Otitis externa

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Otitis externa is inflammation of the outer ear canal[1] It usually presents as one or more of the complaints of an earache, a persistent itch in the ear, a runny ear, deafness of the affected ear, or red and swollen skin in or around the ear canal or external ear. It is most often an acute condition, almost always an infection of the skin and subcutaneous tissue of the canal, which may spread to involve the skin surrounding the ear, the face and neck, the local lymph glands and the salivary glands. Uncomplicated recovery is the norm, but in diabetics and immunocompromised persons rapid spread is potentially dangerous and requires prompt treatment. Chronic otitis externa affects fewer persons, is often a manifestation of a general inflammatory skin disease (for instance soborrheic dermatitis), and may be defined as signs or symptoms of otitis externa that lasts for more than four months, or occurring more than four times per year. The body of this article concerns acute otitis externa, the chronic disease will be described separately in its own section. When the causes of the illness are understood, then it is clear that most cases of otitis externa could be prevented by proper preventative measures.

Anatomy and physiology pertinent to understanding otitis externa

The external ear canal serves to protect the middle and inner ear from injury, while providing an air passage for the conduction of sound, together with the pinna amplifying and improving directional localisation of sound. Being a blind-ending tube, it is vulnerable to blockage and infection. Certain characteristics reduce the risk of infection occurring. The skin lining the external ear shows a unique pattern of growth, growing in a sideways direction, moving as a sheet of tissue from the eardrum end to the outer opening. This mass movement of the epithelial layer of cells carries with it cellular and foreign debris which may collect on the skin of the inner part to where it may be easily picked off at the outer opening – a self-cleaning mechanism which is foiled when an object like an earbud is pushed from the outside inwards. The skin is covered by a layer of cerumen (wax) produced by the skin glands of the outer third of the canal. This wax is a barrier to infection of the skin by virtue of its water repellancy, relatively acidic pH of 6.9, and its content of lyzosyme.[2] Hairs occur on the skin of the outer third, serving to prevent entry of foreign material to the inner two thirds.

Anatomically,the skin of the inner two-thirds of the ear canal is extremely thin, and closely overlies the bone. The lack of underlying fat and supporting tissue makes this skin vulnerable to scratches, tears and cracking. At the junction of the bony and cartilaginous parts, the adult ear canal makes a turn forwards and downwards, forming a bend where larger bits of material can get stuck. The outer third has thicker skin, supported by cartilage and fatty tissue and containing hair follicles and skin glands. It is therefore less commonly the site of origin of an otitis externa.

Incidence and pathology

Most cases of early acute otitis externa heal with simple measures such as stopping swimming, with or without eardrops such as 2% vinegar, or 70% alcohol (or a mixture of the two) as preventative and therapeutic treatment. These cases seldom come to the attention of health services, which has the consequence that estimates of the incidence of otitis externa are unreliable.

Acute otitis externa is common, with an incidence of approximately 13 per 1000 patients in general practice in the Netherlands[3] and Britain,[4] and 4 per 1000 in the United States.[5] A study of more than 40,000 cases in 30,000 persons over a year in British general practices showed a prevalence in females of 1.3%, and males 1.16%, the highest yearly prevalence being in persons 25 and 75 years of age. More than 20% had more than one episode.[4] As skin infections go, and for the volume of the infected tissue, otitis externa has a significant morbidity (negative effect on general health). In a swimming-associated outbreak of 94 cases, a third suffered a median of four days of loss of normal activities, while slightly more than one fifth took to their beds for a median of three days.[6]

For acute otitis externa, a common initiating event is water carried into the external ear canal, and in contact with the thin skin for prolonged periods. This leads to maceration of the skin lining the canal. Moist macerated skin is a good culture medium for the organisms carried in with infected water. The association of otitis externa with swimming or diving, especially in contaminated water, has given rise to the common name of “swimmer’s ear” or “diver’s ear”. Repeated contact with water increases the risk of maceration and infection by reducing the protective layer of cerumen, while decreasing the acidity of the skin in the outer ear. On the other hand, excessive wax may promote trapping of water in the canal. Humid weather and warm temperatures increase the likelihood of skin maceration, and the incidence of acute otitis media. The second important cause of initial infection is mechanical injury to the skin by objects such as hearing aids and ear plugs, or “instruments” persons use to clean out their ears.[7] The offending instrument may be anything from a fingernail to a matchstick to a cotton earbud (this may of course be equally risky for causing an ear drum perforation). Apart from damage due to attempts at cleaning the canal, the skin may be scratched in an attempt to alleviate the itch of mild otitis externa, or the perceived blockage of the canal, leading to exacerbation of the condition. Less commonly, conditions such as eczema or psoriasis disrupt the continuity of the skin, allowing invasion of pathogenic bacteria (a case of an acute infection following chronic inflammation).

