A patient presents with a dark green-yellow discoloration on the dorsum of the tongue with elongated projections. What is the underlying histopathological finding?

Correct answer: B. Hyperkeratosis of the filiform papillae

• A. Atrophy of the fungiform papillae produces a smooth, red tongue (geographic tongue, atrophic glossitis) — not hairy/elongated projections.
• B. CORRECT. Hairy tongue (lingua villosa) is caused by hyperkeratosis (elongation) of the filiform papillae of the dorsal tongue. Normally, filiform papillae are shed regularly, but in hairy tongue, they fail to desquamate and elongate (up to 2 cm), trapping pigment-producing bacteria, food, and debris, resulting in the characteristic brown/black/green discoloration.
• C. The foliate papillae are on the lateral tongue (taste receptors) and do not produce elongated projections on the dorsum.
• D. The circumvallate (vallate) papillae form a V-shaped row at the junction of the anterior 2/3 and posterior 1/3 of the tongue — their hyperplasia does not produce the hairy tongue appearance.