Physicians and scientists from The Ohio State University, Nationwide Children’s Hospital and the University of North Carolina at Chapel Hill have joined forces to improve care for pediatric cochlear implant users who have cochlear nerve deficiency (CND).
Supported by a $2.02 million R01 grant from the National Institutes of Health (NIH), the team aims to better understand how children with small or absent cochlear nerves encode and process electrical signals generated by cochlear implants. They hope to develop the first set of evidence-based guidelines for programming cochlear implant processors in children with CND.
Cochlear implant users need customized programming
Although cochlear implantation has been used to treat children with CND for nearly 20 years, most of these patients don’t meet important speech and language milestones – especially compared to children with normal-sized cochlear nerves.
Ordinarily, cochlear implants help restore hearing by capturing sound signals and converting them to electrical impulses. These impulses stimulate the cochlear nerve, which carries auditory information from the inner ear to the brain.
Following cochlear implantation, audiologists program the external speech processor to pick up soft and loud sounds. Over time, patients learn to interpret these sounds and hopefully develop speech and language skills.
“Audiologists typically try their best to fine-tune the settings for many children based on their assertions that they can hear different sounds coming through the device,” says Shuman He, MD, PhD, associate professor in Ohio State’s Department of Otolaryngology – Head and Neck Surgery and the study’s principal investigator. “However, more than half of children with CND have concurrent neurological issues that prevent them from providing reliable behavioral responses. As a result, it is clinically challenging or impossible to optimize programming settings for these patients.”
Exploring a link between damaged nerves and auditory processing
Dr. He says there is zero clinical evidence to support the selection of programming parameters, and limited understanding of how deficient cochlear nerves respond to electrical stimulation.
“Without knowing the lowest level these children can hear, or the highest level they can tolerate, we rely on a combined ‘one-size-fits-all’ and ‘try-and-see’ approach and hope it works,” she adds.
Over the next five years, Dr. He and her team plan to enroll 164 pediatric cochlear implant users. Half will have CND, and half will have normal-sized cochlear nerves, as measured by high-resolution MRI.
First, they’ll test how well each child’s cochlear nerve responds to the electrical stimulation sent by their cochlear implant at different locations along the cochlea. Then they’ll compare both groups to evaluate the differences in how their nerves responded and, subsequently, how that affected auditory processing at the brain level.
“Our previous research found that the likelihood of measuring cochlear nerve neural responses in children with CND reduced as the stimulating electrode site moved from the base of the apex to the cochlea,” Dr. He says. “This unique response-deterioration pattern is not observed in children with normal-sized cochlear nerves.”
An urgent need to create objective clinical tools
As candidacy criteria continue to evolve, more patients with CND may become eligible for cochlear implantation. Among children with bilateral, severe to profound hearing loss, the prevalence rate of CND is around 5%. But in children with single-side deafness, the prevalence can be up to 50%.
“Although current guidelines limit cochlear implantation to children with profound bilateral hearing loss, we may eventually implant children with hearing loss in just one ear,” Dr. He explains. “Once we begin putting cochlear implants in children with single-side deafness, we’ll face significant challenges in how to program around half of them.”
Addressing hearing impairment across the lifespan
The joint cochlear implant program at Ohio State and Nationwide Children’s is one of the busiest in the country, performing an average of 80 adult and 80 pediatric surgeries annually. This collaboration also fosters innovative research that benefits patients of all ages.
In addition to Dr. He’s new study, other scientific projects underway or in the works include:
- Investigating the underlying neurophysiological mechanisms of speech perception deficits in older cochlear implant users, to better understand why users who are 65 years or older typically show poorer speech perception performance than younger adult users
- Developing electrophysiologic technology that evaluates inner ear function and minimizes intracochlear damage, in real time, during pediatric and adult cochlear implant surgeries
- Exploring how deafness caused by different genetic mutations affects neurological function and cochlear implant outcomes