A focal blue-grey pigmented macule is noted on the mucosa. All of the following belong in the differential diagnosis EXCEPT:

Correct answer: B. Fibroma

• A. Blue nevus is a benign proliferation of dendritic melanocytes deep in the connective tissue. The depth is what makes it look blue — the Tyndall effect scatters shorter wavelengths — and the palate is its most common oral site.
• B. CORRECT as the EXCEPTION. A fibroma is a reactive fibrous hyperplasia — a firm, dome-shaped nodule that is the same colour as the surrounding mucosa or slightly paler from surface keratinisation. It is not a pigmented lesion at all, so it has no place in the differential for a blue-grey macule.
• C. Amalgam tattoo is the single most common cause of a focal blue-grey macule in the mouth, produced by metallic particles embedded in connective tissue during restorative or surgical work. Larger fragments may be radiopaque on a periapical film, which can settle the diagnosis without a biopsy.
• D. Oral melanoma is rare but must always be considered for a pigmented lesion. The palate and maxillary gingiva are the classic sites, and irregular borders, colour variegation or documented growth mandate biopsy.

Note: The pigmented-lesion differential to memorise: amalgam tattoo, melanotic macule, blue nevus, melanoma, physiological (racial) pigmentation, smoker's melanosis, and drug-induced pigmentation (minocycline, antimalarials). If a lesion is pigmented, growing and irregular, biopsy it — do not observe it.