Whatever the initiating event, the bacteria multiply and cause an acute infection and inflammation of the skin and subcutaneous tissue (cellulitis). The ear canal swells shut and the ear develops a discharge. At this stage the person may complain of hearing loss in the affected ear, as well as tinnitus (a persistent ringing in the ear) which is caused by the occluded ear canal. If the infection is not contained, it may in severe cases spread along the subcutaneous tissue, causing a cellulitis of the neck and the side of the face. Local lymph glands become acutely inflamed, and the parotid salivary gland enlarged and tender (so-called diffuse external otitis[8]). In such cases, differentiation from malignant otitis externa (see the next paragraph) purely on grounds of the examination may be difficult.

Acute or chronic otitis externa may progress to affect the cartilage of the ear (chondritis), or the bones surrounding the ear canal (osteomyelitis). The latter tends to be progressive and difficult to cure, with a risk of infection spreading through the bone to other parts of the skull and even the central nervous system. This malignant or necrotising form of otitis externa is more common in diabetics or immune compromised persons, and requires aggressive treatment, both surgical and medical.[9]

For a few weeks after an episode of acute otitis externa the outer ear is susceptible to becoming infected more easily than normal. The skin itself is thinned and lacks a normal outer protective keratin layer, while wax production decreases markedly, even after all infection has disappeared. Therefore repeat exposure to the precipitating circumstances is likely to cause another bout of the disease.

The organisms implicated in otitis externa are most commonly opportunistic pathogens, that is, organisms that do not cause disease in healthy tissue, but can infect tissue where the immunity is reduced. Macerated skin, scratches and loss of cerumen represent such local loss of immunity, while diabetes, AIDS and chemotherapy are systemic causes. Pseudomonas aeruginosa is found in up to 50% of cases, other bacterial infections (Staphylococcus epidermides, Staphylococcus aureus, and Streptococcus pyogenes) account for 40%, and fungi about 10%.[10][11][12]

Symptoms

Ear discomfort is the usual symptom of otitis externa. This may be an itch and mild pain, or, in advanced cases, severe pain requiring strong analgesics. When not just minor, pain is disproportionate to the volume of inflamed tissue, because the tissue is confined to a small volume and impinges on bony boundaries, so that increased local pressure and irritation of periosteum occurs early on. Since the pinna and the tragus is connected to the cartilage of the outer third of the ear, and that to the skin, movement of these structures causes pain from distortion of the inflamed skin. This extreme sensitivity to movement is generally not found in uncomplicated otitis media, the other common cause of earache.

A discharge from the ear commonly occurs, but is usually not the primary complaint. It can vary from a mild watery consistency and colour, to thick, yellow or white, to a bloody purulent discharge.

Redness and swelling can usually be seen in the ear canal. The swelling may obscure the canal completely, so that the ear feels blocked up and deaf, and be a source of tinnitus. The outer ear and surrounding tissue may show these symptoms and signs of inflammation, depending on the spread of the infection. The signs of a diffuse otitis externa can be confused with malignant otitis externa.[8]

Bacterial otitis externa is associated more severe local symptoms and morbidity than other causes. The person with acute bacterial otitis externa may feel ill, complain of headache, and develop a moderate fever, usually less than 38.3°C. More severe illness would prompt the examining person to look for complications.

Some predisposing factors, and associated preventative measures

Anyone can develop oitits externa, and mild forms may go undiagnosed in persons who experience simply an itchy ear for a while. There are, however certain activities, circumstances and medical conditions where the risk for the disease increases. All of the risks apply also to immunocompromised persons, the chronically ill and diabetics – groups also at increased risk for the complications of otitis externa. Such persons should take particular care to avoid activities which predispose to otitis externa, or be particular about preventative measures when such conditions are unavoidable.

