Abstract
Objective
Total laryngectomy, a procedure that permanently separates the upper and lower airways and requires patients to breathe through a stoma, significantly impacts olfactory function owing to the lack of nasal airflow. This prospective cohort study aimed to investigate the reduction in olfactory function following total laryngectomy and determine the association between clinical characteristics and olfactory impairment.
Methods
A prospective cohort study was conducted among 40 patients (aged 44–82 years) undergoing total laryngectomy at the University Medical Center Ho Chi Minh City, Vietnam, from November 2023 to April 2025. Olfactory ability was assessed before and after surgery using the Sniffin’ Sticks test, including threshold, discrimination, and identification components, which were used to calculate a total threshold, discrimination, and identification score. Additionally, clinical characteristics were analyzed for potential associations with olfactory impairment.
Results
Prior to surgery, objective olfactory testing revealed that 82.5% of the patients had normosmia, and 17.5% exhibited hyposmia. Following surgery, all patients experienced olfactory impairment, with 87.5% presenting with complete anosmia. There was a statistically significant decline in olfactory function after total laryngectomy (p < 0.001, Wilcoxon signed-rank test). Multivariable regression analysis revealed no statistically significant associations between the clinical characteristics evaluated and postoperative olfactory impairment.
Conclusions
Olfactory impairment is a common and significant consequence of total laryngectomy, leading to substantial reductions in patients’ quality of life. The primary causes include loss of nasal airflow and potential structural changes in the olfactory mucosal epithelium. This highlights a universal risk because our analysis did not identify any specific clinical variables that were significantly associated with olfactory impairment. These findings underscore the critical need for standardized preoperative counseling and the implementation of postoperative olfactory rehabilitation strategies for all patients undergoing total laryngectomy.
Introduction
Background
Head and neck squamous cell carcinoma is the sixth most common cancer globally, with laryngeal cancer accounting for approximately one-third of all cases; it predominantly affects males, with a male-to-female ratio of 6:1. Tobacco use and alcohol consumption are the two principal etiological factors, contributing to over 95% of the cases. 1
The management of laryngeal cancer is multifaceted and tailored based on the subsite, extent, and volume of the primary tumor as well as the presence of lymph node metastases; treatment often involves surgery, radiation therapy, chemotherapy, and combined modality therapy. 2 Surgical treatment options range from minimally invasive microlaryngeal techniques to total laryngectomy (TL), the most extensive surgical intervention. TL is frequently considered the standard of treatment for advanced disease owing to its favorable oncological outcomes. 3 However, this procedure permanently separates the upper and lower respiratory tracts, requiring patients to breathe through a stoma. This anatomical alteration prevents inhaled air from traversing the nasal passages, thereby impeding the transport of odorant molecules to the olfactory epithelium, resulting in hyposmia (reduced sense of smell) or anosmia (complete loss of smell). 4 This impairment significantly impacts patients’ quality of life, diminishing the ability to perceive environmental scents and increasing their vulnerability to hazards such as undetected gas leaks or spoiled food. 5
Over the past two decades, numerous studies have consistently reported a high prevalence of olfactory impairment following TL, with rates of hyposmia or anosmia ranging from 70% to 100%.6–9 Despite this substantial body of evidence globally, there remains a notable scarcity of research on this condition among Vietnamese patients. This knowledge gap highlights the need for context-specific data to better understand and address this important clinical issue in Vietnam.
Objectives
The primary objective of this study was to determine the extent of olfactory impairment among patients who have undergone TL. The secondary objective was to evaluate the potential association between the presence and severity of olfactory impairment and various clinical characteristics of these patients.
Methods
This prospective observational study represents the initial phase of a larger research project focused on olfactory rehabilitation. This study was reported in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement.
Setting
The study was conducted at the Department of Otorhinolaryngology, University Medical Center Ho Chi Minh City, Vietnam, from November 2023 to April 2025.
Participants
Recruitment and selection
Consecutive patients diagnosed with primary laryngeal or hypopharyngeal carcinoma scheduled for TL at our institution between November 2023 and April 2025 were prospectively identified. Eligible individuals were screened based on the following criteria.
