Use of Posaconazole in the Management of Invasive Orbital Aspergillosis in a Cat

Introduction

Important differential considerations in cats with exophthalmos include orbital neoplasia, cellulitis/abscess, and foreign bodies.^1–6 Idiopathic inflammatory conditions are rare causes of exophthalmos in cats. Such conditions include orbital pseudotumor; a noninfectious, granulomatous, fibroproliferative disorder; eosinophilic infiltrates; and disorders of the infraorbital salivary gland, such as salivary mucocele.^7–9

Deep mycotic infections are uncommon in cats. In one published retrospective study, Cryptococcus neoformans was the most frequent cause of deep mycosis in cats, accounting for 263 of the 571 cases reported, whereas Aspergillus spp. infections accounted for only 40 (7%) of the cases.¹⁰ Cryptococcosis may be associated with a variety of ocular abnormalities, such as orbital disease (albeit infrequently).^11,12 Previous reports of filamentous fungal infection causing exophthalmos in cats are sparse.^2,13–16 Organisms isolated from affected cats have included Aspergillus and Penicillium species.^2,13–16 Two distinct forms of invasive aspergillosis are recognized in cats. Disseminated disease and nasal/frontal sinus infection both carry a guarded prognosis.^10,17,18 In previous reports, euthanasia of affected cats was frequently the outcome.^2,13–16 A feline case of orbital and nasal infection with the Oomycete, Pythium insidiosum, was successfully treated with itraconazole.¹⁹ The purpose of this report is to document a rare case of invasive orbital aspergillosis in a cat and the successful treatment with a novel triazole antifungal agent, posaconazole.

Case Report

A 4-year-old, castrated male Persian was referred for evaluation of progressive protrusion of the left third eyelid and serous ocular discharge of 2 months’ duration. Previous therapy consisted of topical chlortetracycline and antibiotic-corticosteroid ophthalmic ointments. The cat lived indoors, with supervised access to the outdoors. There was no history of trauma or previous respiratory or ocular disease. The cat was active and had a good appetite.

The left eye was moderately exophthalmic, with dorsal deviation of the globe and pronounced resistance to retropulsion. The conjunctiva of the left eye was moderately hyperemic, and the third eyelid was prominent, hyperemic, and slightly thickened [Figure 1]. Globe motility was reduced. Moderate restriction of forced ductions of the left eye in all directions was noted. No signs of discomfort were evident on globe retropulsion, palpation of the orbital rim, or opening of the mouth. Examination of the oral cavity revealed slight swelling of the oral mucosa in the left pterygopalatine fossa. Moderate epiphora was noted in the left eye. No significant lagophthalmos or corneal or other anterior segment lesions were noted in either eye, and menace responses and pupillary light reflexes were normal. Indirect ophthalmoscopy revealed no significant fundus abnormalities. Intraocular pressures, measured by applanation tonometry,^a were 14 and 23 mm Hg in the right and left eyes, respectively. Physical examination findings were otherwise normal, and the cat was afebrile.

Results of serum biochemical analysis and routine urinalysis were unremarkable, except for moderate hyperglobulinemia (6.6 g/dL; reference range 2.1 to 3.5 g/dL). A complete blood count (CBC) revealed moderate lymphopenia (0.572 × 10³/μL; reference range 1.5 to 7.0 × 10³/μL) and eosinophilia (1.048 × 10³/μL; reference range 0 to 0.75 × 10³/μL). Serological testing for feline leukemia virus (FeLV) antigen and feline immunodeficiency virus (FIV) antibody^b proved negative. Ultrasonography revealed slight indentation of the left globe by an ill-defined, mass lesion of mixed echogenicity located inferior-medially within the left orbit, outside the extraocular muscle cone. The cat was anesthetized, and transconjunctival fine-needle aspirates for cytological evaluation were obtained under ultrasound guidance. Aspirates were nondiagnostic because of low cellularity and blood contamination.

Computerized tomography (CT) demonstrated a soft-tissue mass inferior-medially within the left orbit. The lesion caused indentation and dorsal displacement of the globe [Figure 2] and extended caudally from the apex of the left upper canine tooth root to the region of the cribriform plate. A mild increase in soft-tissue density was seen within the left frontal sinus. No bony lesions or nasal cavity involvement were detected. A CT-guided aspirate of the mass lesion was performed, and cytological evaluation revealed moderate cellularity with 30% eosinophils, 30% neutrophils, 20% activated macrophages, and lesser numbers of lymphocytes, plasma cells, and mast cells. These cytological findings were suggestive of eosinophilic and pyogranulomatous inflammation, but no underlying infectious agents or evidence of neoplasia were identified. An additional aspirate, intended for microbial culture, was inadvertently discarded.

