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Thursday, 25 August 2011

Hearing loss after radiotherapy for NPC

Total hearing loss is uncommon. Reduced hearing loss either on one side of ear or on both sides can happen during and after chemotherapy and radiotherapy for NPC.

Causes of hearing loss DURING concurrent Cisplastin chemotherapy and radiotherapy is due to Cisplastin chemotherapy side effect that can cause high frequency hearing loss and tinnitus (ringing in the ear). If these symptoms happen, the patient need to alert the doctor. Most of the tinnitus and high frequently will resolve once the chemotherapy has been stopped. Some patients have to discontinue the chemotherapy early if the hearing loss is severe. Persistent hearing loss can happen in some patients when the chemotherapy was continued and not stopped despite the onset of hearing loss. It is very unusual for radiotherapy to cause hearing loss DURING radiotherapy. Radiotherapy however can cause a late onset hearing impairment.

Causes of hearing loss AFTER completion of treatment from 3 months onward to lifelong could be due to several factors:

1) After effect of Cisplastin chemotherapy that has persisted since during chemotherapy. This usually improved with time over the next few months but in a small number of patients, persistent high frequency hearing loss will continue for life.

2) After effect of radiotherapy damage to the cochlear (inner ear) that maintain the sensory-neural conduction of hearing from ear to the brain. In IMRT radiotherapy, the radiation oncology doctor will try to spare the cochlears on both sides and avoid giving high dose radiotherapy to the cochlear. While this is in most cases possible, in patients with a large NPC cancer, this cancer can be very near the cochlear and hence cannot be spared. Fortunately, we have 2 ears and in this case, one side of the cochlear will receive a higher dose of radiotherapy to gain maximum cancer control on the side where the cancer is nearest to cochlear while sparing the other side. Damage to cochlear results in a long term hearing loss and the hearing loss is gradual and may take 6 months to life long before patient notice. It will not be apparent immediately on completion of radiotherapy.

3) The radiotherapy to the NPC will cause some radiation to mid and inner ear. Inflammation at these areas can cause fluids to built up and affect the ear drum function. Furthermore the Eustachian tube which connects the nose and the ear can be blocked leading to nasal blockage and ear ache. These areas are also susceptible to bacterial infection causing otitis. In severe causes, the ear drum may burst when the swelling builds too high and the ear pain will reduced, but the hearing will be impaired with a burst ear drum. In recurrent fluid built up, the ENT doctor will consider inserting a grommet which is a small tube at the ear drum level to drain the fluid out. When the fluid is drained and the fluid reduced over the next few months, the grommet can be removed. The ENT doctor commonly will also prescribe ear drop antibiotics and/or oral antibiotics to treat ear infections and frequently contribute to the fluid build up.

4) Ear wax can build up in the external ear causing hearing impairment and pain and the easy solution is to use some olive oil to loosen the ear wax and for it to come out gradually over the next few days or for ear syringing or a small vacuum suction tube can be inserted to suck up the wax under a ENT doctor consultation. The hearing will be back to normal immediately if it is the ear wax that is the cause of the hearing impairment.

In summary, total hearing loss is uncommon, but a certain degree of hearing impairment  is a well known side effect of after treatment of NPC and could be caused by chemotherapy, radiotherapy, inflammation or infection combination. Alerting the ENT doctor early to look into the ear with a otoscope (shining a light into the ear),  can usually find a cause. Further specialist investigations include a full hearing test to check the loss of hearing frequencies or a CT scan to look into the anatomical structure of the cochlea, Eustachian tube and the nose. In the worse case scenario, patients may need to wear a hearing aid for life. A hearing aid may work in most cases, but in certain group of patients, hearing aid will not improve the hearing back to a normal functional degree.

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