Patients most commonly present with headaches, severe otalgia, purulent otorrhea and hearing loss and these symptoms correspond to the inflammation of the outer ear. Of note, recurrent MOE may manifest in form of only headaches and otalgia. Otorrhea is not necessarily detected in MOE relapses.

Additional symptoms may be experienced if the infection has already spread to adjacent osseous structures and cranial nerves are compromised. According to a study conducted in 2003, facial nerve palsy should be expected in about 40% of MOE patients whereas only 25% of these patients present with multiple cranial nerve palsies [10]. Facial nerve palsy is associated with altered facial expression, other cranial nerve palsies often result in swallowing problems and voice changes. Pain upon movement of the temporo-mandibular joint may, however be due to local inflammation rather than cranial nerve palsies [11].

During otoscopic examination, inflammation of the external auditory canal and granulation tissue may be observed. The latter is often situated at the osseocartilaginous junction. The tympanic membrane is usually not affected. Signs of otitis media are rarely detected and have been related to skull base osteomyelitis [12].

Because the majority of MOE patients suffers from pre-existing, immunocompromising conditions, symptoms associated with the latter may also be reported. In this line, physicians treating diabetes mellitus patients and individuals suffering from other diseases that weaken the immune system should be aware of the possibility that otitis externa may progress in a malignant form. If otalgia does not subside with adequate treatment, they should be referred to an otolaryngologist.

Ear secretions should be cultured in order to identify the causative pathogen and to establish an antibiogram. This procedure may need to be repeated if approved antibiotics lose effectivity during therapy. It is not uncommon that MOE pathogens change sensibility patterns upon initiation of antibiotic treatment [13].

Granulation tissue samples obtained from the external auditory canal should be examined to rule out neoplastic processes. The latter would not respond to antibiotic and anti-inflammatory treatment.

Furthermore, blood samples need to be drawn to evaluate hemogram and blood biochemistry. Elevated erythrocyte sedimentation rates are characteristic and may later indicate response to treatment as well as development of possible relapses. Blood glucose levels may point at diabetes mellitus, if this condition has not yet been detected in the patient.

Upon tentative diagnosis of MOE, imaging techniques should be applied to assess the extend of tissue inflammation around the ear and to confirm the aforementioned diagnosis [14]. Computed tomography, technetium Tc 99m medronate bone scans and Ga 67 scintigraphy are most commonly used to this end. These techniques often reveal osteomyelitic processes in the temporal bone. Extratemporal osseous structures may be affected in advanced stages of the disease, but such findings have become increasingly rare because adequate antibiotic therapy is nowadays initiated in a timely manner. Of note, for alterations to become recognizable in CT and Tc 99m scans, pathologic processes need to be in advanced states, so early detection of MOE is not possible this way. Moreover, they may not be used to evaluate response to therapy because remineralization takes place delayedly. Because Ga 67 scintigraphy rather detects infectious processes, it may be more valuable for initial diagnosis and follow-up of MOE.

Magnetic resonance imaging may be applied to support the diagnosis of MOE. Retrocondylar fat infiltration is the most commonly detected alteration [9].

MOE treatment involves systemic and local antibiotic therapy, remedy of immunosuppression and, in some cases, surgery.

Antibiotic therapies of MOE are long-term treatments. They should be started even before an antibiogram is available. Because Pseudomonas aeruginosa is the most common causative agents, antibiotics should be selected to this end. If necessary, compounds may be changed if pathogens are found to be resistant against the initially chosen one. Aminoglycosides and β-lactam antibiotics such as penicillins, cephalosporins and carbapenems as well as fluoroquinolones may be used [15]. It may be necessary to combine several antibiotics. Furthermore, patients may initially benefit from antimicrobial dressings. Before local treatment can be initiated, the external auditory canal needs to be thoroughly cleaned and debrided. Necrotic tissue should be removed. Surgery becomes only necessary if bone sequestra or abscesses affecting deeper structures need to be removed [16].