Thoracic radiographs were unremarkable, and serological testing for Cryptococcus neoformans antigen^c was negative. Serological tests for other invasive mycoses, such as histoplasmosis and aspergillosis, were not pursued because of the absence of systemic signs.^18,20 Exploratory orbitotomy was declined by the owner.

A provisional diagnosis of a retrobulbar eosinophilic infiltrate was made, and therapy was instituted with prednisone^d (1 mg/kg per os [PO] q 12 hours), amoxicillin-clavulanate^e (15 mg/kg PO q 12 hours), and neomycin-polymyxin B-bacitracin ophthalmic ointment^f (q 6 hours in the left eye). The cat was reevaluated after 10 days, and no improvement was noted. The possibility of an underlying orbital neoplasm, foreign body, or infectious process had not been definitively excluded; therefore, oral prednisone therapy was stopped, and surgical exploration of the orbit was recommended.

A modified lateral orbitotomy was performed via osteotomy of the left zygomatic arch.²¹ Multiple nodular, firm, pale-yellow masses were identified within the medial and inferior orbital tissues. The mass lesions were extensive and involved the medial pterygoid and extraocular muscles. A decision was made to exenterate the left globe and orbital contents, because the lesions were firmly adhered to the globe. The bony medial wall of the orbit was intact, but abnormal, pale nodular tissue extended posteriorly to the orbital apex in the region of the optic canal and orbital fissure. This tissue could not be fully excised. Excised tissues were submitted for bacterial and fungal culture and for histopathological evaluation. A single subcutaneous (SC) injection of ketoprofen^g (1 mg/kg) was administered, followed by aspirin^h (10 mg/kg PO q 48 hours) to relieve postoperative inflammation and pain. Cephalexinⁱ (20 mg/kg PO q 12 hours) was administered for 7 days. One day postoperatively, the cat was alert, eating normally, and was discharged from the hospital.

Histopathological evaluation of the orbital lesions identified foci of necrotic collagen and outlines of cells, each surrounded by a distinct zone of eosinophils, macrophages, and lymphocytes. Within these lesions, numerous small, branching, septate fungal hyphae were observed [Figure 3]. Similar changes were identified in the tissues of the third eyelid, but no abnormalities were detected within the left globe. Bacterial culture yielded no aerobic or anaerobic growth after 6 days. A moderate growth of Aspergillus fumigatus was obtained on fungal culture. The isolate was identified on the basis of culture morphology and the presence of characteristic conidia and conidiophores by light microscopy of lactophenol cotton blue-stained preparations. Antifungal susceptibility testing was not possible, as the original Aspergillus isolate failed to grow on subculture.

Because surgical excision of the orbital lesions was incomplete, systemic antifungal therapy was instituted with itraconazole^j (10 mg/kg PO q 24 hours). After 2 weeks of itraconazole therapy, the cat was sneezing, had left-sided mucopurulent nasal discharge, and moderate enlargement of the left submandibular lymph node. Palpation of the exenterated left orbit was unremarkable. The cat was anesthetized for a follow-up CT examination. A further increase in soft-tissue density within the left frontal sinus and nasal cavity was considered suspicious for fungal sinusitis/rhinitis. Trephination of the left frontal sinus was performed using a Steinmann pin and rongeurs, and 4 mL of clotrimazole^k (500 mg/mL suspension in polyethylene glycol-400) was instilled into the frontal sinus for 45 minutes after first removing a profuse, clear, thick, tenacious mucoid material from the sinus cavity. This material was acellular, and no infectious agents were identified on fungal and bacterial cultures. No other significant abnormalities were noted within the frontal sinus.

After an additional 4 weeks of oral itraconazole therapy, the cat was reevaluated for significant weight loss and difficulty in prehending and swallowing food. Firm swelling of the left facial region and upper lip was apparent, and signs of discomfort upon opening of the mouth were detected. Examination of the oral cavity revealed granulomatous, caseous lesions in the oral mucosa of the left palatine region and adjacent to the left upper canine and caudal upper molar teeth [Figure 4]. The cat was anesthetized, and a 5-mm wedge biopsy was obtained from a granulomatous lesion posterior to the caudal left upper molar tooth. Fungal culture of this tissue yielded growth of Aspergillus fumigatus.

