The Relationship between the Behavioral Hearing Thresholds and Maximum Bilirubin Levels at Birth in Children with a History of Neonatal Hyperbilirubinemia

Original Article Iranian Journal of Otorhinolaryngology No.3, Vol.25, Serial No.72, June 2013 The Relationship between the Behavioral Hearing Thresholds and Maximum Bilirubin Levels at Birth in Children with a History of Neonatal Hyperbilirubinemia Rasool Panahi1,*Zahra Jafari2, Abdoreza Sheibanizade1, Masoud Salehi3, Abdoreza Esteghamati4, Sara Hasani1 Abstract Introduction: Neonatal hyperbilirubinemia is one of the most important factors affecting the auditory system and can cause sensorineural hearing loss. This study investigated the relationship between behavioral hearing thresholds in children with a history of jaundice and the maximum level of bilirubin concentration in the blood. Materials and Methods: This study was performed on 18 children with a mean age of 5.6 years and with a history of neonatal hyperbilirubinemia. Behavioral hearing thresholds, transient evoked emissions and brainstem evoked responses were evaluated in all children. Results: Six children (33.3%) had normal hearing thresholds and the remaining (66.7%) had some degree of hearing loss. There was no significant relationship (r=-0.28, P=0.09) between the mean total bilirubin levels and behavioral hearing thresholds in all samples. A transient evoked emission was seen only in children with normal hearing thresholds however in eight cases brainstem evoked responses had not detected. Conclusion: Increased blood levels of bilirubin at the neonatal period were potentially one of the causes of hearing loss. There was a lack of a direct relationship between neonatal bilirubin levels and the average hearing thresholds which emphasizes on the necessity of monitoring the various amounts of bilirubin levels. Keywords: Behavioral, Hearing threshold, Hearing loss, Hyperbilirubinemia, Neonatal. Received date: 29 Aug 2012 Accepted date: 28 Nov 2012 1 Department of Audiology, Faculty of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran. Department of Basic Sciences in Rehabilitation, Faculty of Rehabilitation, Rehabilitation Research Center, Tehran University of Medical Sciences, Tehran, Iran. 3 Department of Biostatistics, Faculty of Management and Medical Information, University of Medical Sciences, Tehran, Iran. 4 Children's Hospital, martyr Akbar-Abadi, Tehran University of Medical Sciences, Tehran, Iran. *Corresponding Author: Department of Basic Sciences in Rehabilitation, Faculty of Rehabilitation, Tehran University of Medical Sciences, Nezam Alley, ShahidShahnazari St., Mother Sq., Mirdamad Blvd., Tehran, Iran. Tel: +982122228051-2, Fax: +982122220946, E-mail: z_ . 2 127 Panahi R, et al Introduction High bilirubin level at birth has been considered as one of the most important factors affecting the auditory system. Although this disease does not have thoughtful consequences in most infants, in the absence of appropriate treatment, high levels of blood serum bilirubin can result in acute encephalopathy and brain damage (1,2). When red blood cells are broken down, unconjugated bilirubin enters into the plasma. Normally, this type of bilirubin molecules link together by liver enzymes and make conjugated bilirubin that the body is able to excrete. However, if the bilirubin does not convert to a conjugated mode, it accumulates in plasma and its concentration increases. With increasing levels of serum bilirubin, the substance passes through the blood brain barrier and enters the central nervous system. Kernicterus is a neurological syndrome that is due to unconjugated bilirubin deposits in brain cells and nuclei (3). Due to the involvement of vestibular nerve, oculomotor nerve, cerebellum and cerebral basal ganglia, patients with kernicterus develop symptoms such as movement disorders, impaired eye movements and hearing loss. The only clinical sign of kernicterus may be permanent sensorineural hearing loss (4,5). Jaundice in the first day following the birth is always pathologic. Likewise, if the maximum level of bilirubin in term neonate exceeds beyond 13 mg/dL, it is considered pathologic (6). Severe hyperbilirubinemia is defined as serum bilirubin levels above 17 mg/dL (7). It seems that auditory brainstem nuclei including the cochlear nuclei, inferior colliculus and superior olivary complex are the most vulnerable parts of the auditory system against high bilirubin concentrations. Damage to these structures can lead to Sensor-Neural Hearing Loss (SNHL) (3,8). Studies that reviewed audiological findings in children with a history of neonatal hyperbilirubinemia have primarily used electrophysiological and non-behavioral tests such as auditory brainstem response (ABR). For instance, the study of Jiang et al on infants with a history of neonatal hyperbilirubinemia revealed that the threshold of ABR response recorded in these infants was significantly increased (9). In the study of Nickisch and colleagues in 2008 on two groups of children with a history of neonatal hyperbilirubinemia, it was reported that 87% of children in the group with serum bilirubin levels greater than 20 mg/dL and 13% of children in the group with serum bilirubin levels between 12-19 mg/dL suffered from particular hearing impairment (10). Evidence suggests that lower levels of bilirubin may cause minor encephalopathy that known as bilirubin- induced neurological dysfunction (BIND). In this case, the hearing impairment has been reported alone and without any other signs of kernicterus (8). The relationship between peak serum bilirubin levels and behavioral hearing thresholds has not well-defined yet furthermore there is not enough evidence in this field. Considering the results of these studies and assuming that different degrees of neonatal hyperbilirubinemia can cause different degrees of hearing impairment, our study investigated the behavioral hearing thresholds in children with a history of neonatal jaundice and reported the frequency of hearing impairment. This study also addressed the relationship between the average hearing thresholds and level of serum bilirubin. Materials and Methods This study was performed from January to June 2012 at the audiology department of faculty of rehabilitation in Tehran University of Medical Sciences. Our study was performed on 18 children aged 2.4 to 11 years (mean 5.6±2.5 years) and with a history of neonatal hyperbilirubinemia. Of these, 10 were girls (55.6%) and 8 (44.4%) were boys. Additional information regarding 128 Iranian Journal of Otorhinolaryngology No.3, Vol.25, Serial No.72, June 2013 Relationship Between Maximum Bilirubin Level and Hearing Thresholds in Neonatal Hyperbilirubinemia the children is summarized in Table 1. Blood bilirubin levels at birth for each child were determined according to the medical record. In the inclusion criteria, a history of phototherapy or exchange transfusion, negative family history of hearing loss, no history of respiratory distress, no history of head trauma, epilepsy and ototoxic medications and negative history of oth (...truncated)