Where the person is engaged in activities that entail prolonged exposure of the external ear canal to water, the protective cerumen on the skin in the canal may be gradually washed away, leaving the skin unprotected. Loose surface keratin can now absorb moisture, becoming macerated and effectively a culture medium for bacteria. Since the pH of the ear increases at the same time, there is no protection against such growth. Swimmers and divers are clearly at risk, and regular swimming remains the most significant risk factor for acute otitis externa, with fresh water being more of a problem than sea water or chlorinated pools.[13][14][15] Water which is considered safe by the standards for fecal coliform contamination may contain high numbers of organisms that may cause infection of a damaged external ear canal, but the precise correlation is not clear.[16] Spells of hot weather, with high humidity and excessive sweating present a similarly increased risk of developing acute otitis externa. Preventing water getting into the ears would logically be the best preventative measure for those who love swimming. This can be achieved by the use of a well-fitting bathing cap, or properly fitted ear plugs, but hard or ill-fitting ear plugs may exacerbate the problem. It is unfortunately not known how effective this “logical” measure is in preventing the disease. Measures used after swimming include thorough drying of the ears and the use of acidifying ear drops. Drop containing alcohol, and Burow’s solution (5% aluminium subacetate solution) both have an astringent action, but may be irritating, especially if the skin is not entirely normal. Drying the ears using an ordinary hair dryer set on its lowest heat is effective, while battery powered hot air ear dryers are marketed. Following an attack of ititis externa, the use of acidic ear drops before and after swimming is often recommended, for at least three weeks, and in the long term if the infection tends to recur.

Direct trauma to the skin of the inner two thirds of the external ear canal is easily inflicted, especially near the junction with the outer third, where the canal makes a change of direction and the skin becomes thin and tightly applied to the underlying bone. The habit of personally cleaning one’s ears is more dangerous than beneficial, and while kitchen matches, the classroom protractors, and the beautician’s beautiful nails are clearly dangerous instruments, the soft tips of cotton ear buds are deceptively harmless, and one of the very common causes of hurting the soft skin lining the bony canal – as well as the ear drum. Ironically, damage is not infrequently done by “beneficial” acts, such as inserting a hearing aid earpiece or wearing ear plugs in an attempt to prevent noise-related hearing damage or prevent water from getting into the ear canal. Foreign bodies that lodge in the external ear are an important cause in young children, and in mentally retarded persons. The danger here is not always the presence of the object, but do-it-yourself or kindly third party efforts to remove the object. The same applies to adults, where an enormous variety of objects such as insects, seeds or bit of wood cuttings can get stuck in the outer ear. If these are not removed atraumatically under direct vision, then the scene may be set for damage to the outer and middle ear, including an episode of acute otitis externa a day or two later.

Health workers are not blameless with respect to damaging the external ear canal. A professional person who removes wax or any other object from an ear using sharp instruments under inadequate vision runs the risk of causing injury. If that is not diagnosed and treated to prevent infection, the situation is no better than if the patient had done the scratching himself. The incorrect use of an otoscope is another entirely iatrogenic cause. Even syringing of the ears should be considered a predisposing condition for otitis externa, by washing away protective wax and altering the pH in the ear canal. Many health workers recommend the prophylactic use of acidic ear drops for a few days following such a procedure.

The last group of risk factors is to a large extent beyond the direct control of a person. This is where a general dermatological condition has affected the skin of the ear. In many of these cases the person would be suffering from a chronic, low grade inflammation of the outer ear canal. The itch that this causes may lead to scratching activities which set off the acute otitis externa, or an acute exacerbation of the primary disease may disrupt the integrity of the skin. Conditions which can be included here are acne, atopic dermatitis, contact dermatitis, eczema, lupus erythematosus, psoriasis, and seborrheic dermatitis.[17] A person should be aware that allergic contact dermatitis may be confined to only the skin of the outer ear, so that the diagnosis may be missed because there are no symptoms or signs of dermatitis elsewhere. Immune-mediated otitis can occur in response to the metals contained in earrings or studs, chemicals in cosmetics and hair care products, solvents used in the plastics used to make hearing aids, and medications in ear drops (especially antibiotics). Apart from the allergic risk of antibiotic ear drops, alteration of the skin bacteria may lead to fungal infections, usually after prolonged use of these drops. Persisting with the antibiotic treatment only worsens the condition.

