How and When to Perform Ear Cytology: Recognizing the Clinical Signs
Constant head shaking? Ear scratching? Foul-smelling discharge from the ears? These are all common reasons for pet owners to take their dog or cat to the veterinarian, as they are obvious signs of otitis externa (OE)—an inflammation of the ear that can cause discomfort and pain that can become chronic or lead to more severe complications if left untreated.
Ear cytology is a simple and important diagnostic test for these cases. There are other clinical signs where this diagnostic test is needed and can provide information beyond treating the infection. With this in mind, let's explore when to perform this assessment, how to interpret and use the results, and what methods are available to optimize testing and treatment.
Clinical Signs Indicating When to Perform Ear Cytology
Cytology should be performed in all cases of abnormal ear discharge to determine the cause of the infection. Here are some of the signs associated with OE:
- Head shaking
- Ear scratching or rubbing
- Foul-smelling or copious discharge from the ears
- Pinnal marginal alopecia or follicular casts
- Concave pinna erythema, edema, lichenification, and hyperpigmentation
- Convex pinna alopecia and erythema
- Periauricular acute moist dermatitis
- Head tilt, circling, and nystagmus (peripheral vestibular signs)
It's also important to perform cytology on every ear that has a history of OE to confirm that the infection and inflammation have truly resolved. A complete physical examination should include evaluation of the pinnae and otoscopic exam of both ears.
Routine evaluation of the ear canals allows you to detect subtle changes in discharge amount and character, ear canal inflammation, and tympanic membrane integrity.
How to Perform Ear Cytology
Ear cytology is a simple diagnostic test that involves gently swabbing the junction of the vertical and horizontal ear canals, then rolling the sample on a glass slide. Heat fixation is not necessary. The slide is stained with a standard in-practice quick stain kit and evaluated under the microscope. Depending on a practice's workflow and staffing, this process can take several minutes, and there might not be a trained technician available to interpret the slide.
New cytology technologies, including analyzers that provide real-time quantitative results, are available to speed up this workflow. These analyzers can perform the processing and interpretation portion of cytology—without the need for slides and staining—which can help free up technician time and produce a standardized report for inclusion in the medical record, giving veterinarians time back, too.
Using Ear Cytology Results
Ear cytology gives the clinician information on which organism(s) and inflammatory cells are present in the external ear canal. These typically include Malassezia, Staphylococcus, and in some cases, Corynebacterium or Pseudomonas. While many of the products available to treat OE are similar in their composition (e.g., antibiotic, antifungal, or corticosteroid), the value of knowing which organisms and inflammatory cells are present lies in knowing which adjunctive treatments might be necessary and in determining prognosis.
Adjunctive treatments might include systemic antifungals, corticosteroids, otic irrigation for suppurative Malassezia OE, or products with biofilm-reducing properties and otic irrigation for Pseudomonas infections. Prognosis can vary from excellent for a dog with non-inflamed Malassezia OE to guarded in a brachycephalic dog with multi-drug resistant Pseudomonas OE.
Knowing which organisms are present also provides information on the likelihood that OE might progress to otitis media (OM). Pathogens, such as Pseudomonas, might be more likely to erode the tympanic membrane and lead to OM. Knowing this organism is present is an indication for intensive treatment and monitoring.
By leveraging new, innovative, and automated technology, veterinarians can perform cytology faster and produce more accurate results, enabling the early identification and diagnosis of OE. This can help ensure that pets of all types can receive the treatment they need when they need it.
