A challenging case: Blindness and a history of cutaneous nodules in a cat - Veterinary Medicine
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A challenging case: Blindness and a history of cutaneous nodules in a cat
Ocular signs, a decreased appetite, and previous skin nodules were the only clues that this indoor-only cat had a life-threatening disease.


VETERINARY MEDICINE


DISCUSSION

Cryptococcosis is the most commonly diagnosed systemic mycosis in cats.1 The specific variety or serotype of Cryptococcus neoformans is rarely identified in affected patients in North America.2 Cryptococcus species can be found worldwide in temperate, tropical, and subtropical climates (cryptococcosis, unlike most fungal diseases, does not have a specific geographic distribution).1 Cryptococcus neoformans var neoformans is found in soil and pigeon excreta.3 Cryptococcus neoformans var gattii is associated with eucalyptus trees and had been considered a problem only in subtropical regions of Australia and South America. However, a recent retrospective study of an outbreak of cryptococcosis in a variety of animals in southwestern British Columbia reported that 13 of the 15 cultures obtained revealed C. neoformans var gattii.2

Pathogenesis

Unlike Blastomyces, Histoplasma, and Coccidioides species, which typically colonize the lungs first, Cryptococcus species initially colonize the nasal passages.4 Once inside the host, the cryptococcal organism regenerates its thick capsule, making it too large (5 to 20 μm) to enter smaller airways. Because of that, spread to the lower respiratory tract is rare.1 However, two retrospective studies in North America described three of six cats and six of nine cats, respectively, with cryptococcal invasion of lung tissue.2,5 Hematogenous or local spread to the central nervous system (CNS), skin, or eyes can also occur.1

In people, immunosuppression is a common predisposing factor in the development of cryptococcosis. In cats, immunosuppression secondary to FeLV and FIV infection has been suggested as a contributing factor in the development of cryptococcosis. However, one study reported the seroprevalence of FeLV and FIV in a population of Cryptococcus species-infected cats to be the same as or less than that of a normal population of cats.1 In a study evaluating the fungal flora on the skin and mucous membranes of 35 retroviral-infected cats and 50 FeLV- and FIV-seronegative cats, C. neoformans was isolated from only one cat that was asymptomatic and seronegative for retrovirus infection.6 It has been suggested that cats seropositive for FeLV and FIV infection are more severely affected by the disease and have poorer response to treatment.7

Because the cat in this case was previously vaccinated for FIV, testing for FIV would likely have yielded a positive antibody test and would have been of questionable value. However, antigen testing or FeLV testing would have been valuable for determining the prognosis in this case.

Typical clinical findings

Clinical signs are typically manifestations of nasal, cutaneous, ocular, or CNS involvement. Nonspecific signs including depression and anorexia leading to weight loss are common. Although the cat in this case presented with no upper respiratory signs, sneezing, snuffling, and nasal discharge occur in 50% to 80% of affected cats. The nasal discharge can be bilateral or unilateral and serous, mucopurulent, or hemorrhagic. Proliferative masses or ulcerated lesions of the nasal cavity can also occur.7

Skin lesions are present in about 40% to 50% of affected cats and include papules and nodules that may or may not become ulcerated or drain.1 The cat in this case had a history of nodular skin lesions. However, it is unclear if the lesions resulted from cryptococcosis because no organisms were found on histologic examination and the lesions resolved with antibiotics and low doses of glucocorticoids.

Ocular signs occur in about 20% to 25% of feline cryptococcosis cases and include chorioretinitis, optic neuritis, and anterior uveitis.7 Chorioretinitis, as seen in this case, is caused by the formation of pyogranulomatous lesions beneath the retina, which appear as poorly marginated grayish-white masses. Extensive exudate between the neurosensory retina and the retinal-pigmented epithelium can lead to retinal detachments and blindness.3


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Source: VETERINARY MEDICINE,
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