CNS disease occurs in about 20% of affected cats; CNS signs include depression, circling, seizures, ataxia, head pressing, paresis, behavior changes, and cranial nerve deficits. Hematogenous spread or invasion through the cribriform plate are possible routes of spread to the CNS.⁷ The cat in this case appeared normal on neurologic examination; however, its decreased appetite and activity level may have been manifestations of neurologic involvement.

Diagnosis

Definitive diagnosis is best obtained by organism identification either through cytologic or histologic examination of affected sites. Organisms are commonly found in nasal and skin exudates, nodule aspirates, cerebrospinal fluid, or subretinal or vitreous aspirates.⁷ A cytologic specimen is best examined using Gram's stain or new methylene blue stain. Wright's stain is also often used but can cause the organism to shrink, distorting the capsule.¹ Diff-Quik (Dade Behring) was used in this case. Cryptococcus neoformans can be cultured from exudates, cerebrospinal fluid, urine, joint fluid, or tissue samples if the sample is large enough. The organism grows readily on Sabouraud's dextrose agar, with yeast appearing in two days to six weeks.⁷

Prognosis

Cryptococcosis in cats without CNS or ocular disease typically has a favorable prognosis.⁸ Cases with only nasal or cutaneous involvement generally resolve with treatment.⁸ When extensive chorioretinitis is present, especially with concurrent retinal detachments, the prognosis for vision is poor. Secondary glaucoma can also develop.³

Treatment

Treatment for cryptococcosis with a triazole antifungal, such as fluconazole (50 mg/cat orally twice a day) or itraconazole (10 mg/kg orally once a day),⁷ is typically recommended for an average of eight and a half months, or at least for one or two months after clinical signs resolve.^1,8 Fluconazole is the most effective.⁷ But because itraconazole is dosed once a day, it may be preferred in cats that are difficult to medicate. Fluconazole has low protein binding and readily crosses the blood-brain barrier.⁵ Itraconazole has high protein binding and only develops low concentrations in the CNS; however, both fluconazole and itraconazole are effective for treating CNS disease.⁸ Because of its low protein binding, fluconazole also readily crosses the blood-aqueous and blood-retinal barriers, making it an ideal choice for ocular disease as well.¹⁰ Ketoconazole is not recommended because of its decreased efficacy and increased potential for adverse effects.⁷

Amphotericin B and flucytosine have synergistic effects against fungal organisms and appear to be useful in treating CNS disease. Flucytosine crosses the blood-brain barrier better than amphotericin B or ketoconazole.⁸ Flucytosine (25 to 50 mg/kg) is given orally four times daily.⁷ Amphotericin B (0.5 to 0.8 mg/kg) diluted in 400 ml of 0.45% saline solution containing 2.5% dextrose is administered subcutaneously two to three times weekly. Take care to properly dilute the amphotericin B because subcutaneous administration of more concentrated amphotericin B can lead to sterile abscess formation. Amphotericin B can also be used in conjunction with a triazole antifungal.⁷ Because of higher incidences of adverse effects, amphotericin B and flucytosine are recommended only in patients that fail to respond to azoles.⁸