Intralesional melanocytic proliferation: This is a common occurrence in compound nevi, where there is an increase in the number of melanocytes within the nevus, leading to the appearance of brown spots.

Solar lentigines: These are benign lesions that can appear as brown spots, often in sun-exposed areas, and can be found in conjunction with pre-existing nevi.
Hori's nevus: A type of nevus that can present with brown spots or pigmentation, often seen in individuals with a history of sun exposure.
Nevus spilus: A congenital or acquired melanocytic lesion that can appear as a brown spot or patch, sometimes superimposed on a pre-existing nevus.

Melanoma: Although less likely, it is crucial to consider the possibility of melanoma, especially if the brown spots are new, changing, or exhibit asymmetry, border irregularity, color variation, diameter increase, or evolving characteristics.
Atypical melanocytic proliferation: This can be a precursor to melanoma and requires careful evaluation and possibly biopsy to rule out malignancy.

Nevus of Ota: A rare congenital melanocytic nevus that can present with brown or blue-gray pigmentation, often in the distribution of the ophthalmic and maxillary divisions of the trigeminal nerve.
Mongolian spot: A congenital melanocytic lesion that can appear as a brown or blue-gray spot, typically on the lower back, and may be mistaken for a nevus with brown spots.