Otitis externa, a common ear infection, refers to an infection of the ear canal, or the tube leading from the outside opening of the ear in toward the eardrum. The external ear canal is a tube approximately 1 in (2.5 cm) in length. It runs from the outside opening of the ear to the start of the middle ear,designated by the ear drum or tympanic membrane. The canal is partly cartilage and partly bone. In early childhood, the first two-thirds of the canal ismade of cartilage, and the last one-third is made of bone. By late childhood,and lasting throughout all of adulthood, this proportion is reversed. The lining of the ear canal is skin, which is attached directly to the covering ofthe bone. Glands within the skin of the canal produce a waxy substance calledcerumen (popularly called earwax). Cerumen is designed to protect the ear canal, repel water, and keep the ear canal too acidic to allow bacteria to grow.
Bacteria, fungi, and viruses have all been implicated in causing ear infections called otitis externa. The most common cause of otitis externa is bacterial infection. Occasionally, fungi may cause otitis externa, and two types of viruses have also been identified as causes.
Otitis externa occurs most often in the summer months, when people are frequenting swimming pools and lakes. Continually exposing the ear canal to moisture may cause significant loss of cerumen. The delicate skin of the ear canal,unprotected by cerumen, retains moisture and becomes irritated. Without cerumen, the ear canal stops being appropriately acidic, which allows bacteria tomultiply.
Other conditions predisposing to otitis externa include the use of cotton swabs to clean the ear canals. This pushes cerumen and normal skin debris back into the ear canal, instead of allowing the ear canal's normal cleaning mechanism to work, which would ordinarily move accumulations of cerumen and debrisout of the ear. Also, putting other items into the ear can scratch the canal,making it more susceptible to infection.
The first symptom of otitis externa is often itching of the ear canal. Eventually, the ear begins to feel extremely painful. Any touch, movement, or pressure on the outside structure of the ear (auricle) may cause quite severe pain. If the canal is sufficiently swollen, hearing may become muffled. The canalmay appear swollen and red, and there may be evidence of greenish-yellow pus.
In severe cases, otitis externa may have an accompanying fever. Often, this indicates that the outside ear structure (auricle) has become infected as well. It will become red and swollen, and there may be enlarged and tender lymphnodes in front of, or behind, the auricle.
A serious and life-threatening otitis externa is called malignant otitis externa. This is an infection which most commonly affects patients who have diabetes, especially the elderly. It can also occur in other patients who have weakened immune systems. In malignant otitis externa, a patient has usually hadminor symptoms of otitis externa for some months, with pain and drainage. Thecausative bacteria is usually Pseudomonas aeruginosa. In malignant otitis externa, this bacteria spreads from the external canal into all of the nearby tissues, including the bones of the skull. Swelling and destruction ofthese tissues may lead to damage of certain nerves, resulting in spasms of the jaw muscles or paralysis of the facial muscles. Other, more severe, complications of this very destructive infection include meningitis (swelling and infection of the coverings of the spinal cord and brain), brain infection, or brain abscess (the development of a pocket of infection with pus).
Diagnosis of uncomplicated otitis externa is usually quite simple. The symptoms alone, of ear pain worsened by any touch to the auricle, are characteristic. Attempts to examine the ear canal will usually reveal redness and swelling. It may be impossible (due to pain and swelling) to see much of the ear canal, but this inability itself is diagnostic.
If there is any confusion about the types of organisms causing otitis externa, the canal can be gently swabbed to obtain a specimen. The organisms presentin the specimen can then be cultured (allowed to multiply) in a laboratory,and then viewed under a microscope to allow identification.
If the rare disease malignant otitis externa is suspected, computed tomography scans (CT scans) or magnetic resonance imaging (MRI) scans will be performed to determine how widely the infection has spread within bone and tissue. Aswab of the external canal will not necessarily reveal the actual causative organism, so some other tissue sample (biopsy) will need to be obtained. The CT or MRI will help the practitioner decide where the most severe focusof infection is located, in order to guide the choice of a biopsy site.
Antibiotics which can be applied directly to the skin of the ear canal (topical antibiotics) are usually excellent for treatment of otitis externa. Theseare often combined in a preparation which includes a steroid medication. Thesteroid helps cut down on the inflammation and swelling within the ear canal.Some practitioners prefer to insert a cotton wick into the ear canal, leaving it there for about 48 hours. The medications are applied directly to the wick, enough times per day to allow the wick to remain continuously saturated.After the wick is removed, the medications are then put directly into the earcanal three to four times each day.
In malignant otitis externa, antibiotics will almost always need to be giventhrough a needle in the vein (intravenously or IV). If the CT or MRI scan reveals that the infection has spread extensively, these IV antibiotics will need to be continued for six to eight weeks. If the infection is in an earlier stage, two weeks of IV antibiotics can be followed by six weeks of antibioticsby mouth.
The prognosis is excellent for otitis externa. It is usually easily treated,although it may tend to recur in certain susceptible individuals. Left untreated, malignant otitis externa may spread sufficiently to cause death.
Keeping the ear dry is an important aspect of prevention of otitis externa. Several drops of a mixture of alcohol and acetic acid can be put into the earcanal after swimming to insure that it dries adequately.
The most serious complications of malignant otitis externa can be avoided bycareful attention to early symptoms of ear pain and drainage from the ear canal. Patients with conditions that put them at higher risk for this infection(diabetes, conditions which weaken the immune system) should always report new symptoms immediately.