What is a mild hearing loss?
Normal hearing for children is 0-15 dBHL. Minimal hearing loss (MHL) is 15-25 dB HL. Mild hearing loss is 24-40 dB, It doesn’t sound like a big difference but it is. 1/1000 newborns have mild hearing loss (although newborn hearing screening often misses mild hearing loss.) At school age, 3/1000 have MHL.
Why newborn screening misses mild hearing loss
Many hospital use otoacoustic emissions testing as the first screen. Babies you fail are referred for ABR testing. ABR testing will identify babies with moderate or greater hearing loss but not babies with minimal hearing loss. So when babies pass ABR testing they are dismissed from follow-up. Hmmm. We have a problem here.
A study by Johnson et al in Pediatrics 2005, followed up on babies who failed the OAE screen but passed the ABR screen. 4% of 86,634 babies met this criteria. 21 of these babies were found to have permanent hearing loss and 77% had mild hearing loss, with 57% having unilateral hearing loss. Those are big numbers, and it means that there are a lot of babies out there who need assistance who are not receiving it because they “passed” newborn screening.
What about school screening?
Unfortunately, most school screenings also miss mild hearing loss. Testing is often conducted at 25 dB HL and sometimes at a higher level is the room is noisy. So kids with MHL will pass and may be just considered difficult behavior problems. School screening should be performed in a quiet room at 10 dB HL. If not, we will surely miss identifying a significant part of the school population.
What about unilateral hearing loss
Adults with unilateral hearing loss report difficulties with sound localization, hearing in noisy places and feelings of frustration and embarrassment when they misunderstand. Bess and Tharpe in 1986 reported a study in which they looked at 60 children with unilateral hearing loss ages 6-18 yrs. More than half of the children were not identified until 5-6 yrs of age, with 20% being identified at 7-8 yrs and some not until 12 yrs.
Bess and Tharpe found that 38% had failed a grade. A study by Matkin found that 25% failed a grade. Either statistic is startling. It is even more concerning now when children are almost never held back a grade but continue to be promoted even if they are not capable of doing the work.
Bess and Tharp found that 62% of those with academic difficulties had hearing loss in the right ear. The right ear- left brain language connection again rears its ugly head. Teacher Behavior Ratings suggest that children with unilateral hearing loss have problems with social withdrawal, inattention, distractibility and aggression. I am assuming the aggression is a response to frustration.
Unilateral conductive hearing loss
Many people, including physicians and parents, assume that if a hearing loss is conductive it will not affect learning. A study by Kesser et al, 2013 looked at children with aural atresia. None of the 132 children failed a grade but 65% required resource room help and 45% received speech therapy. Because there was an obvious physical deformity, these children were identified at birth so they received services earlier.
In a study by Lieu et al, 2010 children with unilateral hearing loss were compared with siblings. The children with unilateral hearing loss had poorer language comprehension, poorer oral expression. There was no difference between children who had right or left ear HL.
The effects of minimal/mild hearing loss
So what are the statistics?
- Bilateral sensorineural hearing loss 1.0%
- High frequency sensorineural HL 1.4%
- Unilateral sensorineural HL 3%
- TOTAL 5.4%
This is a lot of hearing loss to deal with in a school. Bess et all, 1998 did a study in which they looked at psychoeducational outcomes for children with minimal sensorineural hearing loss. They found that 6th graders had more areas of dysfunction in psycho-emotional areas then peers with significant differences in energy domains. 9th graders had significant differences in areas of stress and behavior.
Technology for MHL and UHL
Depending on the degree of HL, some children may be able to benefit from hearing aids. However, if the hearing loss is severe, binaural interference can be a problem causing a reduction in performance. CROS aids have been tried but have not always been successful. Kenworthy et al, 1990 showed that FM systems provided more benefit than CROS aids in school, but will not provide assistance outside of school. Several recent studies have been looking at cochlear implants for single sided deafness with good results. Other studies have looked at bone anchored hearing aids.
Children with MHL may have a trial with hearing aids. Some will accept them, others will not. ALL children with MHL will benefit from FM systems .
Every child with MHL needs an FM system for school. No question. We know they are at risk for academic failure. We need to identify then and monitor their academic and social development. We can improve their performance. We just need to do it.