Cotton bud in external ear canal causing necrotising otitis externa and subdural abscess

Abstract

Necrotising otitis externa (NOE) is an infection originating in the soft tissues of the external auditory canal (EAC) spreading to the surrounding bone and rarely causing intracranial complications. It is usually caused by Pseudomonas aeruginosa and has historically occurred in elderly patients with diabetes or immunodeficiency. EAC foreign body is a risk factor for otitis externa but has not been described in NOE. A healthy 31-year-old man presented with new-onset seizures and worsening left-sided otalgia and otorrhoea. Brain imaging revealed left temporal subdural abscesses superior to the petrous bone. A retained cotton bud was identified in the left EAC, along with osseocartilaginous junction and mastoid granulation tissue. The foreign body was removed; a cortical mastoidectomy performed and intravenous antibiotic administered. At 10 weeks, the patient remained well, with no neurological deficit and no residual ear symptoms, and CT demonstrated complete resolution of the intracranial abscesses.

Background

Necrotising (malignant) otitis externa (NOE) is an infection that originates in the soft tissues of the external auditory canal (EAC) with inflammation of the underlying temporal bone, which can progress to skull base osteomyelitis. The causative organism is usually Pseudomonas aeruginosa, and the disease has historically been described in elderly patients with diabetes or other immunodeficiencies. Cranial neuropathies, and rarely, intracranial complications, such as meningitis, dural sinus thrombosis and intracranial abscess, can occur. The presence of a foreign body in the EAC is a recognised risk factor for developing otitis externa, but NOE due to retained foreign body has not previously been described.

Case presentation

A 31-year-old man was brought to the emergency department by ambulance after collapsing, with witnessed seizures of new onset. The normally fit and well man reported 10 days history of left-sided otalgia and otorrhoea, progressing to left-sided headaches with associated nausea and vomiting in the 4 days prior to presentation. He had received two different courses of oral antibiotics from his general practitioner for a ‘severe ear infection’ and had a background of intermittent left ear pain and hearing loss for the past 5 years. He also admitted to being more forgetful of names in recent days, although denied other neurological symptoms. Examination found him confused and drowsy in a likely postictal state, with Glasgow Coma Score of 14/15.¹ Abbreviated mental test score was 9/10. Meningism was absent; pupils were equal and reactive to light, sized 3 mm; and examination of cranial nerve function and peripheral neurology was normal, except for reduced hearing in the left ear. There was discharge in the left EAC, obscuring a view of the tympanic membrane but mastoid tenderness was absent. He was afebrile, and general physical examination was otherwise unremarkable.

Investigations

Computed tomography (CT) imaging of the brain revealed a left superior tentorial subdural abscess as well as subtle erosion of bony EAC and mastoid (figure 1, day 0). In the temporal bone, the left middle ear was opacified and the left external ear canal was filled with soft-tissue density material. There was no erosion of the ossicles, tegmen tympani or inner ear. Blood tests on admission showed a haemoglobin of 113 g/L, white cell count 10.18×10⁹/L, neutrophil count 8.96×10⁹/L, C-reactive protein 66 mg/L, lactate 1.1 mmol/L and normal clotting, renal function and electrolytes. Empirical antibiotic therapy was initiated and magnetic resonance imaging (MRI) of the brain was arranged to better characterise and delineate the lesion. This demonstrated a 29×17×9 mm subdural collection at the surface of the left tentorial leaflet, superior to the petrous bone and an adjacent, separate, smaller (16×11×9 mm) collection (figure 2, figure 3). Both demonstrated an enhancing, thick wall and restricted diffusion, indicating purulent content. Spectroscopy indicated increased lactate, further supporting the presence of an abscess/subdural empyema. Bone marrow changes consistent with osteomyelitis were noted in the petrous temporal bone.

Figure 1.

CT head series at day 0, 6, 17, 28 and week 15 demonstrating initially left temporal subdural abscess and later, left occipital subdural abscess. Both have completely resolved on the final scan including any oedema.

Figure 2.

Axial MRI image showing two discrete temporal subdural collections. Arrow denotes a larger, posteromedial collection. Arrow denotes a smaller, posterolateral collection.

Figure 3.

Sagittal (upper images) and coronal (lower images) MRI brain images of two discrete temporal subdural abscesses. Arrow denotes a larger, posteromedial collection. Arrow denotes a smaller, posterolateral collection.

A swab of the ear discharge was sent for microbiological assessment. Subsequently, P. aeruginosa sensitive to meropenem and ciprofloxacin was cultured.

Treatment

Initial treatment was with IV cefotaxime for clinical suspicion of bacterial meningitis. With the CT scan result, and following discussion with neurosurgeons, IV vancomycin, meropenem, levetiracetam and dexamethasone were administered, and arrangements were made for the transfer of the patient to the care of the neurosurgical team.

Following assessment by an otolaryngologist, the decision was taken to explore the ear under general anaesthesia. The EAC was inflamed and filled with discharge/debris with granulation tissue at the osseocartilaginous junction and overlying impacted cotton bud. The cotton bud was removed, ear canal cleared of debris and a cortical mastoidectomy performed. The tympanic membrane was intact, and no evidence of cholesteatoma was found, but granulation tissue and inflamed mucosa were present in the mastoid antrum. These findings, together with the radiological findings and swab positive for pseudomonas, led to the diagnosis of NOE. This was felt to be secondary to retained cotton bud and had become complicated by intracranial infection. Biopsy of EAC tissue was negative for malignancy.

