Diagnosing and managing ear disease (Proceedings)
Several different diagnostic and medical treatment options exist for treating otitis in dogs and cats. It is important that the veterinarian know all of the options that are available so that they can make recommendations to the pet owner. We will discuss all of the diagnostic and many of the treatment options for otitis.
The diagnostic tests that are selected for each patient will vary depending on the chronicity and severity of the ear disease. All cases, even first time cases, should have a cytology and an otoscopic examination (standard handheld otoscope or video otoscope) as part of the work-up. More advanced cases will require bacterial cultures, video otoscopic examination, imaging (bulla series radiographs, CT, MRI), biopsies, and myringotomy. One or more of these diagnostic tests may be necessary.Cytology
Ear swab cytologies should be performed on every ear case. This diagnostic test takes little time to perform and the amount of information gained is invaluable. Inflammatory cells with cocci most often indicate Staphylococcus spp. or Streptococcus spp. infection. Inflammatory cells with rods often indicate one or more of the following bacteria: Pseudomonas spp., Proteus spp., Klebsiella spp. or Corynebacteria spp. The only two options for the presence of yeast on cytology are: Malassezia spp. (most common) or Candida spp. (rare). Keratin and glandular secretions and no inflammatory cells suggest an endocrine or seborrheic disease. Parasites are easy to find and identify on cytological preparations.
Otoscopic examination is useful for determining whether polyps, foreign bodies, tumors, parasites (ie ear mites or ticks) or ear canal obstructions are present. In addition, an otoscopic examination is required to help to determine whether an ear drum is intact. It is important to know whether an ear drum is intact because the treatment options will be different depending on if the ear drum is present. If the ear drum is not present then ototoxicity is a bigger problem with topical therapies and very few are safe to use in a ruptured eardrum.
Identification of primary lesions on the pinna such as pustules or ulcers can be useful. Pustules on the ears are suspicious for an autoimmune skin disease (ie most likely pemphigus). Ulcers can be present with a severe infection (ie Pseudomonas spp.), drug eruption or autoimmune/congenital skin disease (ie bullous pemphigoid or dermatomyositis, etc).
Video otoscopic examination
Video otoscopic examination has several advantages over using a standard handheld otoscope. The video otoscope has intense magnification which will allow you to visualize the ear canal and ear drum. In addition, images can be taken of lesions or problems within the ear.
Cultures are most commonly used when bacteria is present in a chronic otitis case. The yeast can be difficult to grow and should be readily found on your cytology. Bacterial cultures are usually not used for first time cases.
The results of the bacterial culture and sensitivity can be useful for helping to select the best systemic therapy. However, treatment choices for topical medications can be limited and the concentrations of drugs used topically are much greater than those used on the sensitivity discs. Therefore, a drug that is not as sensitive on a culture and sensitivity result may work well topically.
Radiographic imaging options
The three different radiographic imaging options that are available are bulla series radiographs, Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) All of these imaging options will require general anesthesia or heavy sedation. The owners need to be aware of this situation prior to performing any of these tests.
The least expensive and most readily option that is available in private practice are the bulla series radiographs. Proper positioning is vital to get useful radiographs to evaluate. Lateral, dorsoventral, or ventrodorsal, latero-20 degree ventral laterodorsal oblique and rostro 30 degree ventral-caudodorsal open-mouth oblique radiographs are recommended. The disadvantage is that contrast dye cannot help to visualize soft tissue lesions that might be present.
CT scans are one of the more common diagnostic imaging options used for otitis. This allows you to better visualize the pathology that is present in the bone and soft tissue. Boney involvement would be most likely with an osteomyelitis or a tumor that is lysing the bone. Any soft tissue abnormalities can be better enhanced by using contrast dye.
MRI is more costly than the CT scans. MRI is most beneficial for differentiating central versus peripheral vestibular disease. In addition, the MRI is known to have a more superior contrast resolution of soft tissue than CT scans.