Discussion
B. Melanotic macules (MM) are benign, pigmented lesions that
clinically present as brown, flat discolorations of the oral mucosa,
representing 86.1% of melanocytic lesions of the lips and oral
cavity (Figure 4). 4, 5 The discoloration is caused by a focal increase
in melanin deposition with or without a concomitant increase in
the number of melanocytes. The cause is unknown, but it does
not appear to be dependent on sun exposure. This differs from
the common cutaneous freckle, or ephelis, which darkens in color
with sun exposure. However, it is hypothesized that MMs present
on the vermilion border may be related to actinic irradiation
(Figure 5). 2 Clinically, the lesion presents over a wide age range,
with an average age of 43 years, and a 2:1 female predilection. 4
MMs appear as asymptomatic, solitary, well-demarcated, tan to
dark-brown, flat lesions in 83% of cases. 2 The color is uniform
throughout the lesion. Patients occasionally present with multiple
macular lesions. Additionally, blue or black lesions have also been
reported. The most common locations are on the lower lip at the
vermilion border, followed by the buccal mucosa, gingiva
(commonly the maxillary anterior gingiva), and palate. 2, 4 MMs
reach their maximum dimension rapidly and remain constant
thereafter. Histologically, the lesion displays an increase in melanin
pigmentation in the basal and parabasal layers of normal, stratified
squamous epithelium, without elongated rete ridges. Melanin
incontinence (free melanin) may be seen in the subjacent
connective tissue. While MM was considered in the differential
diagnosis in this case, the presence of foreign material, the
staining of the reticulin fibers, and the absence of basal and
parabasal melanin ruled out this entity.
Figure 5
A flat, round, uniformly
pigmented melanotic
macule of the lower left lip.
MM is a benign entity with no potential for malignant transformation.
However, they are important for two reasons: 1) they may be an
oral manifestation of a systemic condition and 2) early oral
mucosal melanoma can appear similar clinically. In addition to
an idiopathic cause, cases of multiple, pigmented, flat lesions
may be associated with systemic conditions (e.g., Peutz-Jeghers
syndrome, McCune-Albright syndrome, Addison disease) or
certain medications or irritants can increase melanin pigmentation
(e