Although it may not be possible in all patients, prognosis significantly improves if the underlying immunocompromising condition can be remedied. Thus, blood glucose levels should be controlled strictly. Appropriate measures need to be taken if pathological conditions other than diabetes mellitus account for immunosuppression. With regards to immunosuppressive medication prescribed to treat comorbidities, potential consequences of reduction or cessation of treatment have to be considered before changing such therapies.

It may be difficult to determine the precise point in time when treatment may be stopped. Due to the high incidence of relapses, therapy should be continued for at least four weeks, possibly longer. Clinical findings such as headaches and otalgia as well as laboratory tests and imaging techniques should be utilized to evaluate the state of recovery.

Prognosis improves if the underlying immunosuppression can be remedied [7]. Cranial nerve palsy, particularly if not limited to the facial nerve (VII), and intracranial complications significantly worsen prognosis. Of note, even though the disease may be cured, facial nerve function may not be completely regained. Thus, facial nerve function should not be used as an indicator for successful treatment.

A recent study has evaluated the prognostic value of magnetic resonance imaging findings and could demonstrate a positive correlation between combined extension patterns and mortality [9].

Relapses are frequent and occur in up to 27% of MOE patients. In order to avoid recurrence, therapy should not be terminated prematurely. Patients remain susceptible for up to one year, so frequent follow-ups should be realized in that time span.

While otitis externa itself is a common disease, progressive forms involving spread of infection to adjacent osseous and soft tissues are rarely observed. The latter is most frequently observed in patients whose immune system has been weakened either by pre-existing pathological conditions such as diabetes mellitus or by immunosuppressive treatment. In this line, chemotherapy has to be considered an immunosuppressive treatment [3].

The most commonly isolated pathogen is Pseudomonas aeruginosa [4]. Infections originate from the external auditory canal and may compromise adjacent structures such as osseous tissue, the base of the skull, cranial nerves and other parts of the brain as well as any other tissue in close proximity to the ear. Due to the severe tissue damage caused by such infections, the disease is also referred to as necrotizing otitis externa.

MOE is more frequently observed in patients suffering from any immunocompromising condition. The majority of MOE patients present with diabetes mellitus, a significant share of patients even shows multiple morbidity [5]. Furthermore, exposure of the ears to water has been associated with an increased risk for MOE. In this context, it is rather unsurprising that MOE incidence is higher in warm, humid climates.

Morbidity and mortality are particularly high among MOE patients whose ear infection compromises cranial nerves or who develop intracranial complications.

With regards to the former, the facial nerve (VII) is the cranial nerve most frequently affected by MOE. Lesions are often located at the stylomastoid foramen. Decades ago, facial nerve paralysis was observed in approximately one out of three MOE patients [6]. However, the incidence of facial nerve paralysis has decreased due to better treatment options and is currently estimated to be around 20% [7].

If disease progress cannot be stopped, the jugular foramen including the glossopharyngeal nerve (IX), vagus nerve (X) and accessory nerve (XI) may be compromised. If the hypoglossal canal is infected, the hypoglossal nerve (XII) may be lesioned. This also applies to the petrous apex and trigeminal nerve (V) and abducens nerve (VI).

Facial nerve lesions usually precede intracranial complications such as meningitis, cerebral venous thrombosis and brain abscess. Such complications often lead to death. However, MOE patients may also die from heart, kidney or liver failure, pneumonia or stroke because of common comorbidities [6]. The overall mortality has been estimated to be about 10 to 20%.

While uncomplicated forms of otitis externa are usually restricted to the external auditory channel, in MOE patients, infection rapidly spreads to the adjacent osseous and soft tissues. Presumably, the fissures of Santorini as well as the bone-cartilage junction of the auditory canal are most easily passed by causative agents such as Pseudomonas aeruginosa [8]. In the course of the disease, osteomyelitis develops and severely compromises the temporal bone. Due to close proximity to cranial nerves, meninges and brain, life-threatening complications may result from the aforementioned osteomyelitic processes.

