Recurrent melanocytic naevus (pseudomelanoma)
Pseudomelanoma; persistent melanocytic naevus; recurrent naevus phenomenon; "Kornberg-Ackerman naevus"
A recurrent melanocytic naevus — historically termed pseudomelanoma — is a benign pattern of repigmentation in a scar from a previously incompletely excised or shave-biopsied melanocytic naevus. It typically appears within weeks to a few months as a streaky, asymmetric, irregularly pigmented brown patch confined within the scar borders. Because it is asymmetric, irregularly pigmented and shows histological atypia (pagetoid scatter, mitoses, suprabasal melanocytes), it is the single most clinically important post-procedural mimic of recurrent melanoma — a misdiagnosis that leads to wide local excision and sentinel-node assessment for what is in fact a benign re-growth. The cardinal management principle is to review the original biopsy specimen before any further intervention: if the original lesion was unequivocally a benign naevus and the recurrent pigmentation is clinically and histologically confined to the scar, observation or simple re-excision is appropriate.
When and why does this occur?
- Following incomplete excision of a benign compound or junctional naevus — most often after shave biopsy or punch biopsy that did not capture the full naevus.
- Residual benign melanocytes at the deep or peripheral margin proliferate and migrate into the healing scar.
- Reactive epidermal changes plus scattered residual melanocytes produce an alarming clinical and histological picture.
- Onset typically within 3–6 months of the original biopsy; sometimes years later.
- Children and young adults more often affected (more naevi, more biopsies).
Clinical features
- Asymmetric, irregularly pigmented brown to black streaks or patches within (and confined to) a previous biopsy or excision scar.
- The pigmented changes do not extend beyond the scar borders — a key clinical clue.
- Asymptomatic; occasionally mildly itchy.
- Background scar tissue may be erythematous and contracted.
- Differential — recurrent melanoma (extends beyond scar; nodular component), tattoo / foreign-body pigment, post-inflammatory hyperpigmentation, lentigo maligna in adjacent sun-damaged skin (especially on face).
Histology & pitfalls
- Histology mimics melanoma: junctional and intraepidermal melanocytes, pagetoid scatter, suprabasal mitoses, asymmetry — but features are confined to the epidermis above the scar.
- Beneath the dermal scar — only mature dermal melanocytes (the residual naevus), without atypia or mitoses.
- Critical pitfall: assessing the recurrent biopsy in isolation, without the original specimen, leads to a melanoma diagnosis. The original specimen must be retrieved and reviewed by the same dermatopathologist.
- Differential by histology: recurrent melanoma — atypical melanocytes deep beyond the scar (in the dermis and subcutis), mitoses in dermal cells, nodular component beneath scar.
Management
- Step 1 — review the original biopsy specimen:
- If unequivocally benign: the recurrent pigmentation is almost certainly a recurrent benign naevus. Observe with photographic surveillance, or perform conservative re-excision for diagnostic / cosmetic reasons.
- If atypical or borderline / dysplastic: re-excise to clear margins.
- If melanoma was missed at original specimen: definitive wide local excision per AJCC 8 thickness margins, ± sentinel lymph node biopsy.
- Step 2 — re-biopsy: full excisional biopsy of the recurrent lesion for histological assessment, with the dermatopathologist provided the original specimen and clinical history. Comparison side-by-side resolves most cases.
- Avoid shave biopsy of the recurrent lesion — incomplete sampling perpetuates the cycle.
- Counsel the patient about cosmetic implications and surveillance.
Prevention
- Complete excisional biopsy with adequate margins is the single most effective preventive strategy for any clinically suspicious melanocytic lesion.
- Avoid shave biopsy or partial sampling of clinically atypical pigmented lesions.
- Ensure histology confirms complete excision of any naevus excised for diagnostic concern.
References
- Kornberg R, Ackerman AB. Pseudomelanoma — recurrent melanocytic nevus following partial surgical removal. Arch Dermatol; 1975.
- King R et al. Recurrent melanocytic naevus — clinicopathological review. J Cutan Pathol; 2009.
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