Definition
An oral/labial melanotic macule is a benign, focal pigmented lesion caused by increased melanin within the epithelium (and sometimes lamina propria) without an increase in the number of melanocytes. It is the most common oral mucosal lesion of melanocytic origin (also called focal melanosis). When on the lips it is termed a labial melanotic macule; intraorally, an oral melanotic macule.
Etiology and Pathophysiology
Contributory factors :
- Etiology has not been definitively determined; the macule may represent a reactive or a physiologic process.
- Caused by increased production and deposition of melanin within the basal cell layer, the lamina propria, or both — there is no increase in the number of melanocytes.
- Sun exposure does not appear to be a precipitating factor, and (unlike freckles) labial melanotic macules do not darken after sun exposure.
- May represent several different conditions (lecture): an intraoral freckle (localised increased pigment), post-inflammatory pigmentation (darkening following inflammation), or pigmentation as a manifestation of systemic disease.
- Systemic / syndromic associations: multiple melanotic macules may be seen in idiopathic disease, Addison disease, and Peutz-Jeghers syndrome (autosomal dominant, with intestinal hamartomatous polyps), as well as Laugier-Hunziker syndrome (with melanonychia), neurofibromatosis, McCune-Albright syndrome, Carney complex, and LEOPARD syndrome.
Prevalence
- Present in up to 3% of the population.
- Typically observed in the fourth and fifth decades, with a 2:1 female predilection.
- The most common oral mucosal lesion of melanocytic origin (focal melanosis); reported as ~62% of melanocytic lesions in one comparison.
- Labial melanotic macules are the most common type, frequently occurring on the lower vermilion (~33% of cases per one source).
Histological Features
- Increase in melanin in the basal and parabasal layers of normal stratified squamous epithelium.
- Normal numbers of melanocytes (no melanocytic hyperplasia) — histopathology is essentially the same as physiologic pigmentation.
- Melanin may also be seen within melanophages or lie free (melanin incontinence) in the subepithelial connective tissue.
- Mild acanthosis with little spongiosis; vascular ectasia; inflammation typically 0 to 1+.
- Lesions do not typically demonstrate elongated rete ridges.
Clinical Features
Location
- Labial melanotic macule — lower lip vermilion border is predominantly affected and is the most common overall.
- Oral melanotic macule — may appear on any mucosal surface; most commonly the buccal mucosa, gingiva, and palate. (Lecture: most common sites are gingiva and the vermilion border of the lips.)
- Intraoral lesions are often larger than those on the lips.
Appearance
- Solitary, well-circumscribed, evenly pigmented lesion, typically <1 cm in diameter.
- Uniformly tan to dark brown (described as tan-to-brown-to-black), round or oval, flat, and asymptomatic.
Differential Diagnoses
- Amalgam tattoo
- Melanocytic nevus / nevi
- Malignant melanoma (notably early melanoma, which can look similar)
- Freckle/ephelis, melanoacanthoma, and post-inflammatory (smoker’s) melanosis
- (Multiple macules: consider Peutz-Jeghers and other lentigines syndromes, Addison disease)
Relevant Clinical Investigations
- Biopsy is advised to confirm the diagnosis and rule out other pigmented lesions. An excisional biopsy is strongly advisable for any suspected oral/labial melanotic macule.
- Rationale: early malignant melanoma may have a similar clinical appearance and shows a predilection for the maxillary alveolar mucosa and palate; a melanotic macule cannot be reliably distinguished from melanoma clinically.
- If multiple/diffuse pigmentation or systemic features are present, investigate for underlying systemic/genetic disorders (e.g., Addison disease, Peutz-Jeghers syndrome).
Patient Management
- Considered a benign lesion without malignant potential.
- No specific treatment is required once a benign diagnosis is confirmed.
- Labial macules of cosmetic concern may be removed by scalpel, cryosurgery, electrocautery, or laser ablation.
- As a benign condition, patients should be reassured and not referred as urgent cases.