The differential diagnosis for agminated blue nevi includes segmental melanocytic nevi, melanoma, and other agminated melanocytic nevi: benign melanocytic nevi, atypical or dysplastic nevi, and speckled lentiginous nevi (nevus spilus).
The distribution of the nevi can help narrow the differential, as segmental melanocytic nevi are less clustered and spread over a larger area than agminated blue nevi.
The presence or absence of background pigmentation can help distinguish between agminated blue nevi and nevus spilus.
Agminated blue nevi and nevus spilus can be differentiated in the clinic by using a Wood's lamp or performing a biopsy, which is not indicated unless atypia is present.
Differential diagnoses included a pigmented epithelioid melanocytoma, an agminated
Spitz nevus, or a "low-grade" melanoma (Clark's level III, Breslow thickness 3.