A STUDY OF SERUM LIPID PROFILE IN CLINICALLY DIAGNOSED PATIENTS OF SENSORINEURAL HEARING LOSS

Handique Gautom 1 , Das Monigopa 2 and Gogoi Chandrika 3 . 1. GDMO, Department of Biochemistry, Assam Medical College and Hospital, Dibrugarh. 2. Associate Professor, Department of Biochemistry, Assam Medical College and Hospital, Dibrugarh. 3. Demonstrator, Department of Physiology, Assam Medical College and Hospital, Dibrugarh. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

One of the root cause of SNHL which lies in the inner ear (cochlear), its function is greatly influenced by ischaemia since the blood supply of the inner ear is dependent on the end arteriole. Specifically related to the cochlea, the lipid composition, fluidity and stiffness of the outer hair cells internal wall membrane have been shown to be important to its electromotile function and the cochlear amplifier. The lateral wall plasma membrane of the outer hair cells also seems to have less cholesterol than other cells. So, the data suggests that outer hair cell function may be particularly sensitive to dyslipidaemic states.

Objectives:-
This study was undertaken to assess the serum lipid profile in the subjects with SNHL and also to see whether there was any correlation between serum lipid levels and severity of SNHL.

Materials and methods:-
A case control study was carried out among patients with SNHL and healthy subjects of age 18 years and above in the Department of Biochemistry, Assam Medical College and Hospital, Dibrugarh, Assam, for a period of 1 year from June 2014 to July 2015 . The study was conducted on 54 clinically diagnosed SNHL patients attending the Otorhinolaryngology Department of AMCH, Dibrugarh, Assam. Parallel to these cases, 54 healthy subjects of age and sex matched have been selected from normal population and their blood was also examined and this group was marked as control subjects.
In this study the degree of sensorineural hearing loss is classified on the basis of audiogram interpretation as Mild, Moderate, Moderately severe, Severe and Profound with hearing loss range of 26 to 40 db HL, 41 to 55 db HL, 56 to 70 db HL, 71 to 90 db HL and 91+ db HL respectively.
Blood samples were drawn from all the patients after a minimum of 12 hours of fasting. About 5ml of blood was collected from antecubital vein after proper aseptic and antiseptic measures in sterile empty vial (SEV) for estimation of lipid profile. The sample collected was then allowed to clot. After being clotted the sample was allowed to centrifuge at 3000 rpm for 10 minutes. The supernatant clear serum was then pipetted out using micropipettes with disposable tips. The samples were analyzed on the same day.
Following investigations were done to assess the lipid profile level in patients with SNHL and their correlation with various degree of hearing loss.

Results and Observations:-
Age and sex distribution of the subjects are depicted in Figure 1 and Figure 2 respectively. It was found that 30% of the study population belonged to the age group of 18 to 35 years, 34% belonged to 35 to 55 years and 36% belonged to 55 years and above.
On the basis of gender distribution of the study population, it was found that the male subjects were at 54% and females were at 46%.     Table 3 shows that the level of serum total cholesterol, triglyceride, LDL and VLDL are elevated in cases with various degree of SNHL and serum HDL level is elevated in control subjects and the results were found to be highly significant with p < 0.001 and these findings are depicted in Figure 3.

MALE FEMALE
The mean values of serum lipids are also analysed with increase in degree of SNHL (Table 4 & Figure 4).

Discussion:-
Sensorineural hearing loss (SNHL) is a type of hearing loss, or deafness, in which the root cause lies in the inner ear (cochlear), vestibulocochlear nerve (cranial nerve VIII), or central processing centers of the brain. Inner ear function is greatly influenced by ischemia since the blood supply of the inner ear is dependent on the end arteriole 8 . Dyslipidemia is one of the most significant cardiovascular risk factors 3 , and evidence has shown that there is relationship between SNHL and dyslipidemia 4, 5, 6 . There are two primary lipoprotein fractions constituting total serum cholesterol: low-density lipoprotein cholesterol (LDL) and high-density lipoprotein cholesterol (HDL). Serum LDL transports cholesterol from the liver, via the circulatory system, to be deposited in other organs, specifically the arteries and heart. In contrast, HDL transports cholesterol from the organs and tissues back to the liver via the circulatory system. The HDL transport system is thought to be beneficial to the cardiovascular system because it reduces the formation of cholesterol plaques in major arteries. Elevated LDL and decreased HDL characterize coronary artery disease. In addition, an elevated serum triglyceride level is often present, indicating a high level of fat in the bloodstream. However, it is unclear whether dyslipidemia is associated with hearing loss.
So the present study aimed at assessing the serum lipid profile in subjects with sensorineural hearing loss and also to find out the correlation of dyslipidemia with various degrees of sensorineural hearing loss.
In this present study, elevated levels of total cholesterol, triglyceride, LDL and VLDL were found in the cases as compared to that of the controls (p<0.05). Serum HDL level was significantly higher in the control group (<0.05). Among the subjects with various degrees of sensorineural hearing loss, triglyceride and VLDL showed increasing serum levels with the severity of the degree of hearing loss.
Our findings were consistent with the conclusion that dyslipidemia plays a role in the development of sensorineural hearing loss. Despite the fact that lipid parameters were estimated at only one point of time, a significant correlation between dyslipidemia and the various degrees of sensorineural hearing loss was found. This finding is in accordance with studies by Rosen

Conclusion:-
In this study we found that there is an elevated level of serum total cholesterol, triglyceride, LDL and VLDL in cases as compared to the controls. Serum HDL level is significantly higher in the controls. With the severity of the degree of SNHL among the subjects of various degrees of SNHL, triglyceride and VLDL showed increasing serum levels.
The present study reveals a significant correlation of dyslipidemia with SNHL and can be used as an indicator of severity of SNHL. However, the present study had some limitations. One should be very cautious to draw any firm conclusion from this study as it was undertaken for a short span of one year's time with limited number of cases. It was a hospital based case control study; which does not claim to be a study of the population at large of this locality. Therefore, a final conclusion could not be made that there is a causal relationship between dyslipidemia and SNHL. Further study should be focused on cohort study on relationship between dyslipidemia and sensorineural hearing loss.