The inclusion criteria were as follows:
Age ≥18 years at the time of enrolment; Confirmed pathological diagnosis of primary laryngeal or hypopharyngeal carcinoma; Indication for TL; Willingness and ability to complete psychophysical olfactory assessments at both baseline (preoperatively) and/or 3 months postoperatively.
The exclusion criteria were as follows:
History of pre-existing neurodegenerative disorders (e.g. Parkinson’s disease and Alzheimer’s disease) or other neurological conditions known to affect olfaction; Psychiatric conditions or cognitive impairment interfering with patient cooperation during olfactory testing; History of nasal or sinus surgery or significant head trauma that could have caused olfactory epithelial damage; Evidence of disease recurrence or severe postoperative complications preventing the 3-month postoperative assessment.
Assessments and follow-up
Baseline olfactory function was assessed in the preoperative period. Following TL, patients received standard clinical care. Olfactory function was re-evaluated during a scheduled follow-up visit approximately 3 months postoperatively. This time point was selected to ensure a stable postoperative medical status, characterized by healed surgical wounds, resumption of normal oral intake, and absence of postoperative complications affecting olfactory testing.
Variables
The outcome variables were as follows: 1. Primary outcome. The primary outcome was postoperative olfactory function, assessed psychophysically at approximately 3 months after TL. Olfactory function was measured using the Sniffin’ Sticks test, yielding a continuous threshold (T), discrimination (D), and identification (I) (TDI) score (sum of threshold, discrimination, and identification scores). 2. Baseline outcome. The baseline outcome was preoperative olfactory function, assessed psychophysically prior to TL using the same Sniffin’ Sticks test, yielding a continuous TDI score. This served as a baseline measure for comparison and analysis of change. 3. Secondary outcome. The secondary outcome was self-perceived impact of olfactory impairment on the quality of life, assessed at 3 months postoperatively using a visual analog scale (VAS), with scores ranging from 0 (no impact) to 10 (maximum impact), and the Questionnaire of Olfactory Disorders–Negative Statements (QOD-NS). 10
Diagnostic criteria for olfactory function categories
Based on the TDI scores obtained from the Sniffin’ Sticks test, olfactory function was categorized into the following three groups: normosmia (TDI score, 41.25–30.75), hyposmia (TDI score, 30.5–16.25), and anosmia (TDI score ≤16). 11
Exposures and predictor variables
Patient demographic, clinical, and treatment characteristics were evaluated as exposures and predictors of postoperative olfactory function. These included age (years), sex, body mass index (BMI), smoking history (pack-years), alcohol consumption (yes/no), history of coronavirus disease 2019 (COVID-19), comorbidities, history of sinus surgery/head trauma, radiotherapy before surgery (yes/no), endoscopic findings of the olfactory cleft features (including nasal mucosa status, nasal discharge, presence of nasal polyps, and septal deviation), and baseline olfactory function (continuous TDI score and categorical status).
Data sources and measurement
Olfactory function assessment
Olfactory function, serving as both baseline (preoperative) and primary (postoperative) outcomes, was measured using the standardized Sniffin’ Sticks test (Burghart Messtechnik, Germany). The assessment was performed identically for both preoperative (baseline) and follow-up (approximately 3 months postoperative) evaluations. Assessments were conducted in a quiet, well-ventilated room under standardized conditions. Patients were instructed to abstain from eating, drinking, or smoking for at least 15 min before the test. The test included the following three sub-tests: 1. Threshold (T). This test involved 16 triplets of odor pens with progressively decreasing concentrations of n-butanol. Patients were required to correctly identify the pen containing the odor in each triplet. 2. Discrimination (D). This test assessed the patients’ ability to differentiate the pen with a distinct odor among a triplet of pens. 3. Identification (I). This test evaluated the patients’ ability to recognize and name 16 common odorants presented in felt-tip pens. Identification was conducted via a four-alternative forced-choice task from the provided descriptor lists.
Scores from each component were recorded and summed to yield the cumulative TDI score. Identical methodology was applied at both preoperative and 3-month postoperative evaluations for the same individuals, ensuring direct comparability of olfactory function measurements within the cohort over time.
