Occupational Noise-induced Hearing Loss Patients: Diffusion Tensor Imaging Study And Resting-state Functional Network Connectivity Study

Part 1 Alterations of cerebral white matter microstructure in patients with occupational noise-induced hearing loss:a diffusion tensor imaging studyObjective:To investigate the alterations of cerebral white matter microstructure among the occupational noise-induced hearing loss(ONIHL)patients by diffusion tensor imaging(DTI),using a tract-based spatial statistic(TBSS)technique to explore the abnormal brain structure and pathological mechanism of ONIHL,to provide some basis theories for clinical earlier prevention.Methods:The study included 122 patients who were primary diagnosed as ONIHL patients by Yantai shan Hospital occupational doctors,enrolling and grouping finally:a mild group(MP,n=79),a relative severe group(including moderate and severe groups;RSP,n=32)and 11 undetermined patients(lost to follow-up),as well as 84 age-and education-matched healthy controls with normal health hearing level(health control,HC).All subjects’ chinical data were collected including age,education level,hearing level,occupation type,the noise exposure time and some scales including Mini-Mental State Examination(MMSE),tinnitus handicap inventory(THI),Hamilton Anxiety Scale(HAMA).Scanning by GE Discovery MR 750 3.0T magnetic resonance equipment underwent the following sequences:the routine brain,inner ear MR examinations,3D-FSPGR brain volume imaging and DTI imaging.Correlation analysis were performed on basic clinical data such as hearing level,noise exposure time and HAMA score.Then,analyzing the DTI imaging by TBSS and obtaining the abnormal DTI parameters among the three groups.Further,by means of covariance analysis,age and education level were introduced as covariables to detect the white matter fiber bundle structure brain regions with differences in DTI parameters among the three groups(P<0.05,voxels>100);After that,Bonferroni test were applied to pairwise comparison of DTI parameters between groups(P<0.0167);Pearson correlation test were used to compare the correlation between DTI parameters and noise exposure time,hearing level,HAMA Scale(P<0.05).In addition,a region of interest(ROI)analysis was used to study the DTI parameters of the bilateral auditory cortex,i.e.,Heschl’s gyrus(P<0.05).Results:The study eventually cohort consisted of 71 MP group,28 RSP group and 75 HC group.There were no statistically significant differences in age,years of education,and MMSE score among the three groups,while there was statistically significant differences in HAMA score among the three groups.All patients(MP and RSP)were mainly engaged in drilling and welding(noise environment above 90dB,ineffective protection).There was no statistically significant differences in THI score between the MP and RSP group;but there were statistically significant differences in noise exposure time,hearing level and HAMA score between the MP and RSP group.Noise exposure time was negatively correlated with hearing level and HAMA score,and the THI score was negatively correlated with hearing level.DTI:1.We found all DTI parameters’values(FA,MD,AD,RD)being statistically significant differences in the left Inferior longitudinal fasciculus(ILF)and left Inferior fronto-occipital fasciculus(IFOF)among the three groups.In addition,The FA value being significantly lower in the bilateral Corticospinal tract(CST),right Fronto-pontine tract(FPT),right Forceps major(FM),left Superior longitudinal fasciculus(temporal part)(SLF),left Cingulum(hippocampus)(C-H)in MP group and RSP groups than in HC group;The AD value shows a diversity changes and being statistically significant in the bilateral CST,left IFOF and right Anterior thalamic radiation(ATR),right External capsule(EC),right SLF,and right Superior cerebellar peduncle(SCP)in MP group and RSP groups than in HC group.2.Then,Bonferroni test and pairwise comparison were performed among the three groups.The FA value,MD value and RD value of the brain regions in the MP and the RSP were statistically significant compared with the HC;while the FA value,MD value and RD value of the brain regions in the MP and the RSP were not statistically significant.The AD value of the brain regions’ pairwise comparison were complicate;there were statistically significant differences in right CST,right EC,right SCP,left IFOF/ILF and right SLF between the MP and the HC;there were statistically significant differences in bilateral CST,right ATR,right EC and right SLF between the RSP and the HC;and there were statistically significant differences in early right ATR and right CST between the MP and the RSP.3.There were significantly negative correlation between the FA and HAMA score in the left IFOF/ILF,right FPT,left SLF and left C-H among the three groups;there were significantly positive correlation between AD and HAMA score in the left IFOF/ILF and right EC among the three groups;there were significantly positive correlation between RD/MD and HAMA score in the left IFOF/ILF among the three groups;and there was a significantly negative correlated between the AD in the right SCP and the noise exposure time.4.There were no significantly in the ROI bilateral auditory cortex among the three groups,the Bonferroni test and pairwise comparison were also not statistically;the AD,MD,RD in the left ROI was significantly negative correlated with the hearing level;but the FA in the right ROI was significantly positive correlated with the HAMA score.Conclusion:1.Our study showed lower FA,higher RD and MD,and higher/lower AD in the ONIHL patients;and the WM micro-structure changes were related to the noise exposure time.It can be speculated that the WM micro-structure changes(myelin and axonal dysfunction)in the ONIHL patients may be related to the noise-induced hearing loss,the mechanism of brain structural reorganization after auditory deprivation and specific brain structural changes or reorganization of brain functional neuroplasticity and noise environment.2.The correlation between hearing level,HAMA score and occupational noise exposure time,and the correlation between THI score and hearing level,suggesting