Differential Diagnosis for Acute Otitis Externa with Black and Malodorous Fluid

• Single most likely diagnosis:
  • Pseudomonas infection: This is the most likely cause due to the presence of black and malodorous fluid, which is characteristic of Pseudomonas infections, particularly in the context of otitis externa. Pseudomonas aeruginosa is known to produce pigments that can cause the discharge to appear black or greenish.
• Other Likely diagnoses:
  • Fungal infection: Fungal infections can also cause otitis externa and may present with malodorous discharge, although the color might not typically be black. Fungi like Aspergillus can cause infections in this area, especially in immunocompromised patients.
  • Staphylococcus infection: While Staphylococcus aureus can cause otitis externa, it is less commonly associated with black, malodorous discharge compared to Pseudomonas. However, it remains a possible cause, especially if the infection is severe or if there's an abscess.
• Do Not Miss diagnoses:
  • Malignant otitis externa: This is a severe form of otitis externa that can occur, particularly in diabetic or immunocompromised patients. It is typically caused by Pseudomonas aeruginosa and can lead to significant morbidity and mortality if not promptly treated. The presence of black, malodorous discharge could be indicative of this condition, especially in high-risk patients.
• Rare diagnoses:
  • Allergic reaction: While an allergic reaction could potentially cause some symptoms of otitis externa, such as itching or redness, it would not typically cause black, malodorous fluid. Allergic reactions are more likely to cause a clear or serous discharge.
  • Other bacterial infections: Other bacteria could potentially cause otitis externa, but they are less likely to cause the specific symptom of black, malodorous discharge. Examples might include infections caused by Streptococcus or Haemophilus species, though these would be less common causes of this particular presentation.