Pompe Disease and Hearing
Hearing loss is a very common for infants with Pompe disease. It may also affect some people who develop Pompe disease later in life. Here is information about how hearing works, how Pompe disease can cause problems with hearing, and how doctors diagnose and treat hearing loss in these patients.
How does hearing work?
Hearing is a complex process that involves multiple parts of the ear. The ear is divided up into three major sections: the outer, middle, and inner ear. The pinna (the outer, visible portion of the ear) collects sound and funnels it to the ear canal. These two structures make up the outer ear.
As the sound reaches the end of the ear canal, it causes vibrations in the tympanic membrane or eardrum. A series of three small bones of the middle ear, called the ossicles, transfer these vibrations from the eardrum to another membrane called the oval window. This membrane connects to an organ in the inner ear called the cochlea.
The cochlea is full of fluid that flows back and forth with vibrations on the oval window. The fluid’s movement activates a special sense organ inside the cochlea, called the organ of Corti. This structure contains special nerve cells called hair cells, arranged to pick up sounds of different frequencies along the cochlea. The hair cells convert the movement of the fluid into nerve signals. These nerve signals then travel along the auditory nerve to the brain, where they are interpreted as sounds.
What types of hearing problems are common?
Research has shown that most children with classic infantile-onset Pompe disease (IOPD) experience mild to severe hearing loss. This loss is usually apparent shortly after birth. Patients tend to have sensorineural hearing loss (problems involving the cochlea and auditory nerve). However, conductive hearing loss (a problem with the outer or middle ear) can also be present.
Hearing loss of some degree can also affect adults with late-onset Pompe disease, but at a prevalence rate not higher than the general population. One small study in 11 adult patients did find a slightly higher rate of mild hearing loss in these people than is generally reported.
How does Pompe disease cause hearing problems?
The exact mechanism of hearing loss in Pompe patients people is not clear. Research suggests that the buildup of glycogen in parts of the cochlea is responsible for sensorineural hearing loss. This buildup may begin during prenatal development. A study, which initially found sensorineural hearing loss in all four infants with Pompe disease, further investigated its cause in a mouse model of Pompe disease. Results showed that the mice had glycogen storage in the hair cells and other nerve cells of the cochlea, leading to hearing problems.
Infants with IOPD often have weakness in the facial muscles. One group of researchers proposed that conductive hearing loss may be due to weakness in the tensor veli palatini muscle, which opens the Eustachian tube (the canal that connects the middle ear to the upper throat and the back of the nasal cavity to maintain the correct pressure in the middle ear). Weakness in this muscle could cause a drop in pressure in the middle ear, making it harder for the vibrations to pass through the small bones of the middle ear.
In the study in adult patients, problems in the workings of the stapedius muscle, a muscle that controls vibrations in the middle ear, was also apparent in up to 36% of these patients.
How do doctors diagnose them?
Doctors can use a number of different methods to detect hearing problems. They can use a technique called pure tone audiometry to assess hearing loss in both adults and children. Using headphones, they play a number of pure tones at a single frequency or pitch, like a beep, at different intensities (degrees of loudness) until the patient cannot hear the sound. Later, they compare the level at which the patient can detect each frequency against a reference level for an average patient of the same age.
Since infants cannot easily indicate whether they heard a tone or not, doctors often use a different technique with babies, called a brainstem auditory evoked response. They again play pure tones or clicks through headphones. At the same time, electrodes placed on the back of the head and behind the earlobes record whether or not the brain received signals from these tones. Changes in the shape of the signal recorded can help doctors estimate the degree of hearing loss. It can also help in distinguishing problems with the auditory nerve.
Once they detect hearing loss, they can use other tests to determine where the problems may be occurring. In otoacoustic emissions testing, a small microphone placed inside the ear “listens” for sounds that the hair cells produce in response to sounds. Doctors can use this test to detect hearing problems in the cochlea of the inner ear.
To look for issues with the middle ear, they use impedance audiometry. This test checks for problems with the tympanic membrane, pressure inside the middle ear, and reflexes of the muscles in the middle ear.
How do doctors treat them?
Enzyme replacement therapy, an effective treatment for Pompe patients, does not seem to lessen hearing loss. The only treatment options available for patients are hearing aids or cochlear implants, depending on the part of the ear that is dysfunctional.
It is important to diagnose hearing loss early in infants. A baby given hearing aids that might help early in life is more likely to learn to speak normally. Speech therapy can also help children with hearing problems.
Last updated: Jan. 19, 2021
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