Black Hairy Tongue on Second Line Antituberculous Therapy: Don’t Forget Linezolid Induced Lingua Villosa Nigra

To the Editors: A 10-year-old boy was treated for abdominal tuberculous adenopathy in May 2023 at another hospital due to fever and abdominal pain for 1 month. Ultrasonography of the abdomen had shown necrotic mesenteric adenopathy. He received first-line antitubercular therapy (ATT) consisting of isoniazid, rifampicin, pyrazinamide and ethambutol for 2 months, followed by Isoniazid, Rifampicin, Ethambutol for 4 months. Other details are not available. In December 2024, he received first-line ATT for 3 months in view of fever and abdominal pain and computed tomography abdomen was suggestive of abdominal necrotic lymph nodes. The details of this treatment are also not available. In March 2025, he presented to us with intermittent fever and abdominal pain for 20 days. He weighed 26.5 kg (between 25th and 50th percentile as per the Indian Academy of Pediatrics growth charts). His heart rate was 107/min, and blood pressure was 82/48 mm Hg. Computed tomography chest showed ground-glass opacities in the posterior and superior segments of the left lower lobe of the lung, mild pericardial effusion, mediastinal and retroperitoneal necrotic lymphadenopathy, ascites and mild hepatosplenomegaly. Ultrasonography of the abdomen revealed enlarged periportal and left external iliac lymph nodes, a calcific granuloma in segment 7 of the liver and splenomegaly. A biopsy of abdominal lymph nodes was done and Xpert MTB/RIF ultra-detected Mycobacterium tuberculosis with indeterminate rifampicin resistance. He was started on second-line ATT with bedaquiline, delamanid, moxifloxacin, linezolid, cycloserine, clofazimine and steroids at 2 mg/kg/d in view of previous treatment failure with first-line ATT. At a 1-month follow-up, he developed a blackish discoloration of the tongue (Fig. 1). He was stable vitally, and blood chemistry and blood counts were normal. He also did not have any history of consuming coffee, tea or other colored beverages or using mouthwash. The discoloration was asymptomatic, did not cause pain or interfere with feeding or taste, and would reappear after brushing. The clinical appearance was consistent with black hairy tongue (BHT), a rare cosmetic side effect of linezolid. Linezolid was discontinued, and the discoloration disappeared within 10 days (Fig. 1B). The rest of the ATT regimen was continued along with gradual tapering of steroids.FIGURE 1.: A: Blackish discoloration of the tongue with a child on linezolid. B: Resolution of blackish discoloration on stopping linezolid.Linezolid, a crucial drug for drug-resistant tuberculosis, is associated with a benign side effect of BHT.1,2 BHT is believed to result from defective desquamation of the tongue, leading to hypertrophy and elongation of the filiform papillae, which then become stained by chromogenic bacteria or other exogenous agents. This usually gives a black carpet-like stain over the tongue; however could also rarely present as yellow, brown, green or blue discoloration.3 Some of the known risk factors include smoking, excessive coffee or tea intake, oxidizing mouthwashes, poor oral hygiene and certain medications like penicillin, neomycin, antipsychotics or erythromycin. Amongst the drugs used for ATT, linezolid is the most implicated.4 Linezolid, an oxazolidinone antibiotic, a protein synthesis inhibitor, targets the initiation complex and has been occasionally implicated with skin and soft tissue infections with an incidence of 0.2%.3,4 Though usually asymptomatic, BHT may present with halitosis, altered taste or nausea.1 This condition is benign and self-limiting. The diagnosis of BHT relies on a visual examination. Microscopic findings may show the characteristic changes in papilla; however is not implicated to make a definitive diagnosis.3 Because this condition is benign, over-investigation and treatment should be avoided and patients should be reassured, as it can be aesthetically disturbing.1 In drug-induced cases such as ours, cessation of the offending agent and maintenance of good oral hygiene typically result in full resolution. Sometimes, gentle debridement with a toothbrush as well as rinsing with baking soda or 3% hydrogen peroxide, may help with desquamation of the tongue.3 Prompt recognition of this rare adverse effect is essential to prevent unnecessary alarm or intervention. Increased clinician awareness will aid in timely diagnosis and reassurance of patients and caregivers. Our patient showed complete resolution after 10 days of stopping linezolid.