MKSAP Quiz: Dark spot on lower lip

MKSAP Answer and Critique

The correct answer is D. Melanotic macule. This content is available to MKSAP 18 subscribers as Question 33 in the Dermatology section. More information about MKSAP is available online.

Melanotic macule or mucosal lentigo is a small, well-circumscribed, brown-to-black macule. The most common location is the lower mucosal lip, but they can occur on any mucosal surface. They are the mucosal counterpart of a lentigo on the skin. They are typically solitary, but multiple macules can occur. Numerous mucosal lentigines are associated with various syndromes such as Peutz-Jeghers and Laugier-Hunziker syndromes. Peutz-Jeghers syndrome is an autosomal dominant hamartomatous polyposis syndrome characterized by hamartomatous polyps in the gastrointestinal tract, mucocutaneous pigmentation, and an increased risk of cancer. Laugier-Hunziker syndrome is an acquired, benign disorder characterized by lentigines on the lips and buccal mucosa. It is not associated with any systemic disorder.

Actinic cheilitis appears as chronic red-to-tan scaly patches with erosions and characteristically involves the lower lip. Actinic cheilitis is a premalignant condition and is considered the precursor to squamous cell carcinoma in situ. Treatment with topical chemotherapy agents (5-fluorouracil), imiquimod, laser therapy, photodynamic therapy, or cryotherapy is recommended. Actinic cheilitis differs from angular cheilitis, which is inflammation involving one or both corners of the mouth and often related to a bacterial or fungal infection.

Amalgam tattoos are the most common source of localized pigmentation on the buccal mucosa. Amalgam dental fillings contain metals that can become implanted into the adjacent mucosa at the time of application. They appear as blue-gray macules and do not change over time. The typical location for amalgam tattoos is the buccal mucosa, not the lip. Diagnosis can be made clinically, or confirmation can be made with biopsy and pathology. No treatment is necessary.

Although it can arise anywhere in the skin or mucous membranes, malignant melanoma most commonly occurs in sun-exposed areas. The back is the most common location in men, and the legs are the most common location in women. The clinical features that suggest melanoma are asymmetry, irregular border, multiple colors, diameter greater than 6 mm, and changing size. The more of these features a pigmented lesion possesses, the more worrisome it is for malignant melanoma or melanoma in-situ, and these entities must be excluded with an excisional biopsy. This patient's lesion is small, round, well-circumscribed and has no worrisome features of a melanoma.

Key Point

• Melanotic macules are well-circumscribed, brown-to-black macules that most commonly occur on the lower lip, although they may be seen on the gingiva, buccal mucosa, or tongue.