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Online EHDI Case 6 (Part 3 with Answers)

Online EHDI Case 6: Late-Onset Bilateral Progressive Sensorineural Hearing Loss

Part 3

Tommy returns for his 9 months old check up. He continues to grow and develop well. Soon after his diagnosis, he started to receive early intervention services and was fitted with hearing aids. He has now accepted his hearing aids and wears them during all waking hours. A repeat ABR had been completed a couple months ago which confirmed the severity of the loss without any more progression. The family is pleased with the observation that they are seeing at home and the way Tommy consistently responds to sounds when he has his hearing aids on.

He was recently seen by his audiologist again and behavioral testing (Visual Reinforcement Audiometry) was obtained reliably and revealed similar thresholds compared to his last ABR.

The medical work up is also well underway and medical results are back. The MRI did not reveal any anomalies, but genetic tests revealed a mutation in the GJB2 gene, encoding the connexin 26 (Cx26) protein at the 13q12 location.

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1. What are your thoughts now?

 For hearing losses associated with this particular mutation of the Cx26:

   • Males and females are equally affected;
   • Congenital mild to profound sensorineural hearing loss (more commonly severe to profound);
   • Usually non-progressive, but may be progressive (in this case, it is progressive);
   • Autosomal recessive, meaning that each parent is unaffected but is a carrier of a single mutation;
   • On average, 25% of the couple’s children are expected to inherit both copies of the mutation and be affected;
   • No other comorbidities.

If Tommy’s genetic tests had come back negative, his hearing loss could still be from an unidentified genetic etiology. Other potential causes may be an undetected asymptomatic congenital CMV infection.

It has been reported that 90-95% of infants with congenital CMV infection will have no clinically apparent symptoms (asymptomatic) at birth (Mccollister, Sabo EHDI, 2005- link to
http://www.infanthearing.org/meeting/ehdi2005/presentations/02--McCollister_EHDI2005.ppt).

Most congenital CMV infections go unnoticed in the nursery since the majority of infected newborns will have no clinically apparent disease at birth. Both symptomatic and asymptomatic infants may later develop outcomes which could include sensorineural hearing loss (SNHL), impaired vision, and mental retardation. About 25% of hearing loss in children by four years of age is likely CMV-related hearing loss. These numbers suggest that CMV is the leading non-genetic cause of hearing loss in children in the United States.

Unfortunately, the fact that congenital CMV infection can only be confirmed in the newborn period has made it difficult to estimate the proportion of SNHL that is attributable to congenital CMV infection in childhood populations.

Current standard practice does not allow us to determine if a newborn has asymptomatic CMV infection. Therefore, this group of children at risk for progressive hearing loss currently goes unidentified. Because viral shedding decreases over time, it is difficult, if not impossible to make the diagnosis once the child presents with parental concerns. Studies are ongoing to determine the feasibility of performing universal newborn screening for asymptomatic CMV. Should this type of screening be found to be efficacious, we may be able to more effectively monitor the status of this group of high risk children. Currently, however, the most effective tests for diagnosing asymptomatic CMV are not known and there are many unanswered questions related to how to manage a newborn that may be diagnosed with asymptomatic CMV.

In summary, the following statements can be made related CMV and other causes of late onset or progressive hearing loss:
   • Approximately 33 to 50% of SNHL due to congenital CMV infection is late onset loss.
   • The fact that over 90% of congenital CMV infection is asymptomatic at birth and that CMV can only be confirmed in the newborn period has made it difficult to estimate the proportion of SNHL that is attributable to congenital CMV infection in childhood populations.
   • In addition to CMV and genetic conditions, other conditions may put a child at risk for progressive hearing loss. Such conditions include inner ear anomalies, viral or bacterial meningitis, mumps and other viral infections that cause a high fever or central sequelae, head trauma with skull fracture; chemotherapeutic agents.

2. What are the main teaching points of this case? 

• The importance of being sensitive to parental/caregivers concerns. As mentioned in the JCIH 2007 Position Statement, caregiver concerns regarding hearing; speech; language or developmental delay is a risk indicator, which should not be ignored.
• Some childhood hearing losses have a later onset and will not be identified through screening methods. UNHS is only a screening tool and could miss a mild or minimal hearing loss. Thus, vigilance towards ALL babies, even those who pass their UNHS should receive continual developmental monitoring. JCIH 2007 is a great resource to refer to when in doubt about guidelines, referrals, risk factors.
• Risk factors that represent greater risk indicators for late-onset hearing loss include viral or bacterial meningitis, mumps and other viral infections that cause a high fever or central sequelae, head trauma with skull fracture; chemotherapeutic agents.

3. How can you, as a primary care provider, monitor for late onset hearing loss?

• Monitor infants and young children by listening to the family; performing surveillance and developmental monitoring- revised auditory skills development and developmental milestones at well-child visits.
• Immediate referral for audiological evaluation is warranted if parents express concerns about a child’s hearing responsiveness or speech and language development.
• For children under 3 years of age, typical in-office hearing screening methods are not effective (limited attention span; too many distractions; untrained staff) and a referral to a pediatric audiologist is recommended.
• All children with identified risk factors for late-onset hearing loss should receive a comprehensive audiological assessment as soon as behavioral testing can be completed (even if they passed the UNHS and there are no parental concerns).

 

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