Diagnosis

When a person presents with complaints of ear discomfort, itching, pain, a discharge, or a deaf or ringing ear, the doctor would take a history of how and when the symptoms started, how they have developed and what contributory factors there may be – this would include previous ear problems, treatments, other illnesses, accidents and injuries, as well as daily activities and sport. During the examination, the patient may be surprised that the doctor does not look only at the sore ear, but there are good reasons for this. A general assessment for signs of systemic illness, including the temperature, pulse rate, and signs of toxicity, would be done. If a severe headache and fever is present, the signs of meningitis would be sought. The neck, face, jaw, sinuses, nose, mouth and throat would be examined for accompanying problems, specifically for pain on movement or palpation, discharges, colour changes, swelling, and tenderness of skin and glands, all of which may indicate spread of the infection. The unaffected ear may often be examined before the one that is causing the problem, which may cause the patient to doubt whether the doctor had heard the complaint correctly. While the comment that “it’s not that ear” is entirely appropriate, the healthy ear may be examined first to assess what is normal for the patient, and to make her more comfortable with an examination which may turn out to hurt somewhat on the affected side.

On the affected side, the presence and the nature of any ear discharge would be noted, as well as the colour and texture of the skin outside the ear. Swelling of the external ear structures can be seen without resorting to any painful contact. If the pinna is not inflamed, the examiner may pull gently on it, to see whether that causes the ear canal to hurt. Alternatively, light pressure may be applied to the tragus (the triangular bit of skin-covered cartilage that sticks out in front of the external ear canal, opposite the pinna). This pain on movement of the external ear structures is virtually diagnostic of otitis externa, but it does not mean that this is the complete diagnosis, that is, the person may be suffering from more than just outer ear infection.

The redness and swelling of the external ear canal may be obvious on just looking at the ear, and an examination with an otoscope would be attempted to visualise the precise nature of the material in the ear canal (for instance a foreign body or fungal growth), ascertain the patency of the canal, and attempt to determine the appearance of the ear drum – specifically if it shows a perforation. Depending on the facilities available, the examiner may use an ordinary hand-held otoscope, or may need to make use of an examining microscope. It would often be necessary to remove debris and pus from the canal before anything can be seen, and for this a low suction catheter is preferably used, so that further damage to the inflamed skin and bleeding may be prevented as much as possible. If a proper examination cannot be done without causing intolerable pain, and the diagnosis was reasonably certain, then treatment would be started anyway. An appointment for a more complete examination would usually be scheduled for when the pain and swelling has subsided enough to enable effective otoscopy. At the follow-up examination the canal would once more be cleaned, and another attempt made to see what the ear drum looks like. Such follow-up examination may need to be repeated. Flushing the ear, as is done for clearing ear wax, should never be done unless the examiner is certain that the ear drum is intact. Flushing may also further hurt the already irritated skin.

In the presence of a severely swollen canal, ear drops may not be able to reach the infected tissue. In such cases the doctor may place a thin cotton lint or wick past the obstructed area, to carry medication to the whole length of the ear canal. This serves also as a path for drainage of remaining inflammatory fluid.

In the adult patient a urine or blood test for diabetes would be part of a routine investigation, but otherwise special investigations such as laboratory studies and x-rays are not necessary for an uncomplicated otitis externa; the diagnosis and treatment is based on the history and the physical findings. On the other hand, severe infections with systemic toxicity would require appropriate investigation to identify underlying causes and diagnose dangerous infections.

Treatment

The goals of treatment would be to treat the pain, cure the acute infection, and advise the patient (or responsible persons) on how to prevent recurrences. Treatment starts when the ear is being examined for the first time, by removing as much debris and exudate as can comfortably be done. At this stage a wick may be inserted to facilitate the penetration of ear drops. Local medication would mostly be inserted at the same time. Where debris cannot be removed satisfactorily, and especially where the ear drum cannot be seen, the ear examination may need to be repeated until a satisfactory response has been observed. In the majority of cases the patient would be given oral medication for pain, and ear drops to treat the ear infection. Systemic antibiotics may sometimes be necessary, as when infection has spread outside of the range of penetration of ear drops, or the patient is at a high risk for the disease spreading (for instance with chemotherapy and depressed white cell counts).

