Infectious diseases of external ear

Infectious diseases of the external ear include a variety of infection-induced inflammatory disorders of the auricle and the external acoustic meatus, also known as the external auditory canal (EAC). The pathological process usually affects the skin and the underlying tissues (the hair follicles, the fatty layer of the subcutaneous tissue, the cartilage, and the perichondrium), but may also spread to deeper structures. 

Classification

1. Auricular infections: 

• Auricular erysipelas;
• Auricular perichondritis;
• Herpetic infection of auricle;
• Auricular abscess.

2. Otitis externa:

• Furuncle of external auditory canal (infiltration and abscess stages);
• Bacterial diffuse otitis externa;
• Otomycosis (Aspergillus niger);
• Otomycosis (Candida albicans);
• Herpetic infection of external auditory canal;
• Malignant (necrotizing) otitis externa;
• Keratosis obturans.

Etiology

External ear infections can be caused by various microorganisms (bacteria, viruses, fungi, etc.) or their combinations (mixed infections). Staphylococci (S. aureus, S. epidermidis, and S. saprophyticus ), streptococci (group A β-hemolytic Streptococcus), and Escherichia coli belong to the most common bacterial pathogens , whereas Pseudomonas aeruginosa, Proteus mirabilis, and Klebsiella account for the most severe cases. Herpetic infections are caused by herpes simplex virus type 1 (HSV-1) and varicella-zoster virus (VZV; human herpesvirus 3), while otomycosis is primarily associated with Candida albicans and Aspergillus niger. 

It is important to note that a disease can only develop if there are certain predisposing factors. These include damage to the skin and/or maceration, a disturbance of local pH, insufficient earwax production, decreased physiological body reactivity, as well as a concomitant extraorgan pathology (e.g., metabolic and immunodeficiency disorders).

Anatomic Pathology

Auricular erysipelas (cellulitis) is an acute bacterial infection of the skin and the fatty layer of the subcutaneous tissue in the auricular region, including the earlobe. It can be identified by a clear line of demarcation between involved and uninvolved tissue. The affected area is characterized by erythema and significant swelling, causing the skin to appear stretched and shiny. The inflammation often extends beyond the auricle and continues to the neck, temporal, and buccal regions. Moreover, regional lymph nodes may be involved, resulting in lymphadenitis. In some cases, hemorrhagic and serous-filled blisters may appear, which subsequently burst and become covered with crusts.

Auricular perichondritis is a diffuse inflammation of the tissue covering the cartilage of the external ear (perichondrium). The skin of the auricle is also affected, while the earlobe remains intact. Typically, this condition arises when an infectious pathogen enters the system through damaged skin or suppuration of an undrained auricular hematoma or seroma develops. In some cases, perichondritis can be a complication of otitis externa. The most common symptoms are local hyperemia and heterogeneous swelling of the auricle. Notably, the inflammatory process does not spread beyond the auricle and does not involve the earlobe.

Auricular abscess is a localized collection of pus between the perichondrium and the cartilage of the auricle. It looks like a cavity filled with purulent fluid surrounded by inflamed auricular tissues. The skin around an abscess typically appears red, swollen, and stretched. Fluctuation can also be observed. There may be a variety of causes for an auricular abscess. These include the lack or absence of proper treatment for perichondinitis, an infection of an auricular hematoma, and immunodeficiency disorders.

Herpetic infections of the external ear are a group of recurrent skin diseases caused by herpes viruses type 1 (HSV-1) and 3 (VZV). After the initial infection, the herpes virus travels to the nerve ganglia, where it remains inactive for some time. This is called the latent (dormant) stage. The virus reactivates and spreads along the nerve fibers in response to a number of internal and external factors, including a weakened immune system, stress, UV radiation, exacerbation of chronic conditions, etc. This leads to an outbreak (exacerbation stage), which is characterized by typical skin changes. The affected area becomes erythematous and swollen, with numerous small blisters on it. In 2–3 days, these vesicles rupture and crust over. Subsequently, the crusts fall off when the healing is complete. If scratched, a bacterial infection may develop, thus prolonging and complicating the course of the disease.