that exposure to noise environment can cause hearing impairment.The DTI parameters of ILF and IFOF among the three groups were significantly correlated with HAMA score.It can be inferred that the anxiety state of ONIHL patients during long-term noise exposure maybe related to the noise,and the changes of WM micro-structure maybe related to the hearing loss caused by noise exposure.In this study,the WM structural abnormalities in ONIHL patients were mainly located in the syndesmosis fibers of the temporooccipito region,which affected the auditory and language pathways,and confirmed that the integrity of the auditory pathways have the abnormal structural connectivity in ONIHL patients,which contributed to further explaining and understanding the mechanism of abnormal brain functional activities in ONIHL.Part 2 Alterations of resting-state functional network connectivity in patients with occupational noise-induced hearing loss:a study based on independent component analysisObjective:To evaluate the resting-state functional network connectivity(FNC)alterations in patients with occupational noise-induced hearing loss(ONIHL),using an independent component analysis(ICA)technique.Method:Patients with ONIHL were the same as part I,including 79 MP group,32 RSP group)and 84 age-and education-matched HC group were recruited.All subjects’ chinical data were collected including age,education level,hearing level,occupation type,the noise exposure time and some scales including Mini-Mental State Examination(MMSE),tinnitus handicap inventory(THI),Hamilton Anxiety Scale(HAMA).Scanning by GE Discovery MR 750 3.0T magnetic resonance equipment underwent the following sequences:the routine brain,inner ear MR examinations,3D-FSPGR brain volume imaging,resting-state functional magnetic resonance imaging(RS-fMRI).Correlation analysis was performed on basic clinical data such as hearing level,noise exposure time and HAMA score(P<0.05).Then,the RS-fMRI data of three groups were processed by ICA technique,For the identified resting state networks(RSNs)were analyzed,and age and education level were added as covariates for analysis of variance;the multiple pairwise comparisons between groups were performed after the post hoc(P<0.001,FDR corrected);Pearson correlation test were used to compare the correlation between the RSNs FNC and noise exposure time,hearing level,HAMA score(P<0.05).Result:The study eventually consisted of 70 MP group,26 RSP group and 72 H group.There were no statistically significant differences in age,years of education,and MMSE score among the three groups,while there was statistically significant differences in HAMA score among the three groups.All patients(MP and RSP)were mainly engaged in drilling and welding(noise environment above 90dB,ineffective protection);there was no statistically significant differences in THI score between the MP and RSP group,but there were statistically significant differences in noise exposure time,hearing level and HAMA score between the MP and RSP group;the noise exposure time was negatively correlated with hearing level and HAMA score,and the THI score was negatively correlated with hearing level.Using ICA technique,29 independent components(ICs)were screened and 24 effective components and 7 RSNs were identified,including dorsal attention network(DAN),visual network(VN),executive control network(ECN),sensorimotor network(SMN),auditory network(AUN),default mode network(DMN),salience network(SN).The three groups had abnormal FNC intra-and inter-RSNs,totaly 19 ICs and 10 RSNs:including intra-RSNs:ECN,DMN interRSNs:AUN-ECN,AUN-VN,AUN-DMN,DAN-DMN,DMN-VN,DMN-ECN,VN-ECN,VN-SN;and there were the FNC of some abnormal RSNs(intra-ECN,AUN-VN,DAN-DMN,VN-SN)significantly positive correlation with HAMA score.Further Post hoc pairwise analysis among three groups:Compared with the HC group,MP group showed increased FNC within ECN,and enhanced FNC within DMN and VN;While compared with the HC group,RSP group showed decreased FNC within ECN and AUN,DMN and VN;there was no significantly changes in FNC were found between the MP group and RSP group;there were no significant correlation between the FNC correlation coefficient of the abnormal RSNs and the hearing level,noise exposure time,and HAMA score.Conclusion:1.Our study showed that different degrees of ONIHL patients have different RSNs FNC changes compared with HC group,which may potentially reflect the reorganization and compensatory activation of the MP for auditory deprivation response,and the adjustment and damage of the brain functional network with the later disease process.2.The correlation analysis between HAMA score and the changes of RSNs FNC suggested that ONIHL patients had abnormal emotional state,and the hearing level and HAMA score were related to the noise exposure time,all these result suggested that exposure to noise environment can lead to changes in a variety of brain functions involving emotion,decision-making,social cognition and psychopathology.Combined with DTI and FNC studies showed that the WM structural abnormalities in ONIHL patients were mainly located in the syndesmosis fibers of the temporooccipito region,which affected the auditory and language pathways;the abnormal RSNs FNC in ONIHL patients were mainly related to the areas related to auditory and language network,which increased FNC in the early stage and decreased FNC to adjust and adapt in the later stage.The structural combined with functional connectivity suggested that ONIHL patients not only have changes in white matter connectivity structure,but also have abnormal brain functional network connectivity,and the abnormal structural connectivity affects the connectivity of specific brain functional network and the abnormal brain functional network connectivity compensates for abnormal structural connectivity.So,it is confirmed that DTI combined with FNC technique can be used to study the neuroimaging abnormalities of ONIHL patients,and from the structural to brain function level evaluating the neuropathophysiological characteristics of ONIHL-related brain injury,which provides theoretical support for the prevention,diagnosis and treatment of ONIHL.