Major Research Findings

Olfactory training (OT) is a well-established treatment for individuals with olfactory dysfunction. However, the effect on individuals with normosmia remains uncertain. 6 explored how OT with different exposure lengths affect olfactory function in individuals with normosmia.

Platinum-based chemotherapy is known to cause taste and smell changes (TSCs) via a host of mechanisms. This study documented the first instance of an individual regaining their sense of olfactory detection following treatment with oxaliplatin for colorectal adenocarcinoma. 10 theorized that the improvement in smell may have resulted from oxaliplatin-induced destruction of nasal polyps. They suggest that platinum-based chemotherapy may be a therapeutic benefit for patients with anosmia secondary to nasal polyposis.

Taste and smell disorders (TSDs) are common side effects in patients undergoing cancer treatments. 1 looked at the oncological treatments that cause taste and smell alterations and their time of onset. This review identified the cancer treatments that mainly lead to taste and smell changes and provides evidence for wider studies, including those focusing on prevention.

The sense of smell greatly affects our lives and is closely related to overall quality of life and health. 11 highlights the importance of olfaction and how its loss can be a key symptom of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Olfactory training is an effective treatment for olfactory dysfunction.

Dysgeusia, or taste disorder, is a common complication of COVID-19 caused by SARS-CoV-2 infection. 15 reviews the physiological process of taste perception, the potential mechanisms of taste disorders related to SARS-CoV-2 infection, and strategies for prevention and treatment.

This study aimed to determine the prevalence, severity, course, and long-term findings of smell and taste disorders of COVID-19 patients in mild-moderate and severe-critical disease spectrum. 21

This study evaluated and compared the outcomes of a sensory wellbeing workshop in online versus face-to-face formats among a sample of patients with eating disorders (ED). 13

This study demonstrated that innovative quantitative electroencephalography (QEEG) can be used to assess cognitive function disorders reported after the COVID-19 pandemic. 7 found significantly higher values of all measurements of alpha, theta, and beta2 waves in the study group.

This pilot study evaluated the effectiveness of intranasal and intraoral photobiomodulation (PBM) administrations in the management of anosmia and ageusia. 16 showed a significant functionality improvement of both olfactory and gustatory functionality.

This study evaluated the prevalence of smell dysfunction, along with its risk factors, in COVID-19 patients. 8 also explored the relation to other factors such as disease severity, history of COVID-19 vaccinations, and medical treatment for COVID-19 infection.

Olfactory dysfunction can lead to profound reduction in quality of life and may arise from many different causes. 22 discusses the etiology, diagnosis, and treatment of olfactory dysfunction.

This double-blind randomized clinical trial evaluated Photobiomodulation (PBM), Transmucosal Laser Irradiation of Blood (TLIB), and B complex supplementation as alternatives to treat COVID-19 Related Long-Term Taste Impairment (CRLTTI). 5 found that PBM, TLIB, and B complex might be treatment options in the management of CRLTTI, but lack total remission of taste and smell perception.

Olfactory and gustatory dysfunctions (OGDs) are key symptoms of COVID-19. 2 highlights the need for effective treatment and early strategies to prevent these dysfunctions.

The CLINMIR Protocol evaluated the regular consumption of a food supplement containing a miraculin-based novel food, dried miracle berry (DMB), on the taste perception and nutritional status of malnourished cancer patients. 3 aims to improve food taste perception and nutritional status in patients with taste distortion.

This trial aimed to monitor the outcomes of persistent post-COVID-19 smell and taste disorders after cerebrolysin therapy, a NTF, and olfactory and gustatory trainings. 4

This study explored physicians' current practice, opinions, knowledge, and likelihood of recommending placebos in future pediatric care. 14

This review summarizes common reversible causes of olfactory and/or gustatory dysfunction and current treatment modalities. 17 suggests that treatment may include olfactory training, topically applied steroids and perhaps surgery.

This narrative review summarizes current knowledge on possible effects of intranasal insulin on the sense of smell. 12 suggests intranasal insulin administration as a potential treatment, influencing the regenerative capacities of the olfactory mucosa.

This study investigated whether the efficacy of OT could be modulated with multisensory integration, attention towards odors, odor complexity, or physical activity. 9 found that both multisensory interaction and attention towards odors plus OT appeared to facilitate improvement of olfactory function in healthy individuals.