Bias
Potential sources of bias and study limitations were considered and addressed. A primary limitation was the absence of baseline (preoperative) olfactory function data for 10 patients enrolled post-TL, precluding individual pre–post analysis for this group. These patients were included only in analyses that did not require baseline measurements. General selection bias was minimized by recruiting consecutive eligible patients preoperatively, applying uniform inclusion and exclusion criteria. Information bias was mitigated using standardized, validated measurement instruments (Sniffin’ Sticks, VAS, and QOD-NS) administered under controlled conditions by trained personnel and employing standardized data collection methods to obtain data from medical records and endoscopic evaluations. Potential attrition bias was addressed by maintaining close contact with the participants and offering flexible follow-up scheduling.
Study size
The study size was determined based on the number of consecutive eligible patients undergoing TL at our institution between November 2023 and April 2025, resulting in a cohort of 40 patients. This sample represented the total available population meeting the eligibility criteria during the defined study period. Although this cohort size provides sufficient data for describing the prevalence and characteristics of postoperative olfactory impairment, we acknowledge that the determination of robust, statistically significant associations with multiple predictors using regression analysis would ideally require a larger sample. Analyses exploring associations primarily utilized univariable or limited bivariable methods. The absence of baseline data for 10 patients enrolled after TL further reduced the sample size for analyses requiring baseline measurements. Data from this cohort will inform the design and sample size calculation in future studies powered for multivariable analysis.
Quantitative variables
Quantitative variables included in the analyses were age (years), BMI (kg/m2), smoking history (pack-years), baseline olfactory function (continuous TDI score), postoperative olfactory function (continuous TDI score), and self-perceived impact (VAS score).
These variables were summarized using descriptive statistics and presented as mean ± SD or median (interquartile range), based on data distribution. The normality of data distribution was assessed using the Shapiro–Wilk test.
In analytical models, these variables were primarily treated as continuous predictors or outcomes, as appropriate. However, for specific analyses or enhanced clinical interpretability, several quantitative variables were categorized as follows: 1. Age was categorized using a cutoff of 63 years, based on the median age of the cohort. 2. BMI was categorized into the following three groups: underweight (<18.5 kg/m2), normal (18.5–25 kg/m2), and overweight/obese (≥25 kg/m2), based on the World Health Organization classifications. 3. Smoking history, recorded as pack-years, was categorized into the following three levels: low (<20 pack-years), medium (20–40 pack-years), and high (>40 pack-years), based on thresholds used in the literature on smoking-related risks. 12
Olfactory function (TDI score) was also utilized as a categorical variable (normosmia, hyposmia, and anosmia) according to the predefined diagnostic criteria described in the Diagnostic Criteria section.
These quantitative variables were categorized to facilitate the exploration of associations using appropriate statistical tests with the available sample size and enhance the clinical interpretability of the findings.
Statistical analyses
Statistical analyses were performed using R (version 4.4.1), with p values <0.05 (two-sided) considered to indicate statistical significance.
The primary objective was addressed by reporting postoperative olfactory status (prevalence of normosmia/hyposmia/anosmia) using descriptive statistics (frequencies/percentages) and comparing preoperative versus 3-month postoperative continuous TDI scores using the Wilcoxon signed-rank test.
To explore associations for the secondary objective, univariable tests (chi-squared, Fisher’s exact, or Kruskal–Wallis tests) were utilized. Exploratory multivariable logistic regression was performed to evaluate the relationship between baseline clinical characteristics and postoperative olfactory impairment.
Missing baseline olfactory data for 10 patients who underwent TL were excluded from the analyses requiring baseline measurements; for other missing data, complete case analysis was used. Loss to follow-up and sensitivity analyses were addressed as described in the “Bias” subsection.
Results
Participants
The flow of participant selection throughout the study is presented in Figure 1. During the study period, 40 consecutive eligible patients were enrolled. All participants completed the 3-month postoperative assessment, resulting in no loss to follow-up. However, as baseline objective olfactory data were only available for 30 individuals, the sample size for specific pre–post analyses was limited to this subgroup.
Flowchart of participant selection throughout the study.
Demographic and clinical characteristics
The detailed baseline characteristics of the 40 study participants are presented in Table 1. The cohort primarily comprised male patients (N = 40, 100%), with a mean age of 63 ± 8.02 (44–82) years. Consistent with disease risk factors, smoking history (100%) and alcohol consumption (65%) were highly prevalent. Hypertension was the most common comorbidity (52.5%). Endoscopic evaluation indicated generally healthy olfactory clefts, with mostly pink mucosa, absence of polyps, minimal secretions, and septal deviation observed in a minority of patients. Five patients received preoperative radiotherapy, with a median interval of 3.5 months from the time of radiotherapy completion to olfactory assessment after TL.
