Hearing loss has long been associated with diabetes mellitus. Microangiopat
hy, associated with thickening of the basement membranes of small vessels,
has been implicated as a major source of multiple system organ disease.
Objective This study was designed to evaluate changes in basement membrane
thickness in the inner ear of laboratory animals suffering from non-insulin
-dependent diabetes mellitus (NIDDM) with, and without, exposure to moderat
e intensity noise exposure in an attempt to extrapolate the same disease pr
ocess in humans.
Design Spontaneously hypertensive-corpulent non-insulin-dependent rats (SHR
/N-cp) were selected as a genetic model for the above study. Both lean and
obese rats were used in this study. A genetically similar control group of
animals (LA/N-cp) were used as controls. These animals express both the lea
n and obese phenotypes, but they lack the NIDDM gene. Forty-eight animals i
n each group were sacrificed at the end of the study. The cochleas were dis
sected and fixed. The basement membrane of the stria vascularis was examine
d using transmission electron microscopy.
Setting This study was a laboratory-based, standard animal study.
Main outcome This study was designed to show microangiography of the inner
ear as related to NIDDM with, and without, obesity and noise exposure.
Results/Conclusions NIDDM alone does not cause statistically significant ba
sement membrane thickening; however, NIDDM in combination with obesity and/
or noise exposure did show significant thickening and the combination of al
l three showed the greatest thickening. NIDDM appeared to be the greatest c
ontributing factor.