Chapter 155 For cats with unilateral nasal discharge and loss of nasal airflow, fungal infection and neoplasia should be high on the differential list. Cytologic analysis of nasal discharge is occasionally diagnostic for cryptococcosis by detection of a large (~20- to 30-µm) clear capsule surrounding a 3- to 8-µm organism (Figure 155-1). Cryptococcal antigen latex agglutination serologic testing should also be performed in cats with a loss of nasal airflow, since detection of circulating cryptococcal polysaccharide capsular antigen indicates infection. The assay has a high sensitivity (96% to 98%) and specificity (97% to 100%) when a pronase step is included in the method (pronase degrades antibodies that bind to the capsular antigen) (Malik et al, 1996; Trivedi et al, 2011). Fungal culture of a nasal swab also is indicated to isolate organisms for subsequent identification of species, antifungal susceptibility, and molecular subtype at a mycology reference laboratory. Nasal culture should not be used as a single diagnostic test for cryptococcosis, since it is possible for the nasal cavities of cats to be transiently colonized by cryptococcal organisms and not infected (Duncan et al, 2005). Figure 155-1 Smear from a nasopharyngeal cryptococcal granuloma treated with modified Wright-Giemsa (Diff-Quik) stain. The organisms, including a single budding yeast, are surrounded by a large polysaccharide capsule. Figure 155-2 Transaxial contrast-enhanced computed tomographic scan for a cat with sino-orbital aspergillosis. There is a mass in the ventromedial orbit causing dorsolateral displacement of the globe as well as opacification of the left frontal sinus, left sphenoid sinus, and choanae. The mycotic granuloma in the orbit has spread to the paranasal soft tissues adjacent the maxilla. The pattern of contrast enhancement is heterogenous, with encapsulated areas of peripheral rim enhancement. Collecting nasal swab or biopsy specimens for bacterial culture in cats in which CRS is suspected is controversial. Potential pathogens are isolated from nasal samples from cats with chronic rhinitis more commonly than from those from healthy cats (Johnson et al, 2005), and culture results are sometimes helpful in guiding antibiotic therapy to control secondary bacterial rhinitis. It is unclear whether it is of clinical value to determine the type of inflammation present in CRS; however, histopathologic analysis is critical for ruling out neoplasia or fungal infection. In the cat with CRS, lymphoplasmacytic inflammation likely reflects the chronic nature of disease, whereas neutrophilic inflammation indicates an acute or bacterial component to the disease process. Eosinophilic infiltrates are relatively uncommon, but this finding might be considered suggestive of herpesvirus infection, as has been found in FHV-1–related facial dermatitis (Hargis et al, 1999). Since eosinophilic infiltrates can also occur in fungal rhinitis, special stains to detect fungal elements (e.g., periodic acid–Schiff or Gomori’s methenamine silver) should be used.
Rhinitis in Cats
Diagnosis
Rhinitis in Cats
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