Collecting, processing, and evaluating samples for ear cytology is a crucial skill for veterinary technicians and nurses. Not only is ear cytology a cost-effective method, but it also provides valuable insights into pruritic ears. In this article, we will explore the reasons for performing ear cytology and guide you through the step-by-step process of collecting, staining, and evaluating samples.
When to Perform Ear Cytology
Otitis externa, characterized by clinical signs such as itching and irritation, is one of the most common reasons why animals seek veterinary care. To identify or rule out microbial otic infections in animals presenting with these signs, ear cytology is a quick and routine procedure that can be performed. With the increasing concern of antimicrobial resistance, selective treatment options are crucial in combating infectious organisms. By performing ear cytology and correctly identifying microorganisms, skilled veterinary nurses can aid in the veterinarian’s diagnosis. This invaluable information assists in selecting the most effective therapy or further tests, such as culture and sensitivity. Additionally, ear cytology serves as a monitoring tool during therapy, with regular rechecks to evaluate progress until there is no evidence of infection.
Causes of Otitis Externa
The classification system known as PSPP helps identify the causes of otitis externa. PSPP stands for primary, secondary, predisposing, and perpetuating factors. Ear cytology plays a vital role in identifying primary, secondary, and perpetuating factors.
Primary factors are the ones that cause infections in healthy ears. Ear sampling can detect specific primary causes such as ear mites in dogs and cats (Otodectes cynotis), rabbits and goats (Psoroptes cuniculi), and dogs (Otobius megnini). Other less common but documented parasitic primary causes include various species of Demodex, Notoedres cati, Sarcoptes scabiei, Cheyletiella species, Eutrombicula alfreddugesi, and Neotrombicula autumnalis.
Secondary factors involve opportunistic bacteria and yeast overgrowth, with Malassezia pachydermatis being the most commonly detected organism through ear sampling and culture.
Predisposing factors for otitis externa include ear conformation and anatomy that make ears prone to infection, such as pendulous pinnae, hypertrichosis, and stenotic ear canals. Environmental factors like frequent swimming, bathing, or excessive ear cleaning can contribute to the development of otitis externa. Systemic conditions such as immunosuppression or hypoadrenocorticism, as well as obstructions like polyps or neoplastic growths, also play a role.
Perpetuating factors include opportunistic bacteria, yeast overgrowth, otitis media, cellular hyperplasia, ear canal edema, calcification, and excessive fluid or debris within the middle ear and ear canal.
Sample Collection and Preparation
During a physical and otoscopic examination of the ear, specimens from the external ear canal are collected. Ideally, samples are collected before the use of any aural cleansers or medications. In cases of otitis media with intact tympanic membranes, a skilled veterinarian may perform a myringotomy to collect a culture for bacterial analysis. The following supplies are needed for sample collection and analysis:
- Otoscope
- Cotton-tipped swabs
- Microscope slides (preferably with frosted edges for clear labeling)
- Mineral oil for mite identification
- Romanowsky-type cytology stains (dedicated cytology stain set preferred to avoid contamination)
- Microscope with 100x objective
By following the proper collection and preparation techniques, veterinary technicians and nurses can ensure accurate and reliable ear cytology results, helping veterinarians make informed decisions for effective treatment.
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