Oral Pigmented Lesions: Differential Diagnosis

Oral pigmented lesions are a diverse group of conditions that appear as areas of abnormal color in the oral mucosa, ranging from brown and black...

Oral pigmented lesions are a diverse group of conditions that appear as areas of abnormal color in the oral mucosa, ranging from brown and black macules to blue and gray plaques. They arise from a variety of mechanisms, including the deposition of melanin, the accumulation of hemoglobin and its breakdown products, the presence of foreign material, and the growth of melanocytic or vascular tumors. Most pigmented lesions are benign, and many are normal physiological findings, but a small proportion represent malignant melanoma, a rare but aggressive cancer that can arise in the mouth. The clinician must therefore be able to recognize, classify, and appropriately investigate any pigmented lesion, because an early diagnosis of melanoma can be life-saving.

Classification of Pigmented Lesions

Pigmented lesions of the oral cavity are best classified according to their origin. Melanin-related lesions include physiological pigmentation, which is a normal variation seen most often in dark-skinned individuals, and a range of benign melanocytic lesions such as the oral melanotic macule, the melanocytic nevus, and the rare but important oral melanoma. Hemoglobin-related lesions include the hemangioma, the vascular malformation, and the varix, which appear blue or purple because of the blood within the vessels. The amalgam tattoo is a separate category, produced by the deposition of metallic particles in the mucosa, and a group of systemic conditions, including Addison disease and Peutz-Jeghers syndrome, can also produce oral pigmentation.

The distribution and the appearance of the lesion provide the first clues to its nature. Physiological pigmentation is usually diffuse and bilateral, following the attached gingiva, while the oral melanotic macule is a solitary, flat, brown or black spot that is most common on the lips and the buccal mucosa. The melanocytic nevus is a slightly elevated, well-defined lesion, and the amalgam tattoo appears as a blue-gray area with a characteristic metallic appearance on radiographs. Understanding these typical presentations allows the clinician to recognize the common benign lesions and to identify the features that demand biopsy.

Benign Melanotic Lesions

The oral melanotic macule is the most common cause of a solitary pigmented spot in the mouth. It is a benign, flat lesion that appears as a brown or black area, most frequently on the lower lip, the gingiva, and the buccal mucosa, and it represents a focal increase in the deposition of melanin within the basal layer of the epithelium without any proliferation of melanocytes. The macule is usually a few millimeters in size, well defined, and stable over time, and no treatment is required unless the patient wishes it removed for esthetic reasons.

The melanocytic nevus is less common in the oral cavity than on the skin but presents as a well-circumscribed, slightly elevated, brown or blue-black lesion that contains nests of nevus cells. The intraoral nevus is generally benign, and the management is usually observation or simple excision for confirmation. It is important to note that, although the majority of these lesions are harmless, the oral cavity is a site where malignant melanoma can develop, and any lesion that is growing, changing in color, or irregular in outline must be viewed with suspicion.

Vascular Lesions and Amalgam Tattoo

Vascular pigmented lesions appear blue, purple, or red because of the blood within the vessels, and they include the hemangioma, the vascular malformation, and the varix. The hemangioma is a proliferation of blood vessels that appears in infancy and grows, while the vascular malformation is a developmental anomaly that is present at birth and grows with the patient. The varix is a dilated vein that appears in older adults, most commonly on the lip or the ventral tongue, as a soft, blue, compressible nodule. These lesions are generally benign, and they may be left alone unless they bleed, interfere with function, or cause esthetic concern.

The amalgam tattoo is a common cause of an intraoral pigmented area and results from the implantation of amalgam particles into the mucosa during a dental procedure. It appears as a blue, gray, or black area, often near a restored tooth, and it is frequently mistaken for a melanotic lesion. The diagnosis is confirmed when a radiograph shows the characteristic radiopaque particles, and no treatment is required because the tattoo is inert and stable. The main importance of the tattoo is that it must be distinguished from a melanocytic lesion, and the radiograph is the key to this distinction.

Oral Melanoma and Red Flags

Oral melanoma is a rare malignancy that accounts for a small proportion of all melanomas but carries a poor prognosis, because it is often diagnosed late and tends to metastasize early. It most commonly arises on the hard palate and the maxillary gingiva, and it appears as a brown, black, or gray lesion that is irregular in outline, asymmetric, and frequently ulcerated or bleeding. The lesion grows progressively, and it may be accompanied by loosening of the teeth or a palpable mass. Any of these features, or a pigmented lesion that is changing or that has appeared suddenly in an adult, should arouse suspicion.

The clinical signs that indicate a need for urgent biopsy are summarized by the mnemonic that emphasizes asymmetry, border irregularity, color variation, diameter, and evolution. In the mouth, additional warning signs include a lesion that is larger than a few millimeters, one that is multifocal, one that arises in a site where pigmentation is unusual, and one that is associated with ulceration, bleeding, or pain. The definitive diagnosis is made by an incisional biopsy, which is mandatory for any suspicious pigmented lesion, and the histopathology determines the management, which typically involves wide surgical excision and oncological evaluation.

Diagnostic Workup and Biopsy

The assessment of a pigmented lesion begins with a thorough history and clinical examination, including the duration, the growth, and the presence of any symptoms, and an examination of the entire oral cavity and the skin. The clinician notes the distribution of any pigmentation, looking for the bilateral pattern of physiological pigmentation or the diffuse pigmentation of a systemic disease, and records the color, the size, the outline, and the surface of each lesion. A radiograph is taken where an amalgam tattoo or a vascular lesion is suspected, and the medical history may reveal a systemic cause of the pigmentation.

The decision to biopsy depends on the clinical assessment. A lesion that is stable, typical, and clearly benign may be observed, while any lesion with suspicious features, any lesion of unknown duration, and any lesion that is growing must be biopsied. The biopsy must be of adequate size and depth, and it is generally performed as an incisional biopsy that includes a portion of the normal mucosa at the margin. The histopathological examination then provides the definitive diagnosis, and the lesion is either reassured as benign or treated appropriately if it is malignant.

Clinical Key Points

Most oral pigmented lesions are benign and physiological.

The melanotic macule is the most common solitary pigmented spot.

The amalgam tattoo is confirmed by its radiopacity.

Oral melanoma is rare but aggressive and must not be missed.

Any changing, irregular, or ulcerated lesion requires biopsy.

Early diagnosis of oral melanoma can be life-saving.

Conclusion

Oral pigmented lesions confront the clinician with a wide spectrum of conditions that range from the completely benign to the potentially fatal, and the only safe approach is a systematic one. By classifying the lesion according to its origin, recognizing the typical appearances of the common benign conditions, and maintaining a high index of suspicion for the features of malignant melanoma, the clinician can reassure the great majority of patients and identify the rare but dangerous lesion at a stage when treatment can be effective. A pigmented lesion that is changing or suspicious must never be dismissed, because the early biopsy of an oral melanoma is the single most important factor in its prognosis.