Details
Back lesion. Previous shave biopsy showed severely dysplastic nevus.
"Recurrent nevus phenomenon" describes the relatively rapid recurrence of a melanocytic lesion after incomplete removal. Upon recurrence, although most are readily correctly diagnosed, some recurrent nevi with atypical features may be difficult to distinguish from melanoma and have overlapping features with regression. 20-28% of recurrent nevi have been shown to originate from dysplastic nevi, and in these cases, there may be more atypia than usual.
Challenging features include pagetoid scattering of melanocytes, rare mitotic figures, nuclear atypia, and lentiginous hyperplasia. Clinically benign nevi, removed for cosmetic reasons, may continue to be done so via less invasive means, but all lesions should be examined histologically, and compared to the original biopsy, if necessary. HMB-45, tyrosinase, and K1-67 may be helpful in difficult cases.
Clinically, it commonly presents in women 20-30 years of age, most frequently on the back, within 6 months of biopsy. It appears as a macular area of scar variegated with hyper- and hypopigmentation in linear, halo, stippled, or diffuse patterns.
Recurrent nevi show a tri-zonal growth pattern, characterized by: 1) a circumscribed melanocytic lesion within the epidermis, with no spread laterally beyond the original lesion; 2) atypical melanocytes confined to the epidermis; 3) increased numbers of melanocytes singly and in nests, within and above the basal layer; 4) variation in size and shape of nests, which can be confluent or discrete; 5) few atypical melanocytes; 6) few mitoses; 7) fibrosis in papillary and occasionally reticular dermis; and 8) sparse, superficial, and perivascular lymphohistiocytic infiltration.
This case reveals re-excision of skin with focal residual dysplastic nevus overlying a prominent central dermal scarring reaction consistent with prior procedure/biopsy. The epidermis overlying the scar shows hyperpigmentation and some irregular lentiginous melanocytic growth with focal nesting. The melanocytes show moderate density and mild cytologic atypia. It does not extend beyond the area of dermal scarring and does not involve the resection margins. This is consistent with limited residual dysplastic nevus with associated post-surgical hyperpigmentation and melanocytic regrowth.
This slide shows H&E stain. See related content for Melan-A stain.
See related content for references:
1) Fox, JC., et al. Arch Pathol Lab Med. 2011; 135(7):842-6