In HSV-1 infection, vesicles can spread randomly all over the skin. VZV, on the other hand, gives rise to two clinically distinct forms of disease. Chickenpox represents a primary infection that prevails in children. The other form of the disease is herpes zoster, also known as shingles, which develops when the latent virus reactivates. It is characterized by the involvement of the dermatome, an area of skin innervated by a particular nerve. VZV typically affects the facial nerve, which can lead to its paresis or paralysis. The virus may also attack the geniculate ganglion of the facial nerve, resulting in Ramsay Hunt syndrome (Herpes zoster oticus). Rarely, the infection may involve the trigeminal or vestibulocochlear nerves. Since the infectious process spreads along the facial nerve, it can affect not only the skin of the auricle and EAC but also the tympanic membrane. In severe cases, the central nervous system may be involved, leading to meningitis and encephalitis. Immunocompromised patients are at risk of developing a generalized herpetic infection because the virus can spread throughout the body. It is usually a recurrent disease that is extremely difficult to treat.

Furuncle of the EAC (sometimes known as localized otitis externa) is an infectious inflammation of the hair follicle and surrounding tissues (the skin, the fatty layer of subcutaneous tissue, and the sebaceous glands). Since hair follicles are located in the outer cartilaginous portion of the EAC, this is a common place for furuncles to form. An infection usually occurs when individuals try to clean their ear canal with fingers or improvised aids (paper clips, toothpicks, matches, etc.). The course of this disease can be divided into three stages: infiltration, abscess, and healing. Erythema at the site of inflammation, significant localized swelling of the EAC, and severe pain are hallmarks of the first stage. It is worth mentioning that the deeper parts of the ear and the tympanic membrane remain intact, although they can rarely be examined. After a while (usually within 2–3 days), an abscess begins to form, indicating the second stage of the disease. A furuncle gradually enlarges and becomes fluctuant due to pus accumulation. Additionally, a core of the necrotic material can be seen in its center. During the third stage, scar tissue forms to repair damaged skin.

Bacterial diffuse otitis externa (OE) is an infectious inflammation of the EAC skin that can be classified as acute or chronic (if it lasts for more than 6 weeks). Predisposing factors for OE include skin maceration or damage (e.g., scratching with objects not intended for this purpose), a decreased local pH, and ceruminous gland atrophy. Swimmers are most susceptible to this disease due to prolonged exposure to water and moisture. It is also common in people with carbohydrate metabolism disorders. Moreover, OE can result from a middle ear pathology. In this case, purulent discharge enters the EAC through a perforated tympanic membrane, leading to persistent skin irritation and inflammation.

Clinically, the bacterial diffuse OE is characterized by an area of intensely hyperemic skin and significant swelling of the fatty layer of the subcutaneous tissue, primarily in the cartilaginous portion of the EAC. The swelling can be so severe that the walls of the EAC adhere to each other, resulting in canal obstruction and a failure to visualize the deeper parts of the ear and the tympanic membrane. Abundant ear discharge (otorrhea), consisting of desquamated epidermis or pus, is gradually building up. Occasionally, the inflammation can spread to the tympanic membrane. In this case, it becomes thickened, macerated, and covered with a desquamated epidermis and purulent discharge. The chronic form of the disease is not as pronounced as the acute one. Сoncomitant extraorgan disorders and immune disruptions may transform the bacterial diffuse OE into malignant otitis externa.

Otomycosis is a superficial fungal infection of the EAC associated with Candida albicans and Aspergillus niger. These are opportunistic microorganisms that do not typically cause diseases in healthy individuals but can act as pathogens under the proper circumstances. One of these conditions is skin damage, which makes it possible for a fungal infection to enter the body and spread throughout the system. It usually occurs when an individual cleans the ear canal with cotton swabs and other improvised tools. Predisposing factors also include persistent high humidity in the EAC, metabolic disorders (e.g., diabetes mellitus), and uncontrolled use of topical antibiotics or steroids, which leads to dysbiosis of the skin.

Fungal deposits, or debris, on the slightly erythematous and swollen skin of the EAC are indicative of otomycosis. These deposits vary in color and consistency, depending on the causative pathogen. Infection associated with Candida albicans (candidiasis) generates numerous creamy white patches in the ear canal. In case of Aspergillus niger, examination may reveal thin, loose, black growths with mycelium visible under a microscope. After removing the fungal deposits, the underlying skin appears irritated and macerated.

Malignant (necrotizing) OE, also known as skull base osteomyelitis, is a severe infection of the EAC that affects the skin and the deep underlying tissues (the bones, the cartilage, the cranial nerves, and the parotid gland). It is considered a complication of OE and primarily occurs in individuals with diabetes mellitus, cancer, or other conditions that compromise the immune system, especially in the elderly. The most common causative organisms are Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA). The infection spreads from the ear canal to the cranial base and the jugular foramen via the fissures of Santorini (natural openings in the cartilaginous portion of the EAC), leading to mastoiditis, osteomyelitis of the temporal bone, and inflammation of the cranial nerves. The disease is characterized by necrosis of bone and cartilage tissues, erosions, and ulcerations with granulation tissue formation. The tympanic membrane usually remains intact.

