Oral Melanoacanthoma 

Updated: Jun 26, 2018
Author: Talib Najjar, DMD, MDS, PhD; Chief Editor: Jeff Burgess, DDS, MSD 

Overview

Background

Melanoacanthoma is a rare condition of oral mucosa that has been reported only in the last century. The lesion is characterized by a proliferation of both melanocytes and keratinocytes that results in pigmented macular or plaquelike lesions (see image below).

Intraoral melanoacanthoma lesion on the mandibular Intraoral melanoacanthoma lesion on the mandibular gingiva.

Oral melanoacanthoma is regarded by many as a reactive condition unrelated to cutaneous melanoacanthoma, but the histologic features are similar. Cutaneous and mucosal melanoacanthoma differ in terms of patient age, patient race, and site.

In 1927, Bloch provided the earliest known description of melanoacanthoma, which was reported in the German literature.[1] Bloch described several skin lesions, which he originally called benign nonovoid melanoepithelioma of the skin. He further subdivided his cases into 2 types: In the histologic samples studied, type 1 had both dendritic melanocytes and keratinocytes, whereas the histologic appearance of type 2 was similar to that of type 1, but it lacked the dendritic melanocytes.

In 1960, Mishima and Pinkus reexamined the condition and further refined the diagnostic terminology.[2] The condition that Bloch designated as type 1 is currently called melanoacanthoma, and type 2 is currently called pigmented seborrheic keratosis.[3]

Although cutaneous lesions of melanoacanthoma were reported as early as 1927, Tomich et al at the American Academy of Oral Pathology first reported oral mucosal lesions in 1978.[1] Although many authors subsequently published case reports, Goode et al published the first case report in 1983.[4] This was a retrospective review of 10 cases of oral melanoacanthoma reported in the literature.

To date, oral melanoacanthoma remains a rare condition, with approximately fewer than 100 reported cases. The cutaneous variant is also rare; however, it is more prevalent than the mucosal variant.

Pathophysiology

The mucosal variants of melanoacanthoma have histologic appearances similar to that of cutaneous melanoacanthoma. The lesion consists of proliferating melanocytes and keratinocytes, which result in large pigment-containing dendritic cells. The dendritic cells are present throughout the middle and upper layers of the epithelium. See the image below.

Diagram of a pigmented epithelial macule. Diagram of a pigmented epithelial macule.

Inflammation occurs almost universally in patients with mucosal lesions. The presence of inflammation and the spontaneous resolution of oral lesions are suggestive of a reactive process rather than a neoplastic process.[5] The observation of trauma and inflammation associated with oral lesions has led to the conclusion that the mucosal variant is likely the result of a reactive process rather than a neoplastic process.[6]

Etiology

The role of trauma in the development of the lesion remains controversial, but any irritant must be removed. BRAF inhibitor therapy may play a role in some cases.[7]

Epidemiology

US frequency

Oral melanoacanthoma is rare, with only approximately fewer than 100 cases reported since 1978,[8, 9, 10] when the lesions were first reported. The cutaneous variant is more common, but it is still relatively rare among skin lesions. Among all the cases reported, specific patterns are described with respect to the race, sex, and age of patients with cutaneous melanoacanthomas and those with mucosal melanoacanthomas.

Race

Cutaneous lesions of melanoacanthoma are reported almost exclusively in white patients. The mucosal variant is reported almost exclusively in black patients.[11, 12] Some sporadic mucosal cases are reported in Asian individuals.

Sex

The prevalence for both variants of melanoacanthoma is fairly equal in both sexes, with a slight female predominance.[13] The female-to-male ratio is approximately 3:2.

Age

The age distributions of the 2 types of melanoacanthoma differ.[14] Cutaneous lesions are found in patients with a mean age of approximately 60 years. Mucosal lesions appear in patients with a mean age of approximately 25 years.

Prognosis

Initially, cutaneous lesions were suspected to be malignant, and subsequently, the lesions were linked to a transformation to low-grade malignancy. Malignant transformation has been reported in at least 2 cases. However, most lesions are considered benign and should be treated conservatively.

No cases of recurrence or metastasis have been reported in either the mucosal variant or cutaneous variant. A low risk of recurrence exists. To date no malignant oral melanoacanthoma have been reported.

