- Malignant melanoma
- Benign freckle (ephelis)- very small, flat, uniformly brown spots with sharp borders that represent hyperpigmentation of the basal layer of the epidermis. The epidermal melanocytes do not increase in number, but extrude more pigment than normal into the basal epidermis.
- Most common in fair-skinned individuals
- May darken with sunlight exposure
- Typically located in malar region, but can be found anywhere on the face and neck (Figure 4)
- No treatment is necessary; can apply melanin-bleaching topical products
- Benign nevus (1–3 mm)- common lesions that arise from nevus cells, which are incompletely differentiated melanocytes found in clumps within the epidermis, dermis, and junction zone between these layers.
- Usually occur in childhood and increase at puberty
- Typically arise as flat, pigmented macules in childhood, representing junctional nevi
- Evolve into elevated/dome-like, pigmented compound nevi as they extend up into the epidermis and down into the dermis from the junctional zone
- In adulthood, the pigmented epidermal component involutes, resulting in a non-pigmented, amelanotic, dermal nevus (Figure 5)
- Frequently located on the eyelid margin, with typical appearance of molding to the globe along its posterior surface
- Malignant transformation of a junctional or compound nevus may occur, although rare
Figure 4. Differential diagnosis. Benign freckles, or ephelides, of the cheeks and nose demonstrating discrete, small, pigmented macules.
Figure 5. Differential diagnosis. Two dermal nevi are seen along the lateral crow's feet as elevated lesions, larger than ephelides. Pigmentation of the epidermal component fades with age, resulting in relatively amelanotic papules.
- Simple lentigines (lentigo simplex)- small flat, pigmented lesions slightly larger in diameter than freckles (but less than 3mm), that are not associated with sun exposure
- Increased number of uniformly dispersed single melanocytes without aytpia, as well as variable melanin located in the basal keratinocytes
- Eyelid simple lentigines may be associated with autosomal dominant polyposis of the gastrointestinal tract (Peutz-Jeghers syndrome)
- Solar lentigines (solar lentigo)- slightly larger, 3–5 mm, uniformly pigmented lesions in sun exposed areas due to increased numbers of melanocytes
- Often increase with age and sun exposure due to ultraviolet-induced mutations leading to enhanced melanin production and abnormal pigment retention by keratinocytes
- Uniformly hyperpigmented, and slightly larger than simple lentigines
- Most frequently located on forehead, jawline, décolletage, dorsal hands and arms (Figures 6 and 7)
- Histologically may also demonstrate a bulb-like elongation of rete ridges that form a reticular pattern due to interconnections between adjacent strands
Figure 6. Differential diagnosis. Multiple flat, pigmented macules on the forehead and pretrichial skin, consistent with solar lentigines.
Figure 7. Differential diagnosis. Multiple flat, uniformly pigmented macules on the thin skin of the dorsal hand, consistent with solar lentigines.
- Melasma: flat hyperpigmentation typically occurring on the forehead or periocular skin in women during or after pregnancy or with a history of oral contraceptive use, chronic dermatitis. or rosacea
- Seborrheic keratosis
- Lichen planus-like keratosis
- Pigmented actinic keratosis