A 74-year-old woman has noted increasing size and number of darker brown patches on the dorsum of each hand for the past 15 years. They do not change with sun exposure, are nonpruritic, and non-tender. On examination, these 0.5- to 1-cm lightly pigmented lesions are flat. Which of the following is the most likely microscopic finding in these lesions?

Unlike a freckle that darkens upon light exposure, lentigo (pleural:lentigenes) does not. There is a focal increase in melanocytes of the basal layer, along with thinning of epidermis and elongation of rete ridges. Lentigines can occur at any age; those in older persons may be termed senile lentigines or age spots. A nevus typically forms a nodule and likely appears much earlier in life. Loss of melanin is termed vitiligo and is a separate process from melanocyte hyperplasia. A collection of mast cells can produce urticaria pigmentosa, which often has a light brown appearance, but pruritus is common. Some superficial fungal infections (black piedra) may be pigmented, but they typically do not persist for years.