When general practitioners encounter a lump or bump to diagnose, they usually harken back to phrases they heard in veterinary school such as, “tape, scrape, and DTM,” or “if it looks like ringworm, it’s probably staph,” or “garbage in, garbage out.” However, the one catch phrase that has proved the most valuable in my veterinary career so far has been “stick it and submit it.” These simple expressions only echo the importance of a diagnostic modality that is simple, quick, and informative—cytology.
Cytology vs. histopathology
We know diagnosing skin disease is going to take several visits and testing, which is why a thorough physical examination and good history from pet owners is an essential first step. Obviously, severity and duration of clinical signs determines diagnostic workup, and medical history, and physical examination will guide diagnosis. However, cytology can add tremendous value.
Cytology is the microscopic evaluation of cells collected from both internal and external locations of our veterinary patients. Most commonly, we are presented with cases when owners notice a “lump or bump” and we are left to collect samples via aspirations of bodily fluids on various locations from the mouth to the ear pinna.
Cytology can tell us whether a lesion is inflammatory or neoplastic. If it is inflammatory, then we can determine the underlying cause of etiology, such as parasitic, bacterial, fungal or allergic.
Performed easily in the general practice setting with supplies—slides, syringes, and needles—readily available in any exam room, cytology is more affordable when compared to histopathology if one was comparing costs to surgical preparation of the lesion, sedation or anesthesia, and follow-up care.
In addition, most veterinary patients and pet owners are amenable to the fact we can acquire cytology samples quickly and they do not have to return for additional appointments or drop-offs.
Cytology can help us evaluate the general patterns of interpretation into several categories that can vary from nondiagnostic, no cytologic abnormalities, inflammation, hyperplasia, or dysplasia and neoplasia.
Given the variability of cytology, many veterinarians send their samples to their reference laboratory as many offer a fast turn-around time, detailed reports, and digital images. When using a reference laboratory, it is important to remember sample quality correlates directly with the quality of the diagnostic evaluation and potential confirmatory diagnosis, hence the phrase, “garbage in, garbage out.”
Several “pearls of practice” when submitting a cytology sample to a reference lab include:
1) Label the frosted end of the slide with the name and site of the patient. Pencil is preferred.
2) Do not put cytology samples in with any containers containing formalin. Formalin fumes can interfere with staining and thus cell identification. Not to mention, formalin is a biohazard.
3) Submit all your smears, even the ones you looked at in-clinic. Those slides could be highly cellular and provide a wider breadth of cytological information. Two to three slides per site is optimal.
4) Do not heat-fix or refrigerate any samples. A good reference laboratory will have a well-developed protocol of processing and staining mechanisms that are similar to what is done in human laboratories. Ideally, all pathology samples go through high-quality, state-of-the art digital analysis. Allow the smears to air dry and protect them from moisture in a slide container.
Cytology at the point of care
Although reference laboratories provide a valuable service that is reliable, efficient, and cost-effective, technological advancements have brought cytology to the point of care, giving general practitioners access to a global network of certified clinical pathologists from their own practice.
Point-of-care (POC) digital cytology scanners allow clinics to have a pathologist verify critical information they need to effectively diagnose and treat their patients faster than the traditional methods of waiting for results, while fending off calls from understandably anxious owners.
Some may view these scanners as “too techy,” or feel they will not be able to keep up with the maintenance of the machine. However, as there is no special staining procedures or slide cartridges to manage, this new generation of POC scanners is virtually maintenance-free.
Inflammatory causes can look very similar. Cytology preparations, such as for the ear and skin (mite preparations, impression smears, and tissues scrapings) can help rule out other disease processes.
I’m all ears!
Ear cytology with a cotton-tipped applicator is another route through which we can determine if there is cytologically no abnormalities, such as cellular debris, or if there is a bacterial or fungal infection needing medical intervention. Collection of ear cytology can prove tricky, as a lot of the debris can sometimes be deeper in the canal.
