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Vol. 25. Issue 5.
(September - October 2021)
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Vol. 25. Issue 5.
(September - October 2021)
Clinical Image
Open Access
Black hairy tongue caused by metronidazole
Yu Niiyamaa,b, Ryota Hasea,b,
Corresponding author

Corresponding author at: Department of Infectious Diseases, Japanese Red Cross Narita Hospital, Narita, Chiba, Japan.
a Department of Infectious Diseases, Japanese Red Cross Narita Hospital, Narita, Chiba, Japan
b Department of Infectious Diseases, Kameda Medical Center, Kamogawa, Chiba, Japan
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An 82-year-old woman complained of fever, headache, and left hemiplegia. She has past medical histories of hypertension and brain infarction. CT scan revealed brain abscess. Hence, she underwent surgical drainage and antimicrobial treatment with ceftriaxone and metronidazole. On hospital day 28, she manifested anorexia and nausea, with black discoloration of her tongue (Fig. 1A). We suspected antibiotic-induced black hairy tongue (BHT) and thereby discontinued metronidazole. Within two weeks, her anorexia, nausea, and the black discoloration of her tongue gradually improved (Fig. 1B). Therefore, she was diagnosed with BHT due to metronidazole.

Fig. 1.

(A) Black hair-like lesion appeared on the dorsal aspect of the patient's tongue 28 days after starting metronidazole treatment. (B) Both black discoloration and hair-like appearance on the patient's tongue were improved 14 days after discontinuing metronidazole treatment.


BHT is a benign condition characterized by hypertrophy and lengthening of the filiform papilla on the dorsal aspect of the tongue. The hair-like appearance of BHT results from the inadequate desquamation of keratin over the filiform papillae; meanwhile, its discoloration results from the presence of porphyrin-producing chromogenic bacteria or yeast, with black to blackish-brown as the most common discoloration.1 Moreover, BHT is linked to various behavioral factors, such as smoking and poor oral hygiene, and the use of several medications, including antibiotics. Erythromycin, doxycycline, linezolid, penicillin, minocycline, and metronidazole reportedly cause BHT.2 Generally, BHT is managed by discontinuing the potential causative medication, modifying the predisposing factors, maintaining a good oral hygiene with tongue care to promote desquamation of the hyperkeratotic papillae.3

Patient consent for publication: Written informed consent was obtained.

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Copyright © 2021. Sociedade Brasileira de Infectologia
The Brazilian Journal of Infectious Diseases

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