Keratosis obturans (KO) is an inflammatory condition of the EAC defined by the accumulation of desquamated keratinous material that leads to blockage of the ear canal. As a result of the obstruction, swelling and a subsequent bacterial skin infection develop. After pathological depositions have been removed, the skin in the affected area appears thickened and toughened.

Clinical Manifestations

The symptoms of auricular erysipelas include local skin changes as well as signs of general intoxication, such as fever, fatigue, headache, and sometimes vomiting. The affected area is characterized by well-demarcated significant hyperemia and swelling. The involved skin is tender and warm to touch and looks stretched and shiny. The regional lymph nodes become enlarged, tender, and elastic, not adhering to the surrounding tissues. In some cases, inflammation extends beyond the auricle and the earlobe, continuing to the neck, retroauricular, and buccal regions.

In perichondritis, typical symptoms are erythema and heterogeneous swelling of the tissues covering the cartilage of the auricle. Patients usually complain of severe aching or paroxysmal pain in this area. General intoxication symptoms are not typical, but a low-grade fever may occasionally be observed. It is important to note that the inflammation does not spread to the earlobe and the surrounding areas, including the retroauricular region. However, if left untreated, the infection can involve deeper tissues and lead to an auricular abscess. Sometimes the outcome of perichondritis is an ear deformity known as "cauliflower ear", which may develop even with proper treatment.

As mentioned earlier, an auricular abscess typically results from a previous ear injury. Patients usually complain of general intoxication symptoms (fatigue, fever, chills, etc.). On examination, an abscess looks like a cavity filled with pus and surrounded by a capsule. It bulges above the tense and tender skin, and fluctuation is evident. The cavity may become so enlarged that the EAC can no longer be visualized. The deformity of the affected areas, most commonly the triangular and scaphoid fossae, can also be observed. Within 3–4 days, untreated abscesses may spontaneously rupture and drain, resulting in a purulent discharge.

HSV-1 infection is characterized by typical local changes of the skin. During an exacerbation, the affected area becomes hyperemic with multiple painless vesicles on it, which is accompanied by intense itching. The vesicles usually rupture within 2–3 days, resulting in small erosions that become covered with crusts. The healing process takes approximately 5–7 days, during which time the crusts completely disappear and the skin returns to its normal state. Most people do not experience systemic manifestations of infection. However, a low-grade fever and headache may occasionally be observed a few days before the rash develops. It is worth noting that recurrent outbreaks are common in this form of herpetic infection.

Herpes zoster, caused by VZV, differs clinically from HSV-1 infection. As stated above, this form of the disease results from the reactivation of a latent virus in individuals who have had chickenpox. It is more common in older adults and immunocompromised individuals. A few days before the rash appears, there may be severe itching, burning sensations, and acute throbbing pain in the skin area prone to lesions. Patients may also have a fever, headache, and chills. Local changes manifest after a while, often within 2 to 3 days, when vesicles form on the hyperemic skin, spreading along the dermatome. The area of the lesion can be large and affect several adjacent dermatomes since the blisters can merge. It should be noted that the rash always distributes unilaterally. Intense pruritus and pain do not subside over time, which can sometimes lead to psychological issues such as anxiety and insomnia. If scratched, hemorrhagic crusts or secondary bacterial infections may develop. The vesicles rupture within 5 to 7 days, forming erosions that eventually become crusted over. Subsequently, the crusts fall off after the healing process is complete. This area often remains depigmented.

Postherpetic neuralgia (PHN) is the most common long-term complication of herpes zoster. Chronic pain along the affected nerve, which can persist for months or even years, is the main characteristic of this condition.

Ramsay Hunt syndrome occurs when a herpes zoster outbreak affects the geniculate ganglion of the facial nerve. It typically presents with a facial nerve paresis or paralysis associated with a painful vesicular rash on the skin of the external ear. Peripheral facial paresis is determined by unilateral numbness of the facial muscles, flattening of the nasolabial fold, drooping of the eyelid and the corner of the mouth, an inability to close the eye, and lacrimation. It may frequently be accompanied by other signs and symptoms, including dizziness and hyperacusis. The latter one means reduced tolerance to sound that results from paresis of the stapedius muscle, innervated by the facial nerve branch. Additionally, due to damage to the chorda tympani, poor taste perception in the anterior ⅔ of the tongue may be present.