Pain

There is a paucity of scientific information on the best treatments for the pain of otitis externa, which is somewhat strange when one considers that is what most patients complain about when they ask for treatment. Fortunately, it can be assumed with reasonable certainty that recommendations for conditions such as a tooth abscess or severe cellulitis elsewhere would be effective. Local heat is frequently helpful in reducing pain, and may be applied using a warmed water bottle. There is a definite risk of causing skin burns, since the pain from thermal skin damage may be masked by the pain of the otitis, so that care should be taken to test the temperature on an area of unaffected skin such as the fore-arm. The object used may of course become contaminated with bacteria; it should be thoroughly cleaned after every use. Oral medications for pain would include paracetamol (acetaminophen), anti-inflammatory drugs (aspirin and equivalents), and opiates (morphine-like drugs, such as codeine), the type and dosage depending on the age of the person, concomitant illnesses, severity of the pain, and the preferences of the patient and doctor. Combinations of different classes of analgesics generally give the best response with minimal side-effects. The duration of pain can be shortened by local cortisone-containing drops, as well as by effective anti-infective treatment.

Anti-infective treatment

The use of antibiotic ear drops is the preferred first line of treatment when infection is not wide-spread (in wide-spread cases topical antibiotics would not reach all of the infected tissue), and the patient does not have an underlying disease that represents a risk for serious complications.[18] In some cases, acetic acid alone is adequate.[19] The specific preparation used is determined by what infecting agent is suspected, by patient sensitivity or allergy, and by the presence or absence of a perforated ear drum. Since tissue concentrations of active drug in the ear canal may reach levels three orders of magnitude greater than what can be achieved by systemic use, the problem of potential ototoxicity – specifically damage to the auditory nerve by aminoglycoside antibiotics – is a concern. Whatever antibiotic is used, the treatment should be followed conscientiously.[20] Equally important, the drops must be able to reach the infected tissue. If the ear canal is partially closed, the use of a wick facilitates penetration of medication. Keeping the affected ear upwards for a while following insertion of the drops, and gently pressing on the tragus in a pumping action, improves the penetration of drops. In children, the application by another person is recommended. The ear drops both combat infection and wash out debris from the ear canal, so that sufficient drops may be used to run out freely after application – absorbent paper or cotton wool on the ear would soak up excess liquid when the person gets up. It may be noted here that the large database of cases analysed by Rowlands et al[4] shows that persons who receive corticosteroid only ear drops recover as well as those who receive antibiotic and steroid drops, but details of the degree of infection is not known (that is, the doctors may have used steroids only for milder cases). Drying and anti-infective agents such as Burow’s solution seem to be effective in clearing up even complicated local infections, but discomfort on application may limit the use thereof.[21] Steroids would not be used for suspected fungal infections.

Systemic antibiotics, whether by mouth or by injection, may be deemed necessary when extensive spread or a local complication has occurred, the patient shows signs of systemic toxicity from the infection, or the patient is at increased risk of systemic infection due to decreased immunity and there is some doubt whether local drops would reach all of the infected tissue.

The symptoms should resolve completely within a week. If reduction in symptoms and signs does not begin within 2 days of starting treatment, culture of the ear fluid should be undertaken to establish the sensitivity of the offending organism, and one should search for local complications or unsuspected persistent aggravating or predisposing factors. Together with a lack of improvement, the presence of a perforated ear drum and suspicion of bony spread of the infection (persistent severe pain and headache) may prompt a referral to an ear nose and throat surgeon.

Preventative measures

For those that do consult a health professional, advice on preventative measures should be part of the treatment. Education of the public who may not have suffered from the disease is desirable, particularly including parents and sportsmen (for instance at schools, and swimming or diving clubs).

The preventative measures described in the section on predisposing factors apply to persons who have had a previous episode of otitis externa or not. The most important of these measures are to dry the ears after swimming or diving, and to avoid any activities that may disrupt the continuity of the skin in the external ear canal (“picking and pushing is perforating”). Particular care should be taken where the person has suffered an episode of acute otitis externa in the preceding three weeks. Ear plugs on their own may be insufficient to prevent episodes of external otitis. In humid weather, and in persons who sweat a lot, the use of astringent drops may be superior to acidification alone.

It is the responsibility of health authorities to check public swimming places for bacterial load, but private pools and saunas represent an unmonitored risk. Persons should take note of any known cases of otitis externa in those who have used the facility recently.

Awareness of the potential of jewellery and chemical substances for causing local immune-mediated inflammation may help solve difficult cases and prevent recurrence.

