Audiologists have not determined exactly what causes auditory processing disorder (APD), although there has been some consensus that there are two primary types:
- Acquired APD: The child was born with normal auditory function, but at some point the hearing system was disrupted causing lack of development in the auditory cortex.
- Hereditary APD: People are born with an impaired auditory cortex, thus causing APD.
In the case of acquired APD, some insult to the brain disrupted the stimulation of the auditory cortex. This in essence reduced the development of the auditory processing.
Excessive ear infections (otitis media) is the most issues for what causes auditory processing disorder. When a child has an ear infection, fluid remains in the ear for 45 days after the infection is cleared. The child is essentially hearing ‘under water,’ which creates muffled hearing. This in turn reduces the amplification of what is hear, and the result is the auditory cortex is under stimulation. So the auditory processing system is wired properly, but it has been under stimulated, thus creating auditory processing disorder.
Other causes of acquired APD can include a head injury (even ‘just’ a concussion), certain antibiotics, reaction to the DTaP vaccine, or excessive high fever from illness. 45% of people with head injury will have some form of auditory processing difficulty, so the issue is a common one.
The good news is acquired APD can be helped with therapies. In the case of under stimulation, listening therapies and auditory exercises can be used to help the auditory system develop. In the case of head injury, listening therapies can also help, but therapies to heal the brain like neurofeedback or hyperbaric oxygen therapy can often do more to resolve the issues.
With hereditary APD, it can be difficult to know what causes auditory processing disorder. The person is born with an auditory system that is hardwired in such a way that auditory processing does not develop normally. Often there are several family members who display the same symptoms, and it is common for a parent to finally understand their own hearing challenges when their child is diagnosed. There is no DNA test available to help determine if the APD is hereditary, only standard APD testing of several family members can determine that.
Sometimes the hereditary component of APD is not that the auditory cortex is mis-wired, but that the family is predisposed to have excessive ear infections. The ear infections then cause acquired APD. So family history is important to help determine if the APD is hereditary or acquired.
Hereditary APD does not always respond to therapies. Sometimes therapies aimed at improving the auditory processing can improve the symptoms of APD, so it is worth trying. But just realize that the improvement may not be as much as a person who has acquired APD. Accommodations for APD are the best way to help someone who has hereditary APD.
How to know if it is Acquired or Hereditary?
Sometimes you cannot pinpoint what causes auditory processing disorder. A history of ear infections or brain trauma that could have caused the APD, but sometimes you won’t know that information. There may also be no family members to indicate a hereditary history. In this case you should consider treating the APD as acquired since an illness or medication may have caused it without you realizing it. If therapies do not improve the APD, then you may consider that it is hereditary and APD accommodations will be the best approach to managing it.