Phaeoisaria sp. fungal keratitis resembling corneal rust residue: a case report

Abstract

Background

Fungal keratitis can develop after plant injury or after prolonged glucocorticoid use. Typical manifestations include corneal infiltrates, satellite lesions, plaques, and an immune ring. Some cases exhibit atypical signs, requiring reliance on etiological examination. Notably, fungi previously deemed nonpathogenic to humans can cause keratitis with rare clinical manifestations. This report details the clinical signs and successful treatment outcomes of keratitis caused by Phaeoisaria sp.

Case presentation

A 51-year-old man visited the ophthalmology clinic with ongoing eye pain and a history of corneal iron foreign body removal two months earlier. Examination revealed a brownish ulcer with clear borders, swelling, and redness, indicating the presence of rust. Although the initial cultures were negative, a rare fungus called Phaeoisaria sp. was eventually identified as causative agent. The patient completed six weeks of antifungal treatment and showed no signs of recurrence at the 7-month follow-up visit.

Conclusions

Patients with a history of corneal foreign bodies should also be informed of the possibility of atypical corneal fungal infection.

Background

Fungal keratitis often develops after plant-related injuries or prolonged glucocorticoid use. Common pathogens include Candida spp., Fusarium spp., and Aspergillus spp. [1]. Typical clinical manifestations include deep corneal infiltrates with feathery margins and raised surfaces, satellite lesions, endothelial plaques, a dry and rough texture, pigmentation, and an immune ring [2]. However, the clinical presentation of fungal keratitis is atypical, and there may be no obvious clinical symptoms in the early stages of infection. In addition, the time required for fungal pathogen diagnosis is longer than that required for bacterial infections.Consequently, these patients may be diagnosed at a later stage, which increases the risk of delayed antifungal treatment [2]. Notably, numerous fungi, previously considered nonpathogenic to humans, are frequently isolated as causative agents in keratitis cases, and their associated clinical manifestations may be quite rare. Only one case of fungal keratitis caused by Phaeoisaria clematidis has been reported, and the lesion has not been thoroughly described. Therefore, we present this case to emphasize the rare clinical manifestations and successful treatment outcomes of keratitis caused by Phaeoisaria sp.

Case presentation

A 51-year-old male presented to the ophthalmology clinic with persistent eye pain lasting for 19 days and a history of corneal iron foreign body removal two months earlier. Slit-lamp examination revealed a brownish ulcer with clear borders, corneal edema, and ciliary and conjunctival hyperemia. (Fig. 1) At the initial visit, samples for bacteria and fungal smears, as well as cultures from the base of the ulcer, were collected. Corneal scraping of the ulcer base revealed no organisms. The patient’s medical history, ocular findings, and the distinct appearance of the corneal ulcer led to the suspicion of rust deposition. However, the recurrence of a white, fluffy deposit with yellow and brown spots a week after the operation prompted further evaluation. Follow-up culture examination result revealed grey colonies with a significant presence of hyphae. The fungal culture identified the causative organism was recognized as a rather rare pathogen due to its numerous denticulate conidiogenous cells with lactophenol cotton blue stained at the end of branches [3]-- Phaeoisaria sp. (Fig. 2) A diagnosis of fungal keratitis was made. To identify the culture species, scraped corneal ulcer tissue was sequenced and analyzed using the Basic Local Alignment Search Tool (BLAST). This report revealed a high similarity with several strains of Phaeoisaria sp..

Fig. 1.

Clinical Characteristic (A) Clinical photograph of a brownish ulcer on the corneal surface at first visit. (B) Optical coherence tomography (OCT) reveals corneal ulcers are locally thinned and reflective are enhanced (C, D) IVCM reveals the presence of inflammatory cells and some suspicious fungal hyphae (marked by red arrows). (E) After scraping of the lesion 1 week, the recurrence of a white, fluffy appearance at the central lesion (F) OCT reveals the thickness of the corneal ulcers. (G, H) IVCM reveals more suspicious fungal hyphae (marked by red arrows) (I, J, K) Corneal epithelial repair and stromal scar formation after 4 months treatment

Fig. 2.