Self treatment

It is not recommended that a person self-treat otitis externa, but persons with chronic or frequently repeating conditions often do this anyway. It should be noted that problems such as an ear drum perforation or a cholesteatoma may have developed since last the ear was examined, especially if there is an underlying problem that causes repeated episodes of otitis. This may make self treatment dangerous, with the potential for causing damage to the middle ear. Any symptoms of local spreading or systemic illness such as headache and fever would argue strongly against attempting self-treatment. Should a person decide to ignore this advice and self-treat with a solution such as 2% acetic acid or Burow's, then the potential for harm caused by inadequate treatment may be reduced if the rule is followed that drops are used therapeutically at least four times a day, and for at least three days after all symptoms have resolved. This is quite different from the preventative use of drops, where one application every day or two after swimming may have been prescribed. Furthermore, where a person has accepted self-responsibility for this condition, the attention of a health worker should be sought as soon as possible when symptoms do not begin to resolve within two days, or progress in spite of treatment, or any new symptoms appear, or symptoms persist for a week. In geographical locations where a doctor may not be available, a community nursing sister or pharmacist or the expedition medic may be qualified to at least look into the ear to exclude major perpetuating factors such as a foreign body, may be able to clean the ear, and may be able to supply appropriate antibiotics.

Non-prescription remedies should be used only for prevention, not therapeutically, unless the treatment has been advised by a qualified health worker.

Complicated otitis externa

The main complications of acute external otitis are spread of the infection to other soft tissues, persistent chronic infection, and the development of skull bone infection (termed malignant or necrotizing otitis externa, or osteitis of the base of the skull). Spread to soft tissue of the head and neck is managed as for any infection of those tissues. The development of chronic otitis externa may follow an episode of the acute disease, or its onset may be insidious, either from a localised allergic dermatitis or as part of a general inflammatory dermatitis.

Chronic otitis externa

Persistent or chronic otitis externa is usually not due to infection, but rather to chronic skin conditions, which includes local skin allergies, especially contact dermatitis. In the person suffering from atopic dermatitis, such unexpected activities as eating the foods which contain unknown allergens may be responsible for the condition. While inadequate treatment of infection may lead to the persistence of symptoms of inflammation, it may be the antibiotic drops themselves causing a cell-mediated allergic reaction in the ear – a case of an infectious dermatitis going on to become a chronic allergic dermatitis. A chronic ear discharge and itching may follow the placement of middle ear ventilation tubes (“grommets”), and the cause is likely only to be diagnosed by a thorough ear examination.

Treatment may be best managed by input from both an ear nose and throat surgeon, and a dermatologist. An accurate diagnosis is essential for the best outcome, and a number of special tests may be required before such a diagnosis is established. The treatment would vary widely, from surgery to standard preventative treatment as for acute external otitis, and the outcome depends mainly on the treatability of the cause.

Osteomyelitis of the base of the skull

This highly dangerous condition is known by three names: necrotising otitis externa[22] occurs when acute otitis externa spreads to cause osteomyelitis of the base of the skull,[23] which is also called malignant otitis externa.[24] “Necrotising” refers to the death of affected tissue, “malignant” refers to the bad behaviour and poor outcome of the infection, “osteitis of the base of the skull” points out which tissue is infected where in the body. Osteomyelitis of the skull base is dangerous not only because it destroys bone, but because, in addition to affecting the full thickness of the bones and their periosteum, it involves the underlying dura, the major vessels and cranial nerves of the base of the skull, and the surrounding soft tissue. The group of persons who were originally described as being at risk for developing this complication of otitis externa are older diabetics, but it is now apparent that all persons who are immuno-compromised (chemotherapy, leukemia, HIV infection) are at risk, though the disease has slightly different characteristics in persons with AIDS.[25] Radiation therapy to the bones of the skull is also associated with the disease. The symptoms and signs include severe, continuous pain felt deep inside the ear, and headache over the temple area. The pain seems out of proportion to the observed changes in the external ear canal and varies in the course of a day, being more severe at night. There may be a purulent, possibly foul smelling discharge from the ear. The patient may have difficulty swallowing or speaking, and possibly paralysis of one side of the face. The area directly below the ear canal is tender. When the external ear canal is examined, the ear drum is usually seen to be intact. Bare bone, areas where the external ear canal is denuded of skin, was reported in all of six cases seen in an Indian hospital over 10 years.[26] A growth of red, friable granulation tissue, located at the junction of the inner bony canal and the outer cartilaginous part, in the lower part (floor) of the external ear canal, is considered to be diagnostic of the condition. There may be demonstrable loss of function of various cranial nerves, while disturbance of mental function may indicate that the brain is affected. In spite of the severity of the condition, fever is not usually present.[27] The offending organism is almost always pseudomonas aeruginosa. Twenty years ago the mortality was still reported as 53%,[28] but improved antibiotics have reduced that to approximately 10%. Diseases that this condition need to be differentiated from include a number of cancers, shingles of the ear, and Paget’s disease of bone. There are two explanations offered for why diabetics are so susceptible to osteomyelitis of the base of the skull. The first is that the occlusion of small blood vessels found in diabetics predisposes them to necrosis of bone, while at the same time decreasing delivery of antibiotic drugs to the affected tissue. The second is the decreased effectiveness of leukocytes found in diabetics. Both these reasons are equally valid for explaining the tendency of diabetics to develop infections and gangrene right at the other end of their bodies, in the feet. The statistic that 50% of cases of malignant otitis externa in diabetics have a recent history of having a traumatic ear wash out, suggests that these patients had been suffering from a non-specific discomfort of the ear for a while before the osteitis started (hence the washout), and that it was aggravated or spread by injury incurred during the lavage.[27]

