Chapter 6: Discussion
This chapter discusses the results from the assessments carried out on the validity of screening hearing tests for early detection of ototoxicity among children with cancer. Ototoxicity monitoring has grown increasingly important in recent times as more concerns have been raised over hearing defect side effects associated with cancer therapy. Audiological monitoring of ototoxicity is carried out primarily for early detection of changes to hearing status usually attributed to therapy with the aim of changing the treatment regime to reduce chances of loss of hearing by the patient. Ototoxicity monitoring is important for early identification as well as early intervention in case of therapy related defects. In the past few decades, two main methods have been relied upon for audiologic monitoring of ototoxicity in patients; these include high frequency audiometry (HFA), and otoacoustic emission (OAE) measurement. These methods vary in their utilization and reliability. The methods can be applied separately or in combination for different patient populations.
A study by Fausti et al. (1994) examining the same concepts as this study has indicated that High-Frequency Audiometric monitoring for early detection of ototoxicity work effectively and are quite important. The study proceeds to link the success of this method to its relative reliability in detecting and screening ototoxicity in cancer patients. The study by Fausti et al. (1994) and similar continuing investigations have been conducted to establish the reliability of HFA and OAE as ototoxicity diagnosis and screening procedures. All these studies have found the two methods to be good for both diagnosis and screening at various different sound frequencies depending on the patient.
Summary of Findings
With time, HFA and OAE have become increasingly well established as ototoxicity tests particularly for first level testing or monitoring of patients under treatment with potentially ototoxic drugs. These methods have gained prominence because of their flexibility, ease of application and their cost effectiveness. This study set out to investigate the association between the two tests above and a standard clear tone audiometric test which is considered the gold standard test. The study also investigated the validity of the tests using a sample of children and went on to measure the reliability of each of the tests.
In summary, this study indicates that just like the control gold standard Screening Pure Tone Audiometry, all the four ototoxicity tests applied in the test for audiometry in children in the study were relatively reliable and relevant for that purpose. The study revealed that Diagnostic High Frequency Audiometry (DHFA), Screening High Frequency Audiometry (SHFA), Diagnostic Distortion Product Autoacousic Emissions (DDPOE), and Screening Distortion Product Autoacousic Emissions (SDPOE) were all realiable tests for ototoxicity in children undergoing therapy for cancer. The study also tested the association between all the four tests and the Standard Pure Audiometry Test (SPTA) with the main outcome being that all the tests were associated with the SPTA. Since the latter is an established reliable test for ototoxicity, it is generally concluded that all the four tests can be successfully used for the test too. This study also measured the validity of the tests and their ototoxicity results using ROC measurements. The main outcome of the validity test was that all the tests were valid to a high degree. This implies that the ototoxicity outcomes of the cancer patients can be considered as valid and reliable for physician decision support. Finally the study also examined the agreement between the tests using the Kappa statistic measurement, this was especially important for the diagnosis and screening tests to show whether they agreed with each other or not. It was revealed that the association between DHFA and SHFA as well as that between DDPOE and SDPOE is very close.
In all the tests carried out in this study, it is evident that the most important factor being examined is the reliability of the test in ototoxicity measurement. This is in appreciation of the fact that for ototoxicity diagnosis and screening to be accurate and useful, the results of a test have to be reliable. Similar studies have also examined reliability in High Frequency Autometry and Distortion Product Autoacousic Emissions tests. Beahan et al. (2012) carried out High-Frequency Audiometry in Children in a procedure aimed at establishing the reliability of the test in ototoxic criteria determination. Like in this study, children were preferred for their study mainly because investigations involving children are scant and there is need to enrich literature concerning ototoxicity in children. Basically, reliability of the HFPTA in measuring ototoxicity children was the main objective of the study, just like it is in this study. The findings of the study by Beahan et al. (2012) indicated that HFPTA was generally reliable at different frequency thresholds across test-retest conditions for children of all age groups. Similar results have also been obtained for HFA in this study; the tests have been demonstrated to be generally reliable. Similarly, a study by Sockalingam et al. (2007) examined the test-retest reliability of DPOE in children with normal hearing under cancer treatment. The main finding was that the test is reliable in determining ototoxicity in children, just like it has been established in this study. Sockalingam et al. (2007) also indicated in their study that several investigations of DPOAE levels in repeated measurements have reported excellent within-subject reliability. The findings from all the studies mentioned above are in agreement with the findings in this study indicating that the ototoxicity test under examination can generally be considered to be reliable.
This study established that the greatest proportion of all the patients (children) involved in the tests was made up of male children. Males constituted 62.5% of the whole population while females made up the remaining 37.5% of the total population tested. This implies that the average number of male children diagnosed with cancer is much greater than that of girls in the hospital where the study was carried out.
All the 32 patients recruited for the study were included in the study, none of them were excluded. This can be attributed to the fact that all the recruited 32 patients were within the inclusion criteria. All of them were under therapeutic treatment for cancer and they were located in the same establishment. The fact that the parents of all the children included were ready to let their children get involved in the study indicates awareness about the importance of cancer research in general and particularly the importance of ototoxicity test towards the preservation of hearing ability in patients being treated for cancer.
This study also established that about 50% of all the children included in the study were aged between 5 and 8 years. A further 25% of the children were between the age of 1 year and 4 years making up a total of 75% of all children involved in the study 8 years and below. This finding implies that most children are diagnosed with cancer at a young age and that most of the children patients under treatment are very young.
