In June 2003, a 40-year-old female patient from and resident of a town near Guatemala City presented for consultation referred by her general dentist with an asymptomatic dark brown pigmented macule, discovered during a routine clinical examination. The lesion was located on the anterior mucosa of the hard palate, measuring 0.5 cm in diameter. The patient had no relevant medical history and was in good health. She reported not taking any medication. The patient had lost her upper incisors through exodontia and was wearing a removable partial denture made of acrylic, inadequately designed, which caused pressure erythema of the underlying mucosa, candidiasis was ruled out by exfoliative cytology.

An excisional biopsy was performed under local anaesthesia using the punch technique with a 0.6 cm diameter instrument. The surgical site healed by second intention without complications.
The tissue obtained from the biopsy was fixed in 10% buffered formalin and processed routinely. Microscopic examination with haematoxylin-eosin stain revealed a mucosal fragment lined by mildly acanthotic stratified squamous epithelium with spongiosis, containing numerous dendritic melanocytes. The underlying connective tissue showed the presence of melanin pigment admixed with a mild lymphocyte-predominant inflammatory infiltrate. The definitive diagnosis was melanoacanthosis.