Pending the results of subsequent antifungal susceptibility testing,^l oral itraconazole therapy was discontinued, and therapy was instituted with amphotericin B^m (0.8 mg/kg SC in 400 mL of warmed 2.5% dextrose/0.45% saline q 3 to 4 days). Serum urea and creatinine concentrations were measured, and a urinalysis was performed on a weekly basis. This treatment protocol was well tolerated, with only transient discomfort noted with the administration of large volumes of SC fluid. No biochemical evidence of nephrotoxicity or microscopic evidence of urinary tubular casts was identified during the 4 weeks of therapy. No clinical improvement was noted, however, and progressive weight loss and enlargement of the facial and oral lesions continued. Results of antifungal susceptibility testing on the Aspergillus fumigatus isolate [see Table] showed poor in vitro susceptibility to both itraconazole and amphotericin B. Of the four antifungal agents tested, the isolate was highly susceptible only to the triazole, posaconazole.

Amphotericin B therapy was discontinued, and therapy was instituted with posaconazole in a 40 mg/mL oral suspensionⁿ (5 mg/kg PO q 24 hours, with food). Monitoring of CBCs and serum biochemical profiles was continued every 2 weeks, with no significant abnormalities noted throughout the treatment period. The only potential adverse reactions noted were erythema and pruritus of the pinnae and superficial excoriation of the skin in the left temporal region from self-trauma associated with rubbing. Within 3 weeks, the submandibular lymphadenopathy had resolved, the granulomatous lesions in the oral cavity were dramatically smaller, and the cat had gained weight. By 10 weeks, only small, 1-to 2-mm fistulae remained in the oral mucosa at the sites of the previous granulomatous inflammation. Follow-up CT revealed resolution of soft-tissue density of the left frontal sinus, orbit, and nasal cavity. No destructive bony lesions were identified, although mild hyperostosis was noted in the region of the previous zygomatic osteotomy. The remaining oral lesions were healed completely within 12 weeks of initiating posaconazole therapy, and the cat’s body weight had increased by 2.7 kg. Posaconazole was discontinued after a total of 16 weeks. No signs of recurrence of infection have been noted in the subsequent 20 months.

Discussion

Invasive aspergillosis is a relatively uncommon but serious cause of orbital disease in humans and is usually encountered in immunocompromised individuals.^22–24 Although deep mycotic infections in cats may be associated with immunosuppressive conditions (e.g., previous corticosteroid administration or infection with FeLV, FIV, or feline panleukopenia virus), these have not been consistent features of previously reported feline sinus or orbital infections with filamentous fungi.^{10,13,14,17,18} Serological tests for FeLV and FIV infections were negative in the cat reported here. Moderate lymphopenia was identified at initial presentation, but studies of lymphocyte proliferation and function were not pursued. A prior report suggested that Persian cats may be predisposed to the development of invasive and disseminated aspergillosis.¹⁰

In previously reported cases of exophthalmos related to filamentous fungal infections in cats, orbital disease was generally suspected to have resulted from extension of a primary infection from the nasal cavity or paranasal sinuses.^13,14,16 Similarly, in humans, invasive orbital aspergillosis usually arises from the paranasal sinuses following inhalation.^22,23 In the case reported here, primary nasal cavity or sinus involvement was not supported by either the initial clinical presentation or the results of culture and cytology of sinus exudates. Aspergillus fumigatus is a saprophytic fungus that is ubiquitous in the environment, and it may be part of the normal commensal flora of the skin, conjunctival sac, and other mucosal surfaces.^25,26 How the fungus initially gained entry to the orbit was not determined, but the invasion may have incited an intense inflammatory response that failed to eliminate the organism and may have facilitated its spread within the orbital tissues.²⁷