Baseline demographic and clinical characteristics of study participants (N = 40).
COVID-19: coronavirus disease 2019.
Olfactory function before surgery (baseline)
Baseline olfactory function was assessed preoperatively for all 40 participants. Objective testing using the standardized Sniffin’ Sticks test was performed for 30 patients. For the remaining 10 patients, whose assessments were based on subjective reporting because they had undergone TL prior to study commencement, baseline function was documented as normal.
The results of objective assessment for the 30 patients evaluated are presented in Table 2. The median scores for the threshold (T), discrimination (D), and identification (I) components were 9.13, 12.00, and 12.00, respectively, yielding a total median TDI score of 32.50.
Comparison of objective olfactory function scores before and 3 months after total laryngectomy (N = 30).
p-values were calculated using the Wilcoxon signed-rank test.
TDI: threshold, discrimination, and identification.
Based on the available baseline data for all 40 participants (30 objective and 10 subjective categorized as normosmia), classification revealed that 82.5% (n = 33) of them presented with normosmia and 17.5% (n = 7) with hyposmia (Table 3). No cases of anosmia were observed at baseline. These 10 patients were included in the overall preoperative prevalence calculation but were excluded from the paired pre- and postoperative statistical comparison, which was restricted to the 30 patients with objective data available for both time points.
Preoperative and postoperative olfactory function status (N = 40).
Olfactory function after surgery
Postoperative olfactory function was assessed for all 40 participants approximately 3 months postoperatively using subjective measures (VAS and QOD-NS score) and the objective Sniffin’ Sticks test. The results are presented in Table 2.
Subjective assessment revealed severe olfactory impairment. The median VAS score was 9.0, with 12 patients reporting complete anosmia, indicating profound perceived olfactory loss. The median QOD-NS score was 14 out of 51, highlighting a substantial impact on quality of life.
The objective Sniffin’ Sticks test showed severely reduced scores. The median scores were as follows: threshold (T), 2.00; discrimination (D), 6.00; and identification (I), 6.00. The total TDI score was 14.38 (8.50–19.50).
Classification based on objective results (Table 3) showed a high prevalence of severe olfactory impairment, with 87.5% (n = 35) of the patients exhibiting anosmia and 12.5% (n = 5) showing hyposmia. No normosmia was observed at this time point. In summary, all 40 patients (100%) exhibited a reduction or loss of smell following TL.
Comparison of preoperative and postoperative olfactory function
Postoperatively, among 30 patients with paired objective olfactory test data, the total TDI score and each component score were significantly lower than their corresponding preoperative values (p < 0.001; Wilcoxon signed-rank test). These findings indicate a substantial decline in olfactory function following TL, as shown in Table 2.
Additional analyses
Exploratory multivariable logistic regression revealed that demographic or clinical features showed no significant association with postoperative loss of olfactory ability (Table 4). Due to the limited sample size, formal subgroup and interaction analyses were not conducted as they would lack sufficient statistical power. Sensitivity analyses were performed to assess the robustness of the main findings, and the results were generally consistent with those of the primary analysis, indicating the overall stability of the observations.
Exploratory multivariable logistic regression analysis of factors associated with postoperative anosmia.
COVID-19: coronavirus disease 2019.
Discussion
Key results
This study, conducted among 40 patients undergoing TL, aimed to investigate postoperative olfactory impairment and its associated factors. Key findings included the baseline characteristics of the cohort (Table 1), preoperative olfactory function status, and a high prevalence of severe olfactory impairment observed at 3 months postoperatively (Tables 2 and 3), consistent with a significant decline in olfactory function compared with that at baseline (Table 2). Exploratory association analyses, however, did not identify an independent association of any baseline demographic or clinical factor with postoperative olfactory impairment (Table 4).
Interpretation and comparison with previous findings
Demographic and clinical characteristics
The study consisted of 40 male patients who underwent TL, reflecting the predominance of laryngeal cancer among males, 13 which is attributed to the higher prevalence of smoking and alcohol consumption among them. 7 The average patient age was 63 years, with most participants aged 61–70 years, consistent with previous epidemiological data.6,7,9 The mean BMI was 21.35 kg/m2, with most patients falling in the normal-weight category.
