【摘要】 We report successful treatment of a case of fungal keratitis caused by Pseudallescheria boydii with minimal corneal scar. A 71yearold woman with history of pain, redness and foreign body sensation presented to our tertiary eye center. Initial corneal scraping revealed fungal elements. After two days fungal culture became positive, and after five days it was shown to be growth of Pseudallescheria boydii. The patient achieved clinical cures with medical therapy alone with minimal corneal scar and good visual outcome of 3/10.
【关键词】 fungal keratitis pseudallescheria boydii scedosporium apiospermum
INTRODUCTION
Filamentous fungus Pseudallescheria boydii is one of the rare causes of keratitis. Case histories appeared in literature vary from successful treatment with topical antifungals to complete loss of vision secondary to overwhelming infection. We hereby report a case of Pseudallescheria boydii keratitis that was successfully managed with medical therapy leading to favorable outcome with minimal corneal scar.
CASE REPORT
A 71yearold woman without significant past ocular pathology suffered from minor trauma in her left eye with organic matter while working at her garden. Due to pain and redness, several days after trauma she was referred to the local emergency room and was treated with a variety of topical antiinfectives including chloramphenicol and ciprofloxacin, but without improvement. Two weeks after initial presentation she was referred to our emergency clinic for treatment.
At presentation her left visual acuity was light perception. Slitlamp examination of the affected eye revealed a 6mm×5mm central stromal infiltration with a corresponding epithelial defect but no stromal thinning and perforation (Figure 1). No hypopyon was present. Corneal scraping at the time of admission was positive for fungal elements and no bacterial organism was found. Culture was subsequently positive for Pseudallescheria boydii (Figure 2). Initial treatment consisted of hourly topical natamycin 5g/L and oral ketoconazole 200mg twice daily. Epithelial debridement was also performed several times during hospital course.
Following very gradual improvement in stromal infiltration and decrease in associated epithelial defect, she was discharged after two weeks with slow tapering of topical natamycin and discontinuation of ketoconazole over the next six weeks. The patient remained free of recurrence at her 3month followup visit with best corrected visual acuity of 3/10, with mild central corneal scar and haziness and mild lens nuclear sclerosis (Figure 3).
DISCUSSION
Fungal keratitis despite its uncommon incidence must be considered in all cases of traumatic exposure to organic matter and failure of improvement following conventional antibacterial regimen[1,2].
The gold standard for diagnosis of fungal keratitis is visualization of fungal elements in corneal tissue, whereas cultures may be misleading secondary to contamination of media due to ubiquitous nature of fungi[3]. In vitro susceptibility testing of a particular isolate is of limited value due to contrasting evidence in the literature[46]. In addition, by the time results are obtained, the clinical appearance of keratitis will determine whether it is responding to medical treatment or surgery is indicated.
It is appropriate to begin empirical antifungal therapy and preclude the use of corticosteroid at the first suspicion of fungal etiology even before confirmatory cultures[3]. Even with appropriate therapy fungal pathogen in the cornea can be difficult to eradicate and can lead to prolonged treatment course. In cases of medical treatment failure, penetrating keratoplasty may be necessary.
Scedosporium apiospermum is the asexual state of Pseudallescheria boydii. Both sexual and asexual forms are rare causes of fungal keratitis, mostly appeared in literature as isolated case reports[712]. It has also been reported as a cause of fungal keratitis following laser in situ keratomileusis, which lends special prominence to this fungus[13,14]. This organism has a tendency to progress to fulminant endophthalmitis, hence requiring early diagnosis and aggressive therapy[10,15,16].
Figure 1 Slitlamp examination showing a 6mm×5mm central stromal infiltration with a corresponding epithelial defect(略)
Figure 2 Photomicrograph showing Pseudallescheria boydii hyphae(略)
Figure 3 Three months after treatment only mild central corneal scar and haziness and mild lens nuclear sclerosis could be seen(略)
Fungal keratitis secondary to Pseudallescheria boydii has various outcomes, which vary from successful treatment with topical antifungals[14,17] to complete loss of vision secondary to overwhelming infection[10,14]. Unfortunately in many cases of Pseudallescheria boydii keratitis, topical steroids were used in the early therapeutic regimen, and this can exacerbate the infection and increase the likelihood that the keratitis evolves into overwhelming eye infection, and finally enucleation has to be done.
Recently, Wu et al[14] have reviewed data of all reported cases of Pseudallescheria boydii keratitis in literature. Their review clearly shows the unpredictability of this microorganism to treatment options. They concluded that fungal keratitis due to this fungus should be treated aggressively, and miconazole should be an important part of therapeutic regimen. The azoles including miconazole[11,17], ketoconazole[12,13], and fluconazole[14] have been used successfully to treat Pseudallescheria boydii keratitis and are considered the agents of choice. Voriconazole, a new derivative of fluconazole, has shown high in vitro and in vivo potency against Scedosporium apiospermum[18,19], although it has not been used for such type of keratitis. Ketoconazole is the most frequently used oral antifungal agent in management of fungal keratitis. Natamycin, a polyene compound, is still considered the initial drug of choice in fungal keratitis. In addition, debridement of corneal epithelium is an essential component of fungal keratitis, especially early in the course of treatment[20].
Our good result in this case is most probably due to avoidance of topical steroid use in the early management of keratitis before confirmatory scraping and culture became available. Another possible mechanism is repeated corneal debridement early in the course of medical management. Debridement works by debulking organisms and necrotic materials and by enhancing the penetration of the topical antifungal to better access the deeper corneal layers to eradicate the infection[20].
Finally, this case clearly shows that avoidance of using topical corticosteroid in suspicious cases of fungal keratitis in conjunction with diagnostic corneal scraping and aggressive antifungal therapy can lead to good visual outcome and prevent devastating complications.
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