Dermoscopic presentation of a 2-mm melanoma in situ

Abstract

A 37-year-old woman first presented in 2003 with an irregularly bordered, slightly elevated, brown-black plaque on her left lower leg and a history of the mole changing over a period of 6 months. Upon excision, the diagnosis of melanoma in the setting of pre-existing naevus, Clark level III, Breslow thickness 0.9 mm, was made. Standard staging work-up disclosed no significant abnormalities. The patient was subsequently managed via 3-monthly clinical surveillance and at the second follow-up visit in April 2004, a new 2-mm light-brown, bluish macule was detected on the left thigh (Fig. 1a). Dermoscopic examination revealed asymmetry of colour and structure, uneven distribution of brownish and bluish irregular streaks and some bluishblack dots with elements of an