The cause of sudden sensorineural hearing loss (SSNHL) remains unclear and 
therefore it is often considered as idiopathic. Sleep disturbance has been 
linked to SSNHL and circadian rhythm disruption, but the link between circadian 
rhythm disruption and SSNHL has never been investigated.In this study, we 
surveyed the sleep quality of 38 patients with SSNHL using a simple insomnia 
sleep questionnaire. The expression of circadian clock genes in peripheral blood 
(PB) leukocytes from 38 patients with SSNHL and 71 healthy subjects was accessed 
using real-time quantitative reverse transcriptase-polymerase chain reaction and 
validated using immunocytochemical staining.We found that 61.8% of patients with 
SSNHL suffered from insomnia before the insult of hearing loss. Besides, 
significantly decreased expression of PER1, CRY1, CRY2, CLOCK, BMAL1, and CKlε 
was found in PB leukocytes of patients with SSNHL when compared with healthy 
subjects. SSNHL patients with vertigo had significantly lower expression of CRY1 
and CKlε than patients without vertigo symptoms. Our results imply the 
association of sleep disturbance and disrupted circadian rhythm in SSNHL.