Pigmented Lesions of the Oral Cavity
In later stages, nevus cells are present in the connective tissue only, making these intradermal( skin) or intramucosal( oral) nevi. Melanin pigmentation may be seen in the superficial nevus cells and usually diminishes deeper in the connective tissue. While IMN was considered in the differential diagnosis of oral pigmented lesions in the current case, the absence of the aforementioned theques of nevus cells and melanin pigment ruled out this diagnosis.
Current evidence does not suggest that oral nevi are at an increased risk of developing melanoma— an outcome seen more commonly in their cutaneous counterpart. However, a biopsy is necessary for definitive diagnosis due to the variety of clinical appearances of IMN and potential overlap with oral mucosal melanoma.
D. Oral mucosal melanoma( OMM) is rare in the U. S., and accounts for less than 1 % of all melanomas. 2 Furthermore, primary OMM accounts for only 0.26 % of all oral cavity malignancies. Some reports have suggested a higher frequency in certain countries— specifically Japan and Uganda. 7 However, these racial groups commonly have a lower incidence of cutaneous melanoma in general, so the data may not be representative. Unlike most cases of the more common cutaneous melanoma, OMM is not related to sun exposure, and it has been suggested that OMM could result from exposure to irritants or carcinogenic compounds in the air. 7
OMM is often a nodular lesion at the time of diagnosis, but early OMM can present as a flat lesion with melanosis. 8 The lesions commonly present in the 5th through 7th decades and have a male predilection. 7 The majority present on the hard palate and maxillary alveolus. 7, 8 One out of three patients diagnosed with OMM had a history of a pigmented macule in the tumor region before diagnosis. 7 While occasionally not pigmented, they usually present as a black or brown macule with irregular borders. Non-pigmented lesions often have a normal mucosal color or a vascular appearance. It presents first as a macule that extends laterally and eventually becomes a lobulated, exophytic mass once it enters a stage of vertical growth. Ulceration may or may not be present early in lesional development, and often is not present at the time of diagnosis.
Radiographically, irregular,“ moth-eaten” destruction characteristic of malignancies may be seen if the underlying bone is involved. Cervical lymph node metastasis is often present at the initial presentation. Histologically, there is a proliferation of pleomorphic and hyperchromatic malignant melanocytes, which demonstrate different cellular growth patterns( e. g., spindle-shaped or epithelioid). 2 Of note, pigment is absent in around 10 % of cases, leading to overlap with other high-grade malignancies. 2
While OMM should be considered in the clinical differential diagnosis of oral pigmented lesions, the current case demonstrated no proliferation of atypical melanocytes, and the diagnosis of OMM was ruled out.
OMMs are aggressive malignancies, often presenting at a minimum of stage III, Treatment usually involves radical surgery combined with adjuvant radiation and / or chemotherapy. 7 OMM has a poor prognosis due to the difficulty in achieving a wide surgical margin free of tumor and the early hematogenous spread, especially if bone invasion exists. 8 Ultimately, death usually results from distant metastasis.
In conclusion, any pigmented lesion of the oral cavity should be thoroughly evaluated by clinicians. Biopsy of oral pigmented lesions is indicated for definitive diagnosis, especially those of recent onset, with irregular borders, and with large size. Radiographs of recent onset pigmented lesions in the area of previously removed or freshly placed amalgam restorations can be beneficial in making the clinical diagnosis of AT, eliminating the need for a biopsy. Although OMM is much rarer than the other oral pigmented entities in the differential diagnosis discussed for this case, given the poor prognosis and propensity to spread quickly, prompt evaluation and potential biopsy of pigmented lesions is highly recommended.
Acknowledgements
The authors would like to thank Dr. Edward L. Witek for his clinical image contribution.
References
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34 JULY / AUGUST 2017 | PENNSYLVANIA DENTAL JOURNAL