Nerve damage is further aggravated by neurotoxins released by Pseudomonas aeruginosa .

Because lesions of the external auditory canal greatly facilitate infection, subsequent spread and MOE development, any manipulation that may cause such lesions should be avoided. In this line, susceptible patients should be advised not to use cotton swabs and not to introduce other objects into their ear canal. Otoscopic examinations should be realized with utmost precaution.

Furthermore, exposure to water, particularly to water containing high levels of chloride, should be minimized. Irrigation of the ear should only be carried out when strictly necessary.

Any possible infections of the auditory canal should be treated in a timely manner [17].

Malignant otitis externa (MOE) is a rare but severe condition that may develop from otitis externa upon infection, most commonly with Pseudomonas aeruginosa. This infection affects the external auditory canal, which has often previously been lesioned by the patients themselves or during a medical examination, and rapidly spreads to the surrounding tissues. This process is largely facilitated in patients suffering from a weakened immune system, and while several pathological conditions may involve immunosuppression, diabetes mellitus is the one most frequently associated with MOE.

MOE patients experience severe otalgia, particularly at night, and report drainage of fluids from the affected ear [1]. Otoscopic examination reveals granulation tissue inside the external auditory canals. Both drained fluids and granulation tissue should be analyzed further in order to identify the disease's causative agent and to diagnose MOE.

Because the infection spreads to adjacent osseous and soft tissues, cranial nerves may be compromised and trigger the respective symptoms. Such pathological events as well as other intracranial complications may be evaluated by imaging techniques such as computed tomography and scintigraphy. They significantly worsen the patient's prognosis and may indeed be lethal.

If MOE is diagnosed in immunocompromised patients, this condition should be remedied [2]. Systemic and local drug therapy are required to cure MOE. In some patients, surgery may become necessary.

Malignant otitis externa (MOE) is a rare, life-threatening complication of otitis externa, an inflammation of the outer ear, that involves extensive infection of the external auditory channel and adjacent osseous and soft tissues.

Causes

Infection of the external auditory channel generally results from previously inflicted lesions. Such lesions may be invoked by the patient themselves or by health care providers that realize any manipulation.

The vast majority of otitis externa do not progress to MOE. However, an individual predisposition resulting from a weakened immune system leaves certain patients more susceptible to this complication. For instance, this is the case for people who suffer from diabetes mellitus or receive chemotherapy.

Symptoms

As long as the infection is restricted to the outer ear, headaches, ear pain, purulent discharge from the ear and hearing impairment are the most commonly experienced symptoms. Ear pain is often worse at night and improves during the day.

In MOE, however, infection easily spreads to surrounding tissues. The temporal bone may be affected as well as several cranial nerves that pass this bone. In these cases, nerve palsies may be observed. They often manifest in altered facial expression, difficulties to swallow and to speak.

Additional symptoms depend on the anatomical structures affected in the course of the disease.

Diagnosis

Clinical and otoscopic examination will allow for a tentative diagnosis of MOE. During these exams, samples will be obtained from the external auditory channel for further analysis. This is important to identify the causative agent of the infection and to test its sensibility to a variety of antibiotics.

In order to assess the extend of tissue damage, imaging techniques will be applied. Computed tomography or bone scans will reveal demineralization as well as activation of inflammatory and bone cells.

Treatment

MOE treatment mainly consists in systemic and local antibiotic therapy. It is of utmost importance to continue this therapy even though symptoms may subside earlier because there is a high risk for relapses if treatment is terminated prematurely.

Also, if an underlying immunocompromising disease is detected, this disease, most commonly diabetes mellitus, should be treated. If diabetes mellitus has not been diagnosed in a certain patient and no obvious causes for immunosuppression are registered, they should be thoroughly examined in order to rule out such conditions.

Surgery may be required in cases of severe bone damage.

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