Confocal microscopy, dermoscopy, and histopathology features of atypical intraepidermal melanocytic proliferations associated with evolution to melanoma in situ

Abstract

Background Atypical intraepidermal melanocytic proliferations (AIMP) is a descriptive term sometimes applied to biopsies that do not fulfill diagnostic criteria of melanoma. They are common on sun-damaged skin, but their definition and management are controversial.Objective To describe dermoscopic (DS), reflectance confocal microscopic (RCM) and histopathological features of AIMP and identify features associated with subsequent melanoma in situ (MIS). Methods A retrospective analysis of AIMP lesions correlated with patient outcome at two melanoma tertiary centers between 2005 and 2015. Results Thirty-four patients were included. Nine (26%) patients had MIS in subsequent biopsies. Predictors of later MIS were target-like pattern (OR:12.0 [CI: 1.23, 117.41]; P = 0.032) and high-density vascular network (OR:12 [CI: 1.23-117.41], P: 0.032) on DS, and presence of dendritic cells touching each other (OR:9.1 [CI: 1.54, 54.59], P = 0.014) on RCM. Clinical predictors of worse outcome included a previous history of MIS at the same site. Radiotherapy for AIMP had a high failure rate (all patients presented with recurrent disease, three as AIMP and two as MIS).Conclusions Considering that most cases in this series received non-surgical treatment at baseline, we recommend close monitoring for lesions with target-like pattern and density vascular network on DS and treatment for lesions with progression of atypia and/or with "confluent" dendritic cells on RCM. Although the number of patients in this series is very low, early surgery is recommended for MIS cases that recur as AIMP.

Computer-aided diagnosis of reflectance confocal images to differentiate between lentigo maligna (LM) and atypical intraepidermal melanocytic proliferation (AIMP)

“…The main features used to differentiate between LM and AIMP both histologically and on RCM are the confluence and location of atypical melanocytes (Rocha et al, 2022). In LM, these are present at all levels of the epidermis; however, in AIMP, whilst the melanocytes are enlarged, there is no pagetoid spread, and they are present only in basal layers.…”

“…Distinguishing between AIMP and LM is important as AIMP may only require ongoing monitoring while LM usually requires some form of definitive treatment before it may progress to invasion and possibility of metastasis (lentigo maligna melanoma). AIMP, in contrast to LM, can continue to be monitored in vivo and tends not to respond to topical or radiotherapy treatments (Rocha et al, 2022). Thus, correct diagnosis determines the level of treatment required.…”

“…Reflectance confocal microscopy (RCM) is an in vivo imaging modality that enables large cutaneous lesions in cosmetically sensitive areas to be visualised to the depth of the papillary dermis without the requirement of a biopsy for formal histological assessment. The changes seen in Lentigo maligna (LM) and atypical intraepidermal melanocytic proliferation (AIMP, elsewhere known as atypical melanocytic hyperplasia, or AMH) involve the levels above the papillary dermis and are thus ideal candidates for the use of RCM for diagnosis (Koller et al, 2009; Rocha et al, 2022).…”

“…Further complicating the issue, AIMP has been shown to be, in fact, LM on further excision in 5% of cases (Bou-Prieto et al, 2021). Predictors of AIMP progression to LM have not been well defined, though could include a target-like pattern and high-density vascular network on dermoscopy, and the presence of contact between dendritic cells on RCM (Rocha et al, 2022). This may indicate that a binary classification approach to diagnosis is a simplification of an underlying spectrum of pathologies between AIMP and LM.…”

Differentiation Between Benign and Malignant Pigmented Skin Tumours Using Bedside Diagnostic Imaging Technologies: A Pilot Study

“…It is possible that most lesions currently reported as naevi with atypical intraepidermal melanocytic proliferation (AIMP) are, in fact, benign, and that their significance lies in the potential pitfall for overdiagnosis of malignant melanoma. However, this pilot study included AN in the malignant category, since studies have shown that up to 20% of these lesions are diagnosed as melanoma in situ (MIS) in pathology revisions ( 28 ). Furthermore, it has been demonstrated previously in a retrospective study that the risk of evolution to MIS in AIMP lesions is higher in lesions that demonstrate a high number of dendritic cells touching each other in RCM images ( 28 ).…”