By Mr M. Hawthorne FRCS Consultant ENT Surgeon
It is extremely rare for a diagnosis of Ehlers-Danlos Syndrome to be made with hearing impairment as the sole abnormality. Most ENT surgeons will usually be told by the patient that they have Ehlers-Danlos Syndrome, but few are aware of the effects of this condition on the middle ear.
The conducting mechanism of the middle ear is the primary site of abnormality in patients with Ehlers-Danlos Syndrome. As most people are aware sound hits the tympanic membrane and is conducted across the air-filled middle ear to the inner ear by three tiny bones known as the malleus, incus and stapes (hammer, anvil and stirrup bones). Hypermobility of the joints between these bones means that sound is not conducted effectively across the middle ear cleft. In addition to that the ligaments which are attached to these bones may also be affected by the condition causing an overall laxity of the conducting mechanism. This will present as hearing impairment of gradual onset.
Significant hearing impairment due to Ehlers-Danlos Syndrome is rare. In my experience patients usually become aware of a hearing impairment in middle life. Paradoxically, some patients are aware that they hear better in places of background noise. This is because people tend to raise their voices in areas of background noise such as among a group of friends on a Saturday evening in a public house.
The eardrum will appear normal on inspection and tests will reveal that the inner ear is functioning normally but that there is a conductive hearing loss due to loss of energy across the inner ear conducting mechanism.
Important Differential Diagnosis
There is a much more common inherited disorder of hearing known as Otosclerosis which can be easily confused with the type of hearing impairment seen in Ehlers-Danlos Syndrome. It is vitally important for the ear surgeon to be able to differentiate between the two. Like Ehlers-Danlos Syndrome, Otosclerosis also runs in families, the eardrums are normal, and there is a hearing loss due to an abnormality of sound conduction across the middle ear.
Otosclerosis may be effectively treated by an operation known as stapedectomy. However, an attempt to undertake a stapedectomy on a patient suffering from Ehlers-Danlos Syndrome could easily end in disaster with a total loss of hearing and a severe disruption of balance.
In Otosclerosis the joint between the stapes bone and the inner ear is stiff whereas in Ehlers-Danlos Syndrome the joint is likely to be hypermobile. Surgical interference with the stapes in circumstances with a hypermobile stapes / inner ear joint could lead to dislocation of this joint with disastrous results.
The safe and effective way of treating the mild to moderate hearing impairment which occurs in Ehlers-Danlos Syndrome is with a hearing aid. If necessary additional aids can be provided for the home such as a door bell which causes the kitchen or sitting room lights to flash, a television aid, a vibrating alarm clock.