Black Hairy Tongue as a Rare Adverse Effect of Linezolid in Multidrug-Resistant Tuberculosis: A Case Report

Black hairy tongue (BHT), or lingua villosa nigra, is a rare adverse effect of linezolid, an antibiotic frequently used in the treatment of multidrug-resistant tuberculosis (MDR-TB). We present a case of a 24-year-old female who developed BHT while receiving linezolid as part of a longer regimen for MDR-TB. The patient exhibited a typical BHT presentation, with painless brown-to-black discoloration on the posterior dorsal surface of her tongue, appearing 25 days after initiating linezolid therapy. There were no other identifiable contributing factors. Upon discontinuation of linezolid and a shift to a modified regimen, the BHT completely resolved within 10 days. A Naranjo Adverse Drug Reaction Probability Scale score of 5 suggested a probable causal relationship between linezolid and BHT. This report represents the first documented case of linezolid-associated BHT from Nepal, highlighting the importance of clinicians' awareness of this rare but clinically significant side effect, especially within the context of MDR-TB treatment, to provide prompt diagnosis, reassurance, and appropriate management.