Serious External Ear Infections: Scout, Labrador Retriever
By Dr. Frank Coons
One of the most common conditions seen by small animal veterinarians is Otitis Externa- or external ear infection. Most of these are readily treated. The most common causes are yeast and bacteria, such as staph or strep. Many dogs have underlying conditions that predispose them to ear infections, such as allergy, low thyroid levels or Cushing’s disease.
The case we are profiling this month is a patient with a more serious ear infection caused by the bacteria Pseudomonas. “Scout” is a 3-year-old neutered male chocolate Labrador Retriever. He has a history of mild seasonal allergic skin disease and is in very good general health.
Scout was presented to us with a history of sudden pain and itching in the left ear. The owners also noted a bad odor in this ear. On presentation, the left ear was markedly inflamed with a mucoid discharge and was very painful upon exam. The right ear appeared normal. Deep examination of the ear under light anesthesia revealed a moderate amount of yellow liquid discharge, but no foreign body (fox tail, seed, etc). The ear drum was intact. Because the degree of inflammation was so intense, and cytology was not consistent with a simple yeast infection, the decision was made to culture the ear. The ear was then thoroughly cleaned and flushed with sterile saline. Scout was released later that day on a broad spectrum topical ear medication, awaiting culture results. Several days later the culture was positive for Pseudomonas aeruginosa. This organism favors moist areas and can cause significant ulceration and scarring over time.
The species is notorious for developing antibiotic resistance. In addition, the bacteria produce a mucinous coating that prevents penetration of antibiotics through the cell wall. It favors a neutral or basic environment. When a Pseudomonas infection becomes chronic, it creates scar tissue. These factors can add up to an extremely difficult problem that can take months of effort, medications and even surgery to eliminate. Consequences can range from hearing loss to middle ear infection and meningitis.
Scout was started on oral antibiotics. In addition, we have prescribed a topical cleanser that removes the mucinous debris, acidifies the ear canal and allows better penetration of the antibiotic. Follow up exams will be required to ensure complete resolution of the infection.
This case demonstrates the need for identifying the less common causes of otherwise common problems- what clinicians would call an “index of suspicion.” With Scout, we hope that this will result in complete elimination of a potentially severe, chronic infection. With Pseudomonas ear infections, early recognition and aggressive treatment are key.
