What is an irritated compound naevus?

What is an Irritated Compound Naevus?

An irritated compound naevus is a benign melanocytic lesion that has undergone trauma or inflammation, causing reactive changes that can mimic concerning features but remains fundamentally benign.

Definition and Pathophysiology

A compound naevus consists of nevomelanocytes located in both the epidermis (junctional component) and dermis (dermal component). 1 When subjected to trauma, friction, or inflammation, these lesions develop reactive changes termed "irritation," which can create diagnostic confusion with melanoma. 2

• The irritation typically results from mechanical trauma, repeated friction (especially in intertriginous areas), or inflammatory processes 2
• These reactive changes include increased melanocytic proliferation, architectural distortion, and inflammatory infiltrate 2
• The lesions commonly appear as pigmented papules that may show recent changes in size, color, or texture due to the irritation 1

Clinical Presentation

Irritated compound naevi frequently occur in young patients and are predominantly found on the trunk and intertriginous areas where trauma is more likely. 2

• Patients may report recent changes such as darkening, enlargement, or development of symptoms like itching or tenderness 3
• The lesions can appear asymmetric or show irregular borders due to the inflammatory response 2
• Polypoid or raised appearance is common, particularly after repeated trauma 2

Histopathological Features That Distinguish Irritation from Malignancy

The key to diagnosis is recognizing that despite atypical junctional features, the dermal component shows reassuring maturation with depth and negligible cytologic atypia. 2

Features commonly seen in irritated compound naevi:

• Asymmetry (30% of cases) and shouldering (47.5%) 2
• Poor circumscription (37.5%) 2
• Deep extension of melanocytes along adnexal structures (67.5%) 2
• Variable junctional atypia related to trauma and regeneration 2

Reassuring features that confirm benignity:

• Dermal component demonstrates maturation with depth and minimal cytologic atypia 2
• Absence of deep dermal mitoses or only rare superficial dermal mitoses (10% or less) 2
• Molecular studies show no melanoma profile 2
• Homogeneous p16 expression pattern (unlike melanoma which shows complete or heterogeneous loss) 4

Diagnostic Approach

Full-thickness excisional biopsy with 2 mm margins is essential for accurate diagnosis, as partial biopsies may lead to misdiagnosis. 4, 5

• Dermoscopy by an experienced physician should be performed prior to biopsy to enhance diagnostic accuracy 4
• The biopsy should be elliptical with the long axis parallel to skin lines to allow for re-excision if needed 4, 5
• Shave biopsies must be avoided as they lead to incorrect diagnosis due to sampling error 3, 5

Management Recommendations

No further intervention is needed if pathology confirms a benign compound melanocytic nevus with clear margins, even if irritation features are present. 3

When observation is appropriate:

• Clear margins on initial excisional biopsy 3
• Histopathology confirms benign features with dermal maturation 2
• Annual dermatology evaluation is sufficient for isolated compound nevi without concerning features 3

When reexcision IS indicated:

• Conservative reexcision with 2-5 mm margins is appropriate only when margins are positive 3
• If the lesion represents the patient's only atypical nevus and margins are positive 3

Critical Pitfalls to Avoid

The most common error is overdiagnosis of irritated compound naevi as melanoma due to reactive junctional atypia. 2

• Avoid routine reexcision of all compound nevi with clear margins, as this represents overtreatment with no demonstrated benefit 3
• Do not perform ablative procedures (lasers, curettage, dermabrasion) as they obscure future melanoma evaluation and cause pigment recurrence 3
• Do not rely solely on junctional atypia for diagnosis—always assess the dermal component for maturation 2
• Recognize that polypoid compound melanocytic nevi can exhibit variable junctional atypia related to trauma and regeneration, which should not be mistaken for malignancy 2

Patient Surveillance

Patients should monitor for specific warning signs that differ from expected irritation changes. 3

Monitor for:

• Rapid or asymmetric growth beyond the initial irritation 3
• Color variation or heterogeneous darkening (not uniform darkening from irritation) 3
• Development of nodules 3
• Bleeding, ulceration, or persistent erosions 3
• Pain or significant pruritus that persists beyond the acute irritation phase 3