The clinical profile of our cohort was notably different from those reported by previous studies. The prevalence of hypertension (52.5%), the most common comorbidity in our study, was significantly higher than that reported by Subbaraj et al. 14 (16.67%). Similarly, our postoperative nasal endoscopy findings indicated generally healthier mucosal conditions than those observed by Riva et al., 8 who noted a higher incidence of serous nasal discharge in their cohort. Such discrepancies in both systemic comorbidities and local sinonasal health are likely multifactorial, stemming from variations in study populations, geographical factors, and clinical management protocols across different centers.
Olfactory function before surgery
A key strength of our study was the assessment of preoperative olfactory function, a step often omitted in other research studies. We found that the majority of our patients (82.5%) had normal olfaction, and only 17.5% experienced hyposmia preoperatively, with a median TDI score of 32.50. This contradicts the findings reported by Subbaraj et al., 14 who assessed the olfactory function of 42 patients before and 2 weeks after surgery using a two-component olfactory test (threshold (T) and identification (I)). They reported a mean preoperative total score of 4.17 ± 1.39 (range, 1.0–6.5), with most patients classified as having moderate hyposmia (53%). The rationale for this decline may be attributed to factors such as age, smoking history, other environmental influences, and previous radiation exposure. Their results differed from those of our study, which could be due to the use of different objective olfactory assessment methods and distinct categorization of olfactory characteristics based on total component scores as well as the absence of preoperative data for some patients in our cohort who had already undergone TL before study initiation. Establishing this baseline was crucial, as it allowed precise quantification of the profound postoperative decline in olfactory function.
Postoperative olfactory function and its comparison with preoperative status
TL causes a significant impairment of olfactory function due to the disconnection between the upper and lower respiratory tracts, requiring patients to breathe through a permanent tracheostomy. This disruption leads to the loss of airflow through the nasal passages, preventing odorant molecules from reaching the olfactory epithelium, which is the primary cause of olfactory impairment.8,15 Furthermore, some studies have indicated that the chronic absence of nasal airflow can lead to secondary structural changes in the olfactory mucosal epithelium, including epithelial degeneration, squamous metaplasia, or alterations in nasal mucus production, which may contribute to postoperative olfactory impairment. 4
In this study, the median postoperative total TDI score was 14.38, with 87.5% of the patients experiencing anosmia and 12.5% exhibiting hyposmia, indicating a significant decline in the score compared with that before surgery (p < 0.001). This result is consistent with that reported by Riva et al., 8 wherein all patients experienced olfactory impairment following TL. Assessment using the Sniffin’ Sticks test confirmed that the threshold (T), discrimination (D), and identification (I) scores as well as total TDI score in the postoperative group were significantly lower than those in the control group (p < 0.05). Similarly, Ward et al. 16 also investigated the impact of TL on olfactory function, quality of life, and communication abilities over a 3-year follow-up period among 43 patients. Utilizing the Scandinavian Odor-Identification Test (SOIT), researchers have found statistically significant differences in the average SOIT scores between the laryngectomy and control groups at 6 and 36 months post-intervention (p < 0.05). These results highlight the persistent negative impact of TL on olfactory function.
Olfactory loss adversely affects the quality of life, leading to anxiety and a sense of insecurity because patients are unable to detect warning odors such as those from smoke, gas, or spoiled food. Additionally, difficulties in identifying body odors can lead to feelings of embarrassment, social communication limitations, and increased feelings of isolation. Anosmia also impacts mental health because individuals lose connection with memories associated with familiar scents. Moreover, the diminished ability to enjoy food poses challenges to eating habits and increases the risk of nutritional deficiencies. Cooking becomes a stressful activity as patients cannot ensure food quality or accurately season dishes.17,18 In our study, the median total score on the QOD-NS was 14 out of a maximum score of 51, reflecting the profound impact of olfactory impairment on quality of life. Similarly, Risberg-Berlin et al. 19 analyzed 24 patients using the Questionnaire on Olfaction, Taste, and Appetite and demonstrated significant differences in the quality-of-life questionnaire scores between the TL and control groups, aligning with our findings.
