Clindamycin-Induced Black Hairy Tongue with Dermoscopic ‘Caterpillar-Like’ Appearance

A 56-year-old woman presented with a sudden onset of brown-black discolouration over the dorsal tongue following a 14-day course of oral clindamycin for a dental infection. Examination revealed elongated, brown to black filiform papillae predominantly affecting the midline and posterior tongue [Figure 1a]. Dermoscopy (DermLite DL4, polarised, ×10) demonstrated numerous elongated, pigmented papillae with tufted ends, imparting a ‘caterpillar-like’ appearance [Figure 1b]. A diagnosis of black hairy tongue (BHT) was made. BHT (lingua villosa nigra) is a benign disorder caused by impaired desquamation and hypertrophy of filiform papillae, leading to keratin retention and colonisation by chromogenic organisms. Risk factors include antibiotics, poor oral hygiene, smoking and xerostomia. In our patient, temporal association with clindamycin initiation and resolution on discontinuation strongly suggested drug-induced BHT. Using the Naranjo Adverse Drug Reaction Probability Scale, the score was 6, indicating a probable adverse drug reaction attributable to clindamycin. Management consists of withdrawal of the offending drug, reinforcement of oral hygiene and mechanical debridement with tongue brushing or scraping.^[1] The prognosis is excellent, with most cases resolving spontaneously within a few weeks. Clindamycin can rarely induce BHT. Dermoscopy may reveal a distinctive ‘caterpillar-like’ pattern, and causality can be supported by the Naranjo scale. Recognising this benign condition prevents unnecessary investigations and reassures patients.

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Figure 1:

(a) Clinical photograph showing brown-black elongation of filiform papillae over the dorsal tongue. (b) Dermoscopy (DermLite DL4, polarised, ×10) revealing elongated yellowish-brown to brownish-black filiform papillae arranged in parallel tufts resembling a caterpillar (green arrow). White globular foci over a pinkish mucosal background (red and black arrows) simulate rose petal-like structures. A characteristic gradient of pigmentation within single papillae is evident, with bases lighter than tips (blue arrow).

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