Researchers are not certain exactly what causes APD, although they have found a strong correlation between many factors. In professional circles there has been a lot of discussion about two possible origins of APD:
- Acquired APD: Something happens to the hearing system that impairs proper development or injures an otherwise healthy auditory cortex.
- Hereditary APD: People are born with APD
Acquired Auditory Processing Disorder
With acquired APD, there is usually some trauma to the brain or some health issue with the ears that reduces stimulation of the auditory cortex.
The most common cause of early childhood APD is excessive ear infections (otitis media), which often causes glue ear in the middle ear. This causes reduced amplification of sound to the inner ear, resulting in reduced stimulation of the auditory cortex. In this case the auditory system does not develop properly, but often responds very well to therapies. Note that not all children with excessive ear infections will develop APD, but those diagnosed with APD often have a history of ear infections.
Other causes of acquired APD can include head injury, high fever, certain antibiotics, allergic reaction to the DPT/DTaP vaccine. In these cases the auditory system is damaged through trauma.
Hereditary Auditory Processing Disorder
With hereditary APD the auditory system in the brain is hardwired in a way that impairs auditory processing. Usually when there is a hereditary component, there will be several family members who have similar symptoms. It is common for a parent to diagnose their own communication difficulties when seeking help for their child. There is no genetic test available to identify hereditary APD.
Note there can also be a hereditary tendency to acquire APD, in which case it can sometimes be confusing if it hereditary or acquired. For example, there may be a hereditary tendency to get excessive ear infections which then leads to APD.
The only way to know if the APD is acquired or hereditary is to have a full evaluation done by a qualified audiologist.