An intense, continuous, aching ear pain (otalgia), that worsens at night and when chewing, is the hallmark of a furuncle of the EAC. The pain can spread to the temporal region, temporomandibular joint, teeth, neck, and, in some cases, a whole half of the head. On examination, the skin of the EAC is hyperemic and swollen. The swelling can be so severe that the walls of the ear canal adhere to each other, resulting in obstruction and failure to visualize the tympanic membrane. This leads to conductive hearing loss, which manifests as autophony, a feeling of fullness, and tinnitus in the affected ear. The auricle and tragus are markedly tender on palpation. General intoxication signs, such as fatigue, headache, fever, chills, and enlarged regional lymphatic nodes, may be observed. If the furuncle is located in the posterosuperior parts of the EAC, the auricular cartilage may become displaced due to significant swelling of the retroauricular tissues. The disease pattern is similar to that of mastoiditis, requiring a thorough differential diagnosis.

Within the next few days, the condition gradually progresses to the abscess stage, when necrosis occurs, resulting in pus accumulation. The pain becomes throbbing but less intense. In some cases, usually within 5-7 days, the furuncle may rupture spontaneously, leading to a profuse purulent or hemorrhagic discharge from the lesion. The patient's condition improves as the pain reduces and the hearing function is restored.

In bacterial diffuse OE, patients complain of impaired hearing and tinnitus in the affected ear, purulent foul-smelling otorrhea, and pain when chewing. The pain intensifies and can radiate to the upper jaw when pressure is applied to the tragus and the auricle is pulled back. The disease progresses rapidly, within a few hours. Otoscopy is often difficult to perform due to significant swelling. General intoxication symptoms are not typical. Occasionally, there may be a low-grade fever, and regional lymph nodes may enlarge.

Otomycosis is a recurrent fungal infection that tends to become chronic. Severe itching and pathological discharge from the EAC are typical clinical manifestations. Sometimes patients try to clean the ear canal and relieve itching by scratching the skin with cotton swabs. However, this leads to a blockage of the EAC due to a plug formation, contributing to conductive hearing loss. Pain and signs of general intoxication are not common, although they may occasionally be present at the beginning of the acute phase of the disease.

Clinical manifestations of malignant (necrotizing) OE include severe otalgia, which worsens at night, a headache on the affected side, and copious, foul-smelling, purulent otorrhea. In severe cases, the affected bones may become exposed. The most common additional symptom at the onset of the disease is conductive hearing loss. It is associated with occlusion of the ear canal by pathological material. As the infection spreads to the deeper structures (e.g., the vestibulocochlear nerve), sensorineural hearing loss may develop. Damage to the facial nerve results in peripheral facial paresis or paralysis, which is manifested by facial asymmetry, drooping of the eyelid and the corner of the mouth, flattening of the nasolabial fold, and lacrimation. OE is usually accompanied by lymphadenitis. Regional lymph nodes become enlarged, tender, and firm, and the overlying skin may be inflamed. General intoxication symptoms are not typical. Malignant OE is a potentially life-threatening disease due to frequent serious complications such as sepsis, dural venous sinus thrombosis, brain abscess, and meningoencephalitis.

Symptoms of KO include persistent otalgia, which intensifies when pressure is applied to the tragus and the auricle is pulled or moved. It is also identified by conductive hearing loss and tinnitus in the affected ear. Otoscopy reveals plugs consisting of desquamated epidermis and earwax, which obstruct the ear canal. These pathological depositions often adhere to the skin. Therefore, they can cause pain when removed.

Diagnosis

A comprehensive approach is required to diagnose infectious diseases of the external ear. It is crucial to take a detailed medical history and examine the structures of the ear (by means of otoscopy). Laboratory tests include a complete blood count and blood biochemistry (inflammatory markers, blood glucose, etc.). To identify the causative pathogen and its antimicrobial susceptibility, an ear discharge culture is performed. Polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), and serological tests can be used to detect a viral pathogen. Some complications may necessitate a CT or MRI scan. Additional diagnostic options include blood culture and lumbar puncture.

A particularly thorough diagnostic evaluation is needed for patients with malignant (necrotizing) OE. It is mandatory to perform a temporal bone CT, a brain MRI, and an ultrasound of the parotid glands. Culture of ear discharge and antimicrobial susceptibility testing are also of great importance. Another useful diagnostic tool is a biopsy of affected tissues, which can help diagnose a condition. HIV testing is typically performed to rule out immunodeficiency. Additional diagnostic options include gallium-67 and technetium-99 scintigraphy and lumbar puncture (if indicated).

