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REACTIVE CHANGES IN MELANOCYTIC TUMOURS: DIAGNOSTIC IMPLICATIONS

Wolter J. MooiDepartment of PathologyVU University Medical CentreAmsterdam, NLwj.mooi@vumc.nl

Disclosures: none

REACTIVE CHANGES IN MELANOCYTIC TUMOURS: DIAGNOSTIC IMPLICATIONS

• Recent physical trauma• Past (healed) physical trauma• Sun-induced changes• Concomitant non-neoplastic skin diseases• Concomitant skin neoplasms

Naevus with focal epidermal defect, presumably caused by trauma

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Naevus with focal epidermal defect, presumably caused by trauma Recurrent naevus after shave excision

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Histological features of recurrent naevus• Shave excision scar, covered by more or less flat neo-

epidermis• Remnants of naevus in adjacent pre-existent dermis: entirely

banal histological features• Within the scar, recurrent naevus is atypical:

• Irregular nests and solitary cells along the dermoepidermal junction• Sometimes a few ascending melanocytes• Compact nests and small nodules of naevus cells in the scar tissue• Naevus cells are enlarged, variably hyperpigmented; mild degree of

anisonucleosis• The atypical features are entirely restricted to the scar tissue

and overlying neo-epidermis

Posttraumaytic changes can also occur in melanoma!Female, 81 year. Irregular pigmented lesion of ankle. History of trauma.

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Three years later: excision of recurrent lesion

Biopsy trauma

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Naevus with fibrosis due to pressure or friction

• Area affected is generally the raised central part of a compound naevus

• The fibrosis and associated mild architectural atypia of the naevus cell population is restricted to this area

• These lesions are most common in body sites where recurrentpressure or friction are most likely, such as:• back• elbow, knee• sole of foot

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Naevus with folliculitis• A classical extrinsic cause of change in a previously stable

naevus• Erythema• Pain or itch• Swelling

• NB: intrinsic causes of change in a previously stable naevus include:• Malignant transformation• Combined naevus (with DPN-component)• ? MBAIT / BAPoma

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Associated spongiotic dermatitis (Meyerson naevus) or unrelated spongiotic dermatitis

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Various other non-related skin diseases

• Morphea• Lichen sclerosus• Bullous dermatoses• &c

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Associated lichenoid inflammatoryresponse• May occur in melanocytic naevi as well as in

melanoma in situ or invasive melanoma

• The underlying melanocytic lesion may not immediately be apparent• Clinically• Histologically

Female, 40 yrs. Punch biopsy, skin of back. Superficial BCC?

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Lichenoid dermatitis obscuring or simulating a melanoma (or melanoma in situ)?

Melan-A

PNL-2

Chronic solar damage

Paucicellular lentigo maligna versus reactivemelanocyte hyperplasia in sun-damaged skin

The assessment of resectionmargins in LM may yield less than equivocal results, because of overlap of features of LM and reactive melanocyte proliferation and atypia

LENTIGO MALIGNA REACTIVE MELANOCYTIC HYPERPLASIA

Lentiginous spread with or without nests Lentiginous spread only; no nests

Melanocytes often directly side-to-side (rather thanseparated by basal keratinocytes)

Melanocytes usually not directly side-to-side

Spread well into hair follicles Spread into hair follicles is not marked

Ascent common Ascent uncommon

Marked cytological atypia in at least some of the cells common

Marked cytological atypia is uncommon

Clinically: single hyperpigmented lesion Clinically: no obvious single pigmented lesion

Melanocytic neoplasms colliding with other skin proliferations• Not very rare. Usually not a diagnostic problem• Pitfalls:

• Naevus or melanoma with dermal spindle cell tumours• Spitz naevus with pseudo-epitheliomatous hyperplasia

• The reverse may also consitute a pitfall: melanocytic colinization of epithelial skin tumours and breast cancer

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Sometimes, two diagnoses are better than one…• Neoplastic and nonneoplastic skin diseases

are exceedingly common, so that the a priori chance of two diseases/lesions in one biopsy is not that small…

• The interpretation of melanocytic neoplasms may be significantly influenced by non-melanocytic skin disorders, clinically as well as histologically

• Ockam’s razor may work against us, in this respect.

By Fred the Oyster [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons