an episode of acute hepatitis. Serological tests showed the presence of anti-HEV IgM antibodies and HEV-RNA in the serum. As an electrophysiological examination showed acute demyelinating polyradiculoneuropathy, the patient was diagnosed as HEV-associated GBS. Following the initiation of treatment with intravenous immunoglobulin, his paralysis and dysgeusia rapidly improved. This case suggests that HEV-associated GBS may rarely be complicated by dysgeusia.

Preliminary estimation of the prevalence of chemotherapy-induced dysgeusia in Japanese patients with cancer

Background

Although dysgeusia is a common adverse event in chemotherapy patients; it has not been evaluated using objective methods, and its prevalence and frequency have not been quantified.

Methods

Salt-impregnated taste strips were used to objectively assess dysgeusia in patients receiving chemotherapy at Akita University (n = 38) and those off chemotherapy (n = 9). Participant characteristics, and ongoing and previous chemotherapies were evaluated, and their associations with dysgeusia analyzed.

Results

Dysgeusia developed in 38.8% (14/38) of chemotherapy patients, and was most prevalent in patients receiving 5-fluorouracil (5-FU) or its oral analogs (48.1%, 13/27). Particularly, dysgeusia developed in 55.6% (10/18) of patients receiving oral 5-FU analogs; however, prevalence in patients receiving and off chemotherapy was not significantly different. Patients aged ≥70 years also tended to experience dysgeusia (75.0%, 6/8).

Conclusions

Association with dysgeusia may be higher for some chemotherapeutic drugs. Dysgeusia should be routinely assessed in chemotherapy patients with objective methods such as paper strips; interventions for its prevention may be required.

Taste dysfunction in head and neck cancer survivors

PURPOSE/OBJECTIVES

To describe the prevalence of issues with taste function in survivors of head and neck cancer.

DESIGN

Exploratory, cross-sectional.

SETTING

Outpatients from Saint Louis University Cancer Center in Missouri.

SAMPLE

92 adult head and neck cancer survivors, heterogeneous in cancer site, treatment type, and time post-treatment, ranging from three months to more than 28 years after completion of therapy.

METHODS

Taste discrimination was assessed using high, medium, and low concentrations of sweet, salty, sour, and bitter tasting solutions.

MAIN RESEARCH VARIABLES

Taste, percentage of weight change, tumor site and stage, treatment type, and time since completion of therapy.

FINDINGS

Eighty-five of 92 participants had some measurable taste dysfunction. Confusion between bitter and sour and the inability to discriminate among the different concentrations of the sweet solutions were common. Statistically significant weight loss was associated with dysgeusia.

CONCLUSIONS

Taste dysfunction was a persistent problem across all categories of head and neck cancer treatments, sites, and stages. Participants who reported the loss of one or more specific taste modality performed poorly on the taste test. However, participants could not accurately predict which taste was most severely impaired.

IMPLICATIONS FOR NURSING

Taste dysfunction is a long-term treatment-related side effect for head and neck cancer survivors. Assessing for taste changes and dysgeusia are important nursing considerations, as taste loss is distressing and associated with decreased appetite. Future studies are needed to identify interventions to help patients better manage and adapt to this long-term complication of cancer therapy.

KNOWLEDGE TRANSLATION

Flavors are recognized by taste, texture, aroma, thermal quality, and visual cues. A disruption of one or more of those sensory experiences alters flavor recognition. Having intact taste sense but impaired flavor recognition is possible. Finally, taste is not accurately self-reported because it is commonly confused with flavor recognition.

[Bilateral ageusia caused by right thalamic infarction]

A 58-year-old man noticed left hemiparesis at 01:00 pm on a particular day in March 2006. Because his symptoms developed gradually, he was referred to the emergency room of our hospital at 05:00 pm and was admitted with the diagnosis of cerebral infarction. While he presented slight left hemiparesis involving the face, impairment of sensation was not apparent. Diffusion-weighted magnetic resonance imaging of the head showed a high-intensity area in the ventromedial area in the right thalamus. The patient was treated with anticoagulant and edaravone, and his symptoms resolved on hospital day 3. When he began eating, he noticed that he was unable to distinguish tastes. On day 5, we performed taste examination using a commercial kit. The taste sensation on both sides of his tongue was severely affected, while the touch sensations in the mouth and olfaction were preserved. His symptoms improved spontaneously and resolved on hospital day 15. This is the second case report of bilateral ageusia caused by right thalamic infarction. Our study indicates the importance of the right thalamus in taste sensation involving both sides of the tongue.

Smell and taste disorders

Smell and taste disorders can markedly affect the quality of life. In recent years we have become much better in the assessment of the ability to smell and taste. In addition, information is now available to say something about the prognosis of individual patients. With regard to therapy there also seems to be low but steady progress. Of special importance for the treatment is the ability of the olfactory epithelium to regenerate.