Diagnosis

• consider a diagnosis of malignant otitis externa with features such as (1,2):
  • fever
  • disproportionate pain
  • or a poor response to first line treatment, particularly in people with diabetes or immunocompromise
    • maintain a high index of suspicion in patients with risk factors, in particular diabetes, who have otitis externa that is not responding to initial treatment
  • associated vertigo and hearing loss may indicate malignant otitis externa (3)
    
    
• lavage of the ear canal for cerumen impaction in elderly or diabetic patients, however, has been implicated as a contributing factor in malignant otitis
  externa (3)
• irrigation of the ear canal with tap water is a potential iatrogenic factor
  
  
• P aeruginosa is isolated from exudate in the ear canal in more than 90% of cases
  
  
• initial clinical features are those of the initiating acute otitis externa, but untreated disease develops into a skull base osteomyelitis that
  can invade soft tissue, the middle ear, inner ear, or brain
  • facial nerve paralysis may be an early sign, with the glossopharyngeal and spinal accessory nerves less frequently involved
    
    
• granulation tissue or exposed bone in the floor of the osseocartilaginous junction may occur
  • pathognomonic of malignant otitis externa
    
    
• if you suspect malignant otitis externa arrange an urgent (same day) ear, nose, and throat (ENT) review. A computed tomography imaging scan is typically required to confirm the diagnosis

Reference:

1. Sander R. Otitis Externa: A Practical Guide to Treatment and Prevention.Am Fam Physician 2001;63:927-36,941-2.
2. Barry V et al. 10-Minute Consultation - Otitis externa. BMJ2021;372:n714http://dx.doi.org/10.1136/bmj.n714
3. Rosenfeld RM, Schwartz SR, Cannon CR, etal. Clinical practice guideline: acute otitis externa.Otolaryngol Head Neck Surg2014;150(Suppl):S1-24.doi: 10.1177/0194599813517083 pmid: 24491310