Background:

Prototheca spp. are rare human pathogens, and only three cases of Prototheca keratitis have been reported. They were treated with anti-fungal drugs and surgical excision. Two of the three cases were successful, and the case of an immunocompromised patient was not successful. Thus, the best treatment of Prototheca keratitis is still undetermined, and further investigations are needed. The purpose of this report is to present our findings in a case of Prototheca keratitis that was successfully treated with topical medications without surgical excision.
Methods:
This study was performed in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of Hidaka Medical Center, Toyooka Hospital. A written informed consent was obtained from the patient before beginning the medical treatments.
Case report:
A 75-year-old man with a history of stage 4 prostate carcinoma and bilateral limbal stem cell deficiency had undergone keratoepithelioplasty on his left eye for the deficiency. Postoperatively, a greyish-white epithelial opacity was noted on the central cornea of his left eye, and he had been treated with topical fluorometholone and oral dexamethasone together with a therapeutic contact lens. Corneal smears and contact lens swabs were positive for Prototheca spp. He required a continuous treatment with amphotericin B (AMPH-B) ointment, topical fluconazole (FLCZ), and voriconazole (VRCZ). This treatment protocol was effective, but recurrences developed when his general condition worsened.
Conclusion:
Our findings indicate that Prototheca keratitis can be successfully treated but not cured with topical AMPH-B, FLCZ, and VRCZ without surgical treatment. However, recurrences can develop when the general condition of the patient worsens. Thus, continuous monitoring and treatment are necessary in cases of Prototheca keratitis.