This study explores therapeutic and restorative modalities for olfactory and gustatory dysfunction (OGD) disorders. 20 discusses the lack of specific medication or treatment of any noteworthy efficacy for OGD.

Previous studies demonstrated the difficulty of patients with Head and Neck Cancer (HNC) in sensing food taste. 18 suggests that olfaction has a significant role in food taste.

Treatment Summary

Olfactory training is an effective treatment for olfactory dysfunction. 11 Platinum-based chemotherapy may provide an additional therapeutic benefit for patients with anosmia secondary to nasal polyposis. 10 Photobiomodulation (PBM), Transmucosal Laser Irradiation of Blood (TLIB), and B complex might be treatment options in the management of COVID-19 Related Long-Term Taste Impairment (CRLTTI). 5 Cerebrolysin therapy, a NTF, and olfactory and gustatory trainings are also potential treatment options for persistent post-COVID-19 smell and taste disorders. 4

Benefits and Risks

Benefit Summary

Olfactory training is a well-established treatment for individuals with olfactory dysfunction. 6 Platinum-based chemotherapy may provide an additional therapeutic benefit for patients with anosmia secondary to nasal polyposis. 10 Photobiomodulation (PBM), Transmucosal Laser Irradiation of Blood (TLIB), and B complex might be treatment options in the management of COVID-19 Related Long-Term Taste Impairment (CRLTTI). 5 Cerebrolysin therapy, a NTF, and olfactory and gustatory trainings are also potential treatment options for persistent post-COVID-19 smell and taste disorders. 4

Risk Summary

Patients should be informed of the potential consequences of chemotherapy-induced taste and smell changes, including poor weight gain, food aversion, emotional distress, and an overall decrease in quality of life, prior to starting treatment. 10

Comparison Between Studies

Commonalities

Several studies highlight the impact of taste and smell disorders on quality of life, particularly in those undergoing cancer treatments or experiencing COVID-19 infection. The research underscores the need for effective treatments and strategies to manage these conditions.

Differences

The research studies differ in terms of target populations, interventions used, and findings. Some studies investigated the efficacy of specific treatments while others focused on the prevalence and factors associated with taste and smell disorders.

Consistency and Discrepancies in Results

The research consistently indicates the potential for taste and smell disorders to be induced by cancer treatments and COVID-19 infection. However, there is a need for further investigation to determine the most effective treatment options for these disorders due to the varying results across studies.

Real-World Applications and Considerations

Taste and smell disorders can be a significant challenge for individuals undergoing cancer treatment or recovering from COVID-19. Olfactory training has shown promise as a treatment for olfactory dysfunction. 6 Platinum-based chemotherapy may provide an additional therapeutic benefit for patients with anosmia secondary to nasal polyposis. 10 Photobiomodulation (PBM), Transmucosal Laser Irradiation of Blood (TLIB), and B complex might be treatment options in the management of COVID-19 Related Long-Term Taste Impairment (CRLTTI). 5 Cerebrolysin therapy, a NTF, and olfactory and gustatory trainings are also potential treatment options for persistent post-COVID-19 smell and taste disorders. 4 Further research is crucial to identify the most effective treatment options for taste and smell disorders as results vary across studies.

Limitations of Current Research

Many of the studies are relatively small and provide limited information on long-term outcomes. Larger, long-term studies are needed to better understand the most effective treatments for these disorders.

Future Research Directions

Further research is needed to identify effective treatments for taste and smell disorders. Studies should focus on investigating the underlying causes of these disorders and developing novel therapies. It is also crucial to investigate the long-term impact of these disorders and to develop strategies for improving the quality of life for individuals experiencing them.

Conclusion

Emerging research suggests that taste and smell disorders can be induced by cancer treatments and COVID-19 infection, highlighting the need for effective treatment options. The optimal treatment approach for these disorders is currently not clear, as results vary across studies. Larger, long-term studies are needed to identify the most effective treatment strategies.

It is important to prioritize the prevention and treatment of taste and smell disorders, as these conditions can have a significant impact on a patient's quality of life.

Treatment List

Olfactory training, Platinum-based chemotherapy, Photobiomodulation (PBM), Transmucosal Laser Irradiation of Blood (TLIB), B complex, Cerebrolysin therapy