The profound impact of olfaction loss on patient safety and quality of life necessitates a proactive clinical approach. Our findings strongly advocate the integration of olfactory management into the standard care for TL patients. This includes comprehensive preoperative counseling about the high likelihood of anosmia to manage expectations and reduce distress. Postoperatively, early olfactory rehabilitation is crucial. Evidence-based interventions such as the Nasal Airflow-Inducing Maneuver (NAIM) have shown efficacy in helping patients draw air through the nasal passages. 20 This can be complemented by structured olfactory training to promote neuroplasticity. Implementing such programs can significantly mitigate the psychosocial burden of olfactory loss. Our group is currently conducting interventional studies to assess the long-term efficacy of these techniques in our patient population.
Regarding baseline factors, our exploratory multivariable logistic regression found no significant association of any variables with the development of postoperative anosmia (Table 4). This finding aligns with that of a recent observational study by Bee et al., 21 who also reported the lack of any association between patient demographics, disease, or treatment variables and poor olfactory outcomes in patients who have undergone TL. This consistency across studies, despite our limited sample size (N = 40), which inherently restricts statistical power and may mask true associations, suggests a profound impact of surgery (nasal airflow diversion) as the primary determinant, potentially overshadowing the influence of baseline factors. It is also plausible that unmeasured factors contribute to residual confounding. Nevertheless, the high prevalence of severe olfactory impairment consistently observed across cohorts highlights a significant risk for all patients, emphasizing the need for universal counseling and rehabilitation strategies.
Limitations
This study has several limitations that should be considered. The relatively small sample size (N = 40) inherently limited the statistical power required for exploratory analyses and may have resulted in less precise effect estimates. Information bias could have stemmed from the reliance on subjective reports for baseline olfactory function in 10 patients, potentially underestimating baseline impairment prevalence. The cross-sectional postoperative assessment at 3 months could not capture temporal changes in olfactory function. Furthermore, the exploratory nature of association analyses with limited power indicates that residual confounding cannot be ruled out, and independent predictors could not be definitively identified.
Generalizability
The generalizability of these findings should be carefully considered. As a single-center study with a relatively small sample size (N = 40), the results may not be fully representative of all patients undergoing TL across different geographical regions or healthcare settings. Variations in surgical techniques, postoperative care protocols, and environmental factors across centers could also influence olfactory outcomes and the applicability of these results. Despite these limitations, the use of standardized and validated assessment tools (Sniffin’ Sticks, VAS, and QOD-NS) facilitates comparison with other studies and may support some degree of generalizability regarding the overall nature and burden of olfactory impairment in this patient group.
Conclusion
Olfactory function is profoundly impaired in patients who have undergone TL, leading to a high rate of functional anosmia that markedly diminishes patient safety and quality of life. Although the primary cause is the surgical diversion of nasal airflow, potential secondary changes to the olfactory epithelium may also play a contributing role. Our findings in a Vietnamese cohort confirm the universal nature of this impairment and highlight a critical gap in clinical care protocols. Therefore, it is imperative that olfactory assessment and management become a standard component of care for laryngectomy patients. Clinicians should provide systematic preoperative counseling and proactively implement postoperative rehabilitative interventions, such as the NAIM and structured olfactory training, to help restore this vital sense and improve patients’ overall well-being.
Footnotes
Acknowledgements
The authors would like to express their sincere gratitude to Dr Le Thao Ngoc Nhi, biostatistician, for her invaluable support and expert review during the data analysis and processing of this study.
Author contributions
L.X.Q: conceptualization, methodology, and project administration. T.T.T.: investigation, data curation, formal analysis, and writing—original draft. L.H.D: supervision, project administration, writing—review & editing, and funding acquisition. All authors have read and approved the final manuscript.
Consent to participate
Written informed consent was obtained from all participants prior to their inclusion in the study.
Consent for publication
Not applicable.
Data availability
The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.
Declaration of conflicting interest
The authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Ethical considerations
This study was approved by the Ethics Committee of the University of Medicine and Pharmacy in Ho Chi Minh City (Approval No. 1720/QD-DHYD, Date 23/06/2023).
Funding
This research was funded by the University of Medicine and Pharmacy at Ho Chi Minh City, under contract number 83/2025/HD-DHYD, dated 17/04/2025.
