A 13-year old neutered male DSH cat presents with inspiratory dyspnoea, frequent sneezing, congestion, weight loss and partial anorexia of three months’ duration. Physical examination reveals bilateral mucopurulent nasal discharge. Amoxicillin/clavulanic acid has been administered unsuccessfully. Vaccinations are up-to-date and the cat is free roaming. A smear is prepared from a nasal flush (Wright’s, ×40). Cranial radiographs do not reveal any osteolytic lesions or evidence of a mass.
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What is your diagnosis based on cytological observation?
The microphotograph illustrates a hyphal structure compatible with Aspergillus species. Nasal aspergillosis is therefore the likely diagnosis.
This infection is more common in dogs than in cats, particularly long-nosed breeds (e.g. Collies).
What other diagnostic tests can be performed to support this diagnosis?
Rhinoscopy can reveal atrophy of turbinates and the presence of white or grey plaques.
Histological examination, like cytology, can demonstrate fungal hyphae; these are nonpigmented, segmented and branching structures; fungal culture can be performed on material obtained from a nasal flush or tissue sampling during rhinoscopy.
Serology for detection of antibodies against Aspergillus species is a complementary diagnostic tool but less useful, as false positives do occur. A positive test supports prior exposure to the organism but does not confirm current infection. A negative antibody test does not rule out the possibility of Aspergillus infection.
Radiographic examination may reveal nonspecific osteolytic lesions that may also be observed with neoplasia.
It should be noted that for cytological examination, material obtained via a nasal flush or biopsy is preferred to nasal secretions, which may not contain the organism.
Oral fluconazole or itraconazole can be administered; topical infusion of an antifungal drug such as clotrimazole has been shown to be effective in dogs, and may clear infections more successfully than systemic therapy.
Note: Aspergillus organisms in cytological preparations are usually observed as uniform, septate hyphae of 3–6 microns in width with 45-degree angle (dichotomous) branching.
A differential diagnosis is phycomycosis, but these fungi are rarely septate. The presence of septate, branching hyphae in a nasal cytological preparation is strongly supportive of aspergillosis.
Definitive diagnosis is by evaluation of reproductive structures, which are seldom seen in cytological specimens but can be identified in preparations of fungal cultures.
Nasal flushings can be very frustrating because they may reflect nonspecific inflammation and may not contain diagnostic features. Client education regarding the possibility of a nonrepresentative specimen and the possible need to progress to nasal biopsy is recommended.
Nasal biopsy specimens taken from multiple locations may be needed and aggressive sampling is recommended to obtain specimens that will give the clinician and pathologist confidence in making a diagnosis.