Patients with malignant OE require routine clinical and laboratory monitoring, such as regular measurement of blood glucose, and neurology consultation to assess the function of the cranial nerves.

Treatment

Antibiotic therapy is the main treatment option for auricular infections since the principal causative pathogens are bacteria. Systemic antibiotics are administered orally or parenterally, at the discretion of a physician. Penicillins (β-lactam antibiotics) are the first-line therapy and can be used in combination with fluoroquinolones. Treatment can be subsequently adjusted based on the results of cultures and antimicrobial susceptibility. Another crucial part of efficient therapy is applying antiseptic medications locally to the affected area. This helps dry the wound and speed up the healing process.

Patients with an auricle abscess should be treated surgically. One of the options is the ‘incision and drainage’ (I&D) procedure. This is when the abscess cavity is cut open to evacuate pus, and then a drain tube is placed. After that, an aseptic dressing is applied. It should be changed on a daily basis until complete recovery. During the healing stage, topical medications for tissue repair and regeneration can be used.

Treatment of herpetic infections includes antiviral medications, namely acyclovir, valacyclovir, and famciclovir (treatment of choice). Symptomatic treatment is also provided and may include infusion therapy, antihistamines, nonsteroidal anti-inflammatory drugs (NSAIDs), and, in severe cases, glucocorticosteroids. In addition, antiseptic solutions are regularly applied to the affected areas of the skin. Pain management is another important part of therapy, especially in postherpetic neuralgia. Medications used for this purpose include metamizole, gabapentin, pregabalin, and tricyclic antidepressants. In cases of intense pain, opioid analgesics (e.g., tramadol and morphine) can be administered.

OE is primarily treated with topical medications. Combination drugs containing antibacterial, steroid, and analgesic components are especially effective. Please note that it is recommended to use medications in a solution form. This is because using other dosage forms, such as ointments, may lead to ear canal plugs composed of a medicinal product, wax, hair, and desquamated epithelium. Moreover, it may cause inadequate ventilation, increasing the risk of long-term and recurrent diseases. Adjunctive treatment with oral antibiotics should be considered if the infection is severe or local treatment is ineffective.

In cases of significant swelling of the EAC, an ear tampon soaked with a medicinal solution is inserted into the canal, allowing the drug to reach the deeper structures. This procedure is usually repeated 3–5 times a day. As swelling decreases, the tampon no longer packs the ear canal and falls out spontaneously, making it possible to insert a medicinal product. If the patient complains of severe pain, oral analgesics are prescribed. It is also recommended to clean the external auditory canal regularly, including rinsing with antiseptic solutions.

The furuncle of the EAC should be treated surgically under local anesthesia if the condition progresses to the abscess stage. The most prominent bulging of the suppurative focus is dissected, debrided, and drained, followed by the application of an aseptic dressing. After the procedure, the dressing should be changed daily.

Special attention should be paid to eliminating all predisposing factors for OE, which is the key to a favorable outcome. For instance, the most effective way to prevent “swimmer's ear” (OE) is to keep the ears dry after water exposure by using a hair dryer or alcohol drops. In addition, to prevent reinfection after successful treatment of an acute disease, the pH of the skin surface should be reduced using ear cleaning solutions containing acetic or boric acid.

Treatment of otomycosis involves mechanical removal of fungal deposits, dry cleaning of the ear canal, and applying topical antifungal medications. Please note that combination drugs containing antibacterial and steroid components should be avoided. It is also not recommended to pack the EAC with cotton wool or gauze swabs. Otherwise, it may lead to inadequate ear ventilation, increasing the risk of recurrent infection.

Patients with malignant OE must be admitted to a hospital. In severe cases, they may require treatment in an intensive care unit or high dependency unit. The initial empirical antimicrobial therapy includes fluoroquinolones and penicillins. Subsequently, treatment is adjusted based on the results of cultures and antimicrobial susceptibility. In addition to antibiotics, local treatment of the lesions is provided: antiseptic solutions and aseptic dressings with ointments containing antibacterial and steroid components are applied regularly. If necessary, surgical debridement is performed. Blood glucose control is also particularly important for the treatment to be successful.

There are several steps in the treatment of KO. First, any pathological masses should be mechanically removed from the ear canal. Before the procedure, a patient must receive adequate analgesia, and, in some cases, general anesthesia may be required. The next step is local treatment with combination drugs containing antibacterial and steroid components. As mentioned earlier, preference should be given to drugs in the form of solutions. To prevent recurrent infection, this group of patients requires periodic instillation of a 3% hydrogen peroxide solution into the ear canal and regular visits to an ENT specialist for timely cleaning of the EAC.