Pro-tip: When collecting ear cytology, pull the ear flap up, extending the canal to get the most exudate and debris. After collecting, roll the sample on the glass slide with the frosted area facing you. Place right on the right side and left on the left side. You do not have to necessarily heat-fix the slide. Heat fixing for ear slides or impression smears (think oily and greasy skin) was thought to enhance Malassezia or bacteria adherence to the slide.
This is still a controversial statement, as many microbiologists say heat fixing kills the organism, and the methanol in the Diff-Quik stain achieves the same goal as heat fixing. Many also feel it can cause cellular damage and lead to artifacts on the slides. Many veterinary dermatologists agree with microbiologists about heat fixing slides and argue cytology might be able to provide us with acantholytic cells or mast cells which might mean more serious pathology for the patient.
To culture or not to culture
Whenever you see rods, you should always run a culture and sensitivity. Cytology is not the one-stop-shop in this case, as it only gives you the numerical count of the organisms present. We are all familiar with the 2+ cocci, 3+ rods in our medical notes, but this does not identify the species or give you the appropriate antimicrobial susceptibility.
Other inflammatory cells, such as intact or degenerative neutrophils, can also be found with bacteria that will help us determine if the infection is active. The significance of findings in bacterial rods in the ear can help the general practitioner take a deeper dive into more aggressive therapy in treating otitis media, instead of just an otitis externa case.
Preparing for a mite prep may mean either from the skin or from the ear. Obtaining cytology using this technique is a simple and cost-effective way to get this useful information of whether your patient has Otodectes in the ear or Sarcoptes on the skin.
Pro-tip: Use your cotton-tipped applicator to remove debris from the ear and apply it on a slide with at least one to two drops of mineral oil already on the slide. You then can mix the debris with more mineral oil to allow for even distribution.
If you are collecting a mite prep on the skin, it is always best to use a dulled No.10 scalpel blade and always scrape in the direction of the hair, making sure you apply even pressure to the area as if you were scraping ice off a windshield in a Minnesota winter. You always want to apply mineral oil to the blade, the slide, and the lesion.
Given Demodex mites live in the hair follicle, which require deep skin scrapes, I advise colleagues to pinch the area of skin before you begin to scrape when you need only superficial scrapings. You can then place a coverslip after collecting the sample to allow for better scanning ability on the microscope stage at 10x magnification.
Impression smears can be made from a variety of lesions. Most are useful in exudative skin lesions, dry-crusting type lesions, or lichenified areas appearing greasy to the touch. Skin lesions, such as pustules or epidermal collarettes, are great to apply on a slide, as well. You can rupture a pustule with a needle and smear the contents of it on a slide to achieve a monolayer of cells that will prove diagnostic when stained.
Use moderate pressure when applying the lesion to slide. Although we want exudate and material to be visible on the slide, avoid smearing thick layers. This might hinder the ability to get good cytological understanding of the flora on the skin. My favorite use of impression smears are the greasy lesions on bulldogs that can be suggestive of Malassezia dermatitis, but can also be present on mixed bacterial and fungal skin infections.
According to many veterinary dermatologists, clinically, lichenification, hyperpigmentation, and a greasy feel/odor to an animal’s skin are suggestive of Malassezia, but do not be fooled as it, too, can be present with a chronic bacterial infection. Performing skin cytology will enable a proper diagnosis that you can feel confident in sharing with your pet’s family.
Cytology is an amazing tool that can provide a peek into the disease process occurring on your patients, making treatment plans more accessible. Do not fret if there is a challenging case. Reference laboratory pathologies are always available to collaborate, continuing best medicine practices with detailed and comprehensive descriptions and interpretations for every case. When in doubt, just send it out!
Jennifer Lopez, DVM, MBA, began her veterinary career as a technician at the University of Florida, working in both the clinical and research departments of dermatology. She has been published in more than eight articles in Veterinary Dermatology and American Veterinary Journal of Research. Dr. Lopez has been a part of the Mars family for over eight years and the Antech Diagnostics and Imaging family for over two years as professional services veterinarian serving the northeast zone. She continues to practice covering relief shifts in New York City where she lives with her fur-family: Roxy Razzle Dazzle, and Pickle Dickle, her two French bulldogs, and her miniature poodle, named Poodle.