Laboratory examination. (A, B) Numerous fungal hyphae was found on corneal scraping smear (marked by black arrow); (C, D, E) The colonies appearance was gray in fungal culture; (F) Unstained morphology of the fungus in culture (400X); (G) The Medan staining morphology of the fungus in culture (400X); (H) Medan staining morphology of the fungus in culture (1000X)

The patient completed six weeks of antifungal therapy, using 0.1% amphotericin B eye drops every two hours followed by a gradual tapering. Additionally, an iodine tincture burn was performed on the corneal ulcer area, initially once every two weeks. Since the ulcer stabilized after treatment, the frequency was changed to once a week after one week. The iodine tincture treatment lasted for a total of two weeks. The lesions gradually shrank with scar formation after four weeks of treatment. No hyphae were detected using in vivo confocal microscopy (IVCM). At the seven-month follow-up visit, the patient remained asymptomatic with no signs of recurrence, indicating successful resolution of the infection.

Discussion and conclusions

The corneal lesion in our patient resulted from an iron foreign body injury, appearing brownish in color, which differed from the typical presentation of fungal keratitis, making it susceptible to misdiagnosis as rust residue. Post-traumatic keratitis has been reported in 55–65% of keratomycosis cases according to previous research [1]. Therefore, it is crucial to acknowledge the potential for fungal infection and remain vigilant.

Phaeoisaria sp. primarily causes plant infections, wheras human infections caused by this fungus are uncommon. Phaeoisaria clematidis mainly infects plants such as Clematis, and only one previous research has reported it as a cause of human keratitis. However, its clinical characteristics and the corneal ulcers have not been fully described [4]. Phaeoisaria sp. is a dark, filamentous fungus with low invasive potential and a high likelihood of lateral growth on the cornea [4]. While previous studies have focused on the etiology, this study pays more attention to the unusual appearance of corneal ulcers and their imaging features.

According to previous studies [3], this species of fungus is known for its high level of resistance, and is likely to be resistant to commonly used antifungal drugs in clinical practice. Given the severity of the patient’s condition, we administered 0.1% amphotericin B eye drops in combination with surgical intervention and the topical application of iodine tinctures. Removing red material from the surface of corneal ulcers provides specimens for pathogen detection and aids in the identification of ferrous foreign bodies. This may enhance the efficacy of topical drug therapy.

In our literature search, previous animal studies indicated that Phaeoisaria clematidis can infect mice, leading to dark nodular lesions across multiple organs. Histological examination revealed that the lesions were characterized by granulomata [5]. However, there is currently no direct evidence of human infection in other organs. Further research is necessary to explore the potential pathogenic mechanisms and clinical relevance of this fungus.

In this case, burn of corneal ulcer with iodine tincture is a traditional anti-infective treatment that is still used in developing countries. Clinical experience suggests that this treatment can shorten the course of fungal keratitis, but further studies are needed to confirm.

In conclusion, this case highlights the importance of considering corneal fungal infection in patients with corneal foreign bodies. Corneal smear and IVCM examination should be conducted for suspected cases with a history of trauma. Therefore, early detection, diagnosis, and treatment of this condition are crucial. Proactive use of antifungal drugs, smear and cauterization of corneal lesions, and applying iodine tincture can effectively manage disease progression.

Abbreviations

OCT

Optical coherence tomography

IVCM

In vivo confocal microscopy

Author contributions

Study Design: YingHan Zhao, MengYao Zhang, RongMei Peng; Data acquisition: YingHan Zhao, MengYao Zhang, Jing Hong, YingYu Li, Pei Zhang, RongMei Peng; Manuscript preparation: YingHan Zhao, MengYao Zhang, RongMei Peng. All authors reviewed the manuscript. All authors read and approved the final manuscript.

Funding

This study is supported by the National Natural Science Foundation of China (No. 81800801 and No. 31271045). The funding organization had no role in the design and conduct of this research.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Written informed consent was obtained from the patient for publication of this case report.

Competing interests

The authors declare no competing interests.