 

Presentation

History

Because the lesions of oral melanoacanthoma are not painful, physicians usually discover them on routine oral examination.

Physical Examination

The clinical features of oral melanoacanthoma may mimic those of other pigmented lesions. For example, the clinical and histologic features of oral melanoacanthoma lesions can resemble those of melanoma in situ.

Cutaneous lesions are as follows:

  • Cutaneous lesions are reported in the scalp, eyelid, ear, nose, neck, thorax, and abdomen.

  • Cutaneous lesions may be found on any area of the head and neck, as well as on the chest, abdomen, back, or legs.

  • The lesions are generally asymptomatic, flat or slightly raised hyperpigmented areas.

  • The color of the lesions ranges from brown to black to blue.

  • Lesions are usually isolated, with no apparent precipitating factors.

  • Lesions are slow growing and are usually present for months before treatment is sought.

Mucosal lesions are as follows:

  • Mucosal lesions can occur in the buccal mucosa, labial mucosa, palate, gingiva (see image below),[15] alveolar ridge, or lip.[16, 17]

    Intraoral melanoacanthoma lesion on the mandibular Intraoral melanoacanthoma lesion on the mandibular gingiva.
  • Although the appearance of mucosal lesions is similar to that of cutaneous lesions, mucosal lesions have a more rapid onset and rate of growth.[18]

  • Mucosal lesions occur mostly on the lip,[19] buccal mucosa,[20] or palate,[21] and they are precipitated by a traumatic event.

  • The diameter of the mucosal lesions can range from a few millimeters to several centimeters.

 

DDx

Diagnostic Considerations

Also consider the following:

  • Melanoma in situ
  • Melanosis
  • Superficial melanoma
  • Junctional melanocytic nevus
  • Melanotic macule
  • Pigmented basal cell epithelioma
  • Nevoid eruptive keratoacanthoma [22]

Differential Diagnoses

 

Workup

Procedures

The clinical features of cutaneous and mucosal lesions may mimic those of other pigmented lesions; therefore, definitive diagnosis is based on histologic examination. Incisional or excisional biopsy may be performed based on the size and the anatomic location of the lesion. Insulinlike growth factor 2 mRNA-binding protein-3 has been suggested to help histologically differentiate keratoacanthoma from squamous cell carcinoma.[23]

Histologic Findings

Microscopic examination reveals a hyperplastic edematous stratified squamous epithelium with acanthosis and elongated widened rete ridges.[24] Increased melanin pigmentation is present in the basal layer (see image below). In addition, many proliferating dendritic melanocytes or clear cells extend upward into the prickle-cell layers (see image below).

Increased melanin pigmentation in the basal layer Increased melanin pigmentation in the basal layer of a melanoacanthoma (hematoxylin and eosin, original magnification X10).
Proliferating dendritic melanocytes in the prickle Proliferating dendritic melanocytes in the prickle-cell layers of a melanoacanthoma (hematoxylin and eosin, original magnification X40).

The clinical and histologic features of oral melanoacanthoma lesions can resemble those of melanoma in situ.[25] Usually, no evidence of cellular pleomorphism or abnormal mitotic activity is seen in oral melanoacanthomas, and this feature excludes malignancy.

In mucosal lesions, mixed chronic inflammatory cells and numerous melanin-laden macrophages densely infiltrate the stratum corneum. This inflammatory process may indicate the reactive rather than the neoplastic nature of the lesion.[26, 27]

 

Treatment

Medical Care

No medical treatment for mucosal or cutaneous lesions is known. A low risk of recurrence exists. In patients with mucosal lesions, treatment may be limited to the removal of the precipitating stimulus.[28] Lesions spontaneously resolve in approximately 40% of patients with oral lesions.[2]

Surgical Care

Surgical excision is the treatment of choice for both mucosal and cutaneous lesions. Because rare cases of premalignant or malignant cutaneous lesions are reported, wider resection with clear margins is recommended. In benign cutaneous melanoacanthoma, local excision or ablation of the site is adequate. If mucosal lesions do not resolve, local excision or ablation is indicated.

Cryosurgery, electrosurgery, or laser treatment[29] may be used to remove lesions; however, these modalities may jeopardize the microscopic diagnosis.

Complications

No evidence of malignant transformation has been reported. No complications arise from incisional or excisional biopsy.