Black Spots on the Labia
Black spots on the labia are most commonly called "vulvar melanosis" (also termed labial melanotic macules or genital lentiginosis), which are benign pigmented lesions characterized by increased melanin in the basal layer of the epidermis without melanocytic atypia. 1, 2
Clinical Characteristics
Vulvar melanosis presents as single or multiple asymptomatic macules or patches that are dark brown to black in color, ranging from 1-5 mm in size, with asymmetric borders that may be poorly defined. 2, 3
- The most frequent location is the labia minora (43% of cases), followed by the labia majora (26%) 2
- These lesions are intensely pigmented irregular macules that can clinically mimic malignant melanoma, creating significant anxiety for both patients and physicians 1, 2
- The condition is benign, with no documented malignant transformation during long-term follow-up studies (median 13 years) 2
Dermoscopic Features
Dermoscopy reveals characteristic "landscape painting patterns" in approximately 81% of labial melanotic macules, consisting of parallel or circular lines with overlapping vessels against a brown pigmented background. 3
- Background brown pigmentation is present in 92.5% of lesions 3
- Parallel lines appear in 77.5% of cases 3
- A "structureless" pattern with blue hue (indicating melanophages in the upper dermis) is common in clinically equivocal vulvar melanosis 4
Important Differential Diagnoses to Exclude
Peutz-Jeghers syndrome must be considered when melanotic macules are present on the lips and genitalia, particularly if accompanied by buccal mucosa pigmentation (which never occurs with simple freckles) or a family history of gastrointestinal polyposis. 5
- Peutz-Jeghers pigmentation consists of dark brown or blue-brown macules 1-5 mm in size on the vermilion border of lips (94%), buccal mucosa (66%), and genital areas 5
- This syndrome carries increased cancer risk and requires gastrointestinal surveillance 5
Pigmented areas within lichen sclerosus require biopsy to exclude abnormal melanocytic proliferation or squamous cell carcinoma, as 60% of vulvar SCCs occur on a background of lichen sclerosus. 5
When to Biopsy
Biopsy is mandatory when lesions are pigmented AND exhibit any of the following features: induration, fixation, ulceration, failure to respond to therapy, or occur in immunocompromised patients. 6
- Histopathology of benign vulvar melanosis shows marked lower epidermal pigmentation without melanocytic atypia or nesting 1
- Approximately 2% of pigmented vulvar lesions are nevocellular nevi, which are histologically identical to nevi elsewhere on the body 7
Management
Reassurance is the only treatment required for confirmed vulvar melanosis, as it is a completely benign condition. 1
- Lesions may increase in size and change color over time (30% of cases) but ultimately stabilize without malignant transformation 2
- An association with hormonal status exists, as 67% of patients with vulvar melanosis are premenopausal and 65% have received hormone therapy 2
- Annual clinical and dermoscopic photography is reasonable for monitoring, though not strictly necessary given the benign natural history 2
Critical Pitfall
Do not delay biopsy when black spots have atypical features (asymmetry, irregular borders, color variation, diameter >6mm, evolution), as melanoma of the vulva has a poorer prognosis than melanoma elsewhere due to delayed diagnosis. 7