The course of the untreated disease is a steady progression of symptoms and signs eventually leading to death. There is a progressive involvement of the cranial nerves. While loss of movement on one side of the face (cranial nerve VII) is not a fatal condition, loss of swallowing and laryngeal reflexes (Cranial nerves V (trigeminal), VII (facial), X (vagus), XI (accessory), and XII (hypoglossal)) may lead to aspiration into the lungs of secretions, food or regurgitated stomach content. Such events may lead to pneumonia. Following the cranial nerve palsies, meningitis, brain abscesses, and thromboses of the cerebral arteries, veins and sinuses can occur, which may be rapidly fatal. Given the age and co-morbid conditions that these diabetic patients may suffer from, the person is at risk for intercurrent acute illness of the lungs, heart and kidneys, not directly related to the disease in their head. [24]

When the diagnosis is suspected, the special investigations which may be done include laboratory tests for the underlying causative diseases, assessment of the hematological and immune response to the infection, and baseline measurements of the function of vital organs such as the kidneys, which are necessary for planning and following up treatment and the course of the disease. Testing for the type of organism and its sensitivity to different antibiotics is essential, while a biopsy of the granulation tissue in the ear canal is needed to examine for possible cancer. Radio-isotope imaging studies (“scintiscans”) that can detect bone resorption and deposition and spread of inflammation – depending on the isotope technique used – are valuable to confirm the diagnosis, as well as to determine the response to treatment. Computer tomographic x-ray studies (“CT scans”) can show bone destruction and alterations in density, as well as alterations in soft tissues such as abscesses. They are not very sensitive to early changes, detecting osteomyelitis only after 30% of the bone density has been lost. Magnetic resonance imaging (“MRI scans”) usually shows soft tissue changes more clearly than CT, but visualises bone changes poorly. Neither one of the last two techniques is suitable for determining the response to treatment on a weekly or monthly basis. The person suspected of having osteomyelitis of the skull base may therefore be subjected to a battery of tests for diagnosis, and a different set of tests for follow-up at different intervals.

Treatment is aimed at eliminating the primary source for the infection (external ear canal), treating any underlying systemic disease effectively, managing the person’s pain, distress and fear, eliminating the bacteria from the bone and soft tissue which has been invaded, treating the complications of nerve paralysis and effects of infection on the nervous system, and planning for preventative measures in the future. The treatment of each one of these aims follows standard recommendations, and a description of all the possible therapies is outside the scope of this article. Aggressive medical management is the present recommendation for acute disease, with surgery rarely being necessary except to treat abscesses and remove sequestered bone.[29] Accurate control of blood glucose levels, aggressive treatment of the otitis externa, and adequate doses of appropriate antibiotics for a suitable length of time can cure up to 90% of cases. Frequent bacterial cultures is invaluable for selecting the antibiotic treatment, since sensitivities of the organism may change during therapy. Hyperbaric oxygen therapy is recommended by some, but has not been proven to improve the outcome of the disease. The duration of therapy is determined by blood tests and by isotope scans which can show the elimination of infection and inflammation, treatment being continued for a week after tests have returned to normal. Duration of treatment varies from 4-17 weeks, and follow-up isotope scans and blood tests have to be done to eliminate reactivation of disease.[30]

References

  1. The reader should note that inflammation and infection are not synonymous.
  2. Tsikoudas A, Jasser P, England RJ. Are topical antibiotics necessary in the management of otitis externa? Clin Otolaryngol Allied Sci 2002;27:260-2.
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