Protothecosis in the mucosa of the pharynx mimicking pharyngeal cancer in an immunocompetent individual: a case report

Marie Yamashita, Mahoko Ikeda, Ito Kato, Yuki Ohama, Mizuo Ando, Masako Ikemura, Daisuke Jubishi, Yoshiaki Kanno, Koh Okamoto, Takashi Umeyama, Shigeki Nakamura, Yoshitsugu Miyazaki, Shu Okugawa, Kyoji Moriya

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


Background: Protothecosis is a rare infection in humans and animals caused by the achlorophyllic algae Prototheca species. More than half of the protothecosis cases are cutaneous infections, and most cases are observed in immunocompromised individuals. Case presentation: We report a case of Prototheca wickerhamii infection in the mucosa of the pharynx in a 53-year-old immunocompetent woman with an incidentally found mass lesion at the left tongue base. Histopathological findings of the mass lesion suggested cryptococcosis, but P. wickerhamii was identified from the oropharynx scrape culture based on DNA sequencing. After surgical resection, fosfluconazole treatment was initiated, and subsequently, treatment was switched to topical amphotericin B. The residual mass lesion did not deteriorate during the 4-month antifungal treatment and 1-year observational period. Conclusions: Prototheca species can be easily misdiagnosed as yeasts because of their morphological and pathological similarities. Prototheca, in addition to Cryptococcus should be considered if slow-growing, large Gram-positive organisms are encountered. Lactophenol cotton blue staining of the colony helps distinguish these organisms. Further study is needed to determine the appropriate treatment according to the infection focus.

Original languageEnglish
Article number5
JournalAnnals of Clinical Microbiology and Antimicrobials
Issue number1
Publication statusPublished - Dec 2022
Externally publishedYes


  • Cryptococcus
  • Larynx
  • Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry
  • Prototheca wickerhamii
  • Protothecosis

ASJC Scopus subject areas

  • Microbiology (medical)
  • Infectious Diseases


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