Test of Association
The chi-squared test is a test of association between different variables. According to Indrayan (2008) Chi-square tests are widely applied in medical statistical research to determine if there are relationships between tests or variables under investigation. The tests are also used to measure the significance of statistical relationships between two medical tests, or two populations if a relationship is established between them (DeLong et al., 1998). In this study, Chi-square has been used to measure relationships between the various ototoxicity tests to determine their viability. The Standard Pure Audiometry Test (SPTA) was used as the control test in this study (the gold standard) to measure the validity of the other tests. Basically, association between the SPTA and another test would indicate that this test was valid.
First, the chi-square test was used to test for association between ototoxicity findings with Standard Pure Audiometry and those with Diagnostic High Frequency Audiometry (DHFA). The result of the Chi-square test revealed that there was a significant statistical relationship between ototoxicity with SPTA and ototoxicity with DHFA. It can therefore be concluded from that finding that this association suggests the ability of DHFA to diagnose ototoxicity in patients. The second test involved measuring of association between ototoxicity results with SPTA and ototoxicity results with Screening High Frequency Audiometry (SHFA). The results indicated indicated that Screening High Frequency Audiometry produced similar ototoxicity findings as those of screening with Standard Pure Tone Audiometry, there was a significant statistical relationship between ototoxicity with SPTA and ototoxicity with Screening High Frequency Audiometry. This association also indicates that SHFA can be successfully used as an ototoxicity screening test for patients undergoing cancer therapeutic treatment.
Basically, DHFA is applied for first diagnostic test to determine whether a patient is exhibiting positive ototoxicity, on the other hand SHFA is a screening test that is important in not only confirming ototoxicity in patients that have already been diagnosed but also for determination of the extent of ototoxicity if possible. Significant association between the two tests and the gold standard SPTA indicates that the two procedures are viable as good ototoxicity diagnostic and screening tests.
The third association test involved testing for association between ototoxicity with SPTA and ototoxicity with Diagnostic Distortion Product Otoacoustic Emission (DDPOE). DDPOE serves more or less the same function as DHFA, that of diagnosing ototoxicity among patients on cancer therapy. This study established that that there was a significant statistical relationship between ototoxicity with SPTA and ototoxicity with Diagnostic Distortion Product Otoaoustic Emissions. This indicates that this diagnostic test is viable as it shows association with the SPTA ototoxicity test, which is the standard measure. Similarly, tests were carried out to determine the association between ototoxicity with SPTA and ototoxicity with Screening Distortion Product Otoacoustic Emission (SDPOE). The result of the Chi-square test indicated that was is a significant statistical relationship between ototoxicity with SPTA and ototoxicity with Screeening Diagnostic Distortion Product Otoaoustic Emissions. This association also indicates that this diagnostic test is viable as it shows association with the SPTA ototoxicity test, which is the standard measure.
After carrying out association tests between the gold standard and the other tests under examination in this study, a test of association was carried out between the diagnostic tests and the screening tests for both HFA and DPOE. Chi-square results between Diagnostic High Frequency Audiometry and Screening High Frequency Audiometry indicate that there was a significant statistical relationship between ototoxicity with Diagnostic High Frequency Audiometry and ototoxicity with Screening High Frequency Audiometry. This association between the diagnostic and screening test further confirms that both the tests are viable as measures of ototoxicity in patients. The second test involved comparison between ototoxicity with Diagnostic Distortion Product Otoacoustic Emissions and ototoxicity with Screening Distortion Product Otoacoustic Emissions. Results revealed that there was a significant statistical relationship between the two of them. This association between them also indicated their strength as good tests for ototoxicy in cancer patient under therapy.
Validity of Tests
Experimental validity is a very important in any medical experimental tests to ensure that they are valid for correct decision making. Experimental validity can be described as the extent to which a finding is genuine. The most convincing evidence that suggests that a test or process has good experimental validity is if it is established that its findings can be replicated in other studies or if it can produce the same findings if repeated severally.
In this study, test for validity was carried out through measurement of the Receiver Operating Characteristic (ROC). ROC curves have commonly application in medicine for determination of cutoff values for a clinical test (Hajian et al., 1997). The ROC is a measure of goodness-of-fit often used to evaluate the fit of a logistic regression model is based on the simultaneous measure of sensitivity. In this study the measure of sensitivity of the study is associated with the test’s validity. The test was used to determine the sensitivity and specificity of both the High Frequency Pure-tome Audiometry tests (Diagnostic and screening) as well as that of Distortion Product Otoacoustic Emissions tests (Diagnostic and screening), to determine the most sensitive and specific test between the two types.
In the case of the HFPA test, the ROC curve revealed that the area under the curve was significantly closer to the absolute (1) and that the result was statistically significant. An area of 0.839 indicates that the test is valid and sensitive enough to produce valid ototoxicity results. Similarly, the results of the DHFPA test for validity revealed that the area under the curve was significantly closer to the absolute and that the result was statistically significant. An area of 0.807 indicates that the test is valid and sensitive enough to produce valid ototoxicity results. For the Screening Distortion Product Otoacoustic Emissions test, the ROC curve indicated the area of the curve as being 0.816 and being significant. This means that the test is also valid for measurement of ototoxicity results as it is significantly sensitive. For the Diagnostic Distortion Product Otoacoustic Emissions test, examination of validity using ROC indicated that the test was both valid therefore sensitive to ototoxicity measurements. The area under the curve in this case was 0.761.
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