Conservative management of the subdural abscesses and NOE was continued, with intravenous meropenem and oral ciprofloxacin (following discussion with a clinical microbiologist). A repeat CT scan was performed at day 6, which demonstrated shrinkage of the abscess. The patient was clinically well and was discharged from the hospital on day 7, with ongoing oral and intravenous antibiotics (via a peripherally inserted central catheter) delivered at home for a total of 8 weeks.

Outcome and follow-up

Follow-up CT imaging at day 17 showed improvement of the temporal subdural abscess, but formation of a new occipital subdural abscess. This had reduced in size on interval CT imaging at day 28. A CT scan performed at 10 weeks demonstrated complete resolution of the previously visualised abscesses and surrounding oedema. At the completion of his course of antibiotics, the patient remained systemically well with no neurological deficit and no residual ear symptoms. Most importantly, he is no longer using cotton buds to clean his ears!

Discussion

Although the presentation, in this case, was atypical for NOE (new-onset seizures), features of severe otalgia, otorrhoea, hearing loss, unilateral headache and elevated c-reactive protein provide diagnostic clues of NOE.^{2 3} In this case, the patient was appropriately referred for an otological review. The finding of granulation tissue at the osseocartilaginous junction and radiological features of temporal bone erosion and osteomyelitis also support the diagnosis of NOE.⁴

A histopathological analysis of cases of NOE demonstrated that infection spreads from the EAC to the stylomastoid and jugular foramina, and mastoid system (via the tympanomastoid suture). This can result in septic thrombosis of the lateral venous sinus and infection can subsequently extend via the posterior and/or middle fossa surfaces of the petrous bone to the petrous apex.⁵ The findings of granulation tissue at the osseocartilaginous junction and within the mastoid antrum, as well as the location of the abscess close to the petrous apex, in this case, support these findings.

A far more common mechanism for infection to spread from the ear to the central nervous system to cause intracranial abscess is via a breach in the tegmen tympani due to suppurative otitis media, causing 94% of otogenic intracranial abscess and complicating approximately 0.26% of cases of suppurative otitis media.^{6 7} Temporal lobe abscess has also been described in a patient with ectodermal dysplasia.⁸ Intracranial complications in the context of NOE are rare (0.3%), and usually denote advanced disease and grave prognosis.² Contrarily, in this case, there was no evidence of advanced disease on imaging and the patient avoided cranial neuropathies, making a full recovery with limited surgery and no intracranial procedure. Another previously described case of NOE complicated by cerebral abscess was successfully treated with extensive surgical debridement and abscess drainage, although this was in an older (60-year-old) patient with diabetes.⁹ Similarly, aggressive treatment was successful in a healthy 60-year-old man free of diabetes and immunocompromise who developed NOE complicated by epidural abscess.¹⁰

NOE remains a condition with various challenges to its management. A systematic review identified a lack of evidence regarding diagnostic criteria, treatment protocols and follow-up criteria, with no clinical trials evaluating the effectiveness of treatment options. Management, therefore, appears to rely on empirical indexes of suspicion and personal experience of clinicians. Despite the lack of strong evidence, management protocols have been suggested.¹¹

Another controversy in the approach to NOE is imaging. CT and MRI may both have a role in its evaluation, with CT being superior for demonstrating the extent of bony disease and MRI superior for soft-tissue disease extent. However, bone erosion and changes in skull base density detectable by these modalities may only be present in advanced disease. Furthermore, these changes take a long time to regress on imaging after resolution of the infection, making them inadequate for follow-up imaging. Gallium-labelled and technetium-labelled imaging have emerged as adjunct techniques for diagnosis as well as determining the resolution of NOE. ^99mTc-Sulesomab in particular shows promise for diagnosis as well as determining response to treatment and guiding ongoing management.¹²

Although uncommon, NOE has been described in relatively young individuals without diabetes or immunocompromise.¹³ In fact, the description of NOE as a disease of exclusively older people with diabetes may not be true: between 2002 and 2013, elderly, diabetic patients accounted for only 22.7% of NOE cases.¹⁴ The incidence of NOE also appears to be increasing, with a sixfold increase in the number of cases from 1999 to 2013.¹⁵

The use of cotton buds inside ears is common and has long been recognised to cause several complications including trauma, tympanic membrane perforation, impacted earwax, infection and retention of the cotton bud.¹⁶ Although foreign material (particularly cotton bud) in the EAC is a recognised risk factor for developing otitis externa,¹⁷ the present case describes for the first time that we are aware of a case of NOE and intracranial abscess secondary to a retained cotton bud.

It is clear that the entity of NOE is evolving, and features of NOE displayed in any individual must now be taken seriously, not only in elderly patients with diabetes or immunocompromise. The present case further reiterates the dangers of cotton bud use, and the importance of foreign body removal if identified in the EAC. It also highlights that in a young, healthy individual with NOE complicated by subdural abscess, conservative treatment with long-term antibiotic therapy may be appropriate.

Learning points.

• Recent studies show that the incidence of necrotising otitis externa (NOE) is increasing, and it is more frequently affecting younger and healthy individuals, as with the case discussed herein.

• This case suggests that intracranial abscess may form in fairly limited disease and may have a good prognosis when it occurs in a healthy young individual.

• Cotton bud use in the ear canal is a risk factor for multiple otological conditions, including otitis externa.

• This case suggests that a retained cotton bud may also cause NOE.

• This case highlights that limited surgical intervention and long-term antibiotics can have an excellent outcome for NOE complicated by subdural abscess in a healthy, young individual.