An 85-year old male cigar smoker with no notable medical history presented with black discoloration and hairy appearance ofthe tongue, which had lasted several years. He said he did not use bismuth- containing compounds. Cause for this lesion in the tongue is due to -

Black hairy tongue is a condition of the tongue in which the small bumps on the tongue elongate with black or brown discoloration, giving a black and hairy appearance. The appearance may be alarming, but it is a harmless condition. Predisposing factors include smoking, xerostomia (dry mouth), soft diet, poor oral hygiene and ceain medications. Management is by improving oral hygiene, especially scraping or brushing the tongue Hairy tongue largely occurs in the central pa of the dorsal tongue, just anterior (in front) of the circumvallate papillae, although sometimes the entire dorsal surface may be involved.Discoloration usually accompanies hairy tongue, and may be yellow, brown or black. Apa from the appearance, the condition is typically asymptomatic, but sometimes people may experience a gagging sensation or a bad taste.There may also be associated oral malodor (intra-oral halitosis). The term "melanoglossia' is also used to refer to there being black discolorations on the tongue without "hairs", which are also harmless and unrelated to black hairy tongue Ref Davidson 23rd edition pg 714