The typical presentation in humans with orbital aspergillosis is painful exophthalmos and a fulminant, potentially fatal disease.^22–24 Invasive disease, with progressive granulomatous inflammation and fibrosis, may also be recognized.^22–24 In contrast, cats with orbital infections involving filamentous fungi have typically been presented with more gradually progressive, relatively nonpainful exophthalmos.^14,16 This more insidious presentation may lead to a delay in diagnosis and appropriate therapy. Fine-needle aspiration biopsy may be of value in the cytological diagnosis of orbital disease.^28,29 However, limitations of this diagnostic technique are illustrated by the failure to identify the relatively localized fungal hyphae in this case, with consequent delay in diagnosis and appropriate treatment of the orbital aspergillosis. In this case, initial therapy with corticosteroids may have enhanced the fungal infection. An apparent association between the development of disseminated, invasive aspergillosis in cats and prior administration of antibiotic and anti-inflammatory therapy has been documented.¹⁷ Corticosteroids may impair immune function and thereby inhibit leukocyte-mediated damage to fungal hyphae and the anti-conidial activity of macrophages.²³ In addition, corticosteroid exposure has resulted in a significant increase in the in vitro growth rate of Aspergillus fumigatus.³⁰

The triazole antifungal agent, itraconazole, was initially selected in this cat because of its documented efficacy against a variety of deep mycotic infections in cats and its relative safety in this species.^12,31,32 Itraconazole generally has good in vitro activity against Aspergillus spp., and itraconazole-resistant strains are uncommon.³³ Amphotericin B, a polyene antifungal agent, has similar or superior activity to itraconazole against Aspergillus spp. in vitro, and it has traditionally been considered the first-line therapy in humans with invasive orbital aspergillosis.^22,23 The potential for renal toxicity and the requirement for parenteral administration initially led to a reluctance to employ this agent in the cat reported here. While lipid formulations of amphotericin B may be less toxic, their cost was considered prohibitive.³⁴ In a published report of dogs and cats with cryptococcosis, nephrotoxicity was minimized by SC administration of the drug in a large volume of fluid, by slowing drug absorption, avoiding high peak blood concentrations, and promoting mild diuresis.³⁵ In the current case, no signs of nephrotoxicity related to amphotericin B were noted throughout the 4-week treatment period.

It is uncertain whether the initial therapeutic failure in this cat was related to intrinsic resistance or whether suboptimal pharmacokinetics or host factors also contributed. Prior itraconazole therapy has been implicated in the development of resistance to amphotericin B by Aspergillus isolates from humans.^33,36 Complete surgical excision of affected tissues was not achieved in this cat. Tissue penetration by both drugs may have been inadequate to achieve effective tissue concentrations, as the residual fungal hyphae were sequestered by the surrounding necrosis and granulomatous inflammatory response. It is difficult to correlate the in vitro minimal inhibitory concentration (MIC) of antifungal agents with in vivo efficacy, as numerous host factors (including the patient’s immune status) play a role in determining clinical outcome.³³

Posaconazole, a broad-spectrum triazole presently in phase III clinical trials in human patients, was selected in this case because of in vitro susceptibility testing. Posaconazole is often fungicidal and has promising activity against many yeasts and dimorphic and filamentous fungi such as Aspergillus spp., both in vitro and in rabbit and murine models of invasive aspergillosis.^37–41 The drug has a long half-life and good tissue distribution in a number of animal species.⁴² As no pharmacokinetic or toxicity data for the drug are available in cats, the treatment regimen selected for this cat was based on data from other species (i.e., rodents, rabbits, dogs, and monkeys).⁴² A single daily dose of posaconazole was administered with food, as pharmacokinetic studies in dogs demonstrated a significant effect of concurrent feeding on oral bioavailability.⁴² While cross-resistance has been noted between azoles in vitro, posaconazole appears to have the greatest activity in vitro against itraconazole-resistant isolates of Aspergillus fumigatus.^33,43,44

Conclusion

A 4-year-old Persian cat that was presented with unilateral exophthalmos was diagnosed with orbital aspergillosis. A favorable clinical outcome was achieved in this cat with posaconazole, after initial therapies with itraconazole and amphotericin B failed. On the basis of this case report, further evaluation of the antifungal agent, posaconazole, is warranted to assess its value in the treatment of life-threatening, deep mycotic infections in small animals.

Acknowledgments

The authors are indebted to Drs. K. Miles and E. Riedesel for their interpretation of diagnostic images; to Dr. M. Shaver and the senior veterinary students who participated in the clinical management of this cat; to Drs. R. King and L. Fox for their constructive comments on this manuscript; and to Dr. M.G. Rinaldi of the University of Texas Health Science Center and Dr. J. Petruska of Schering Plough Corporation for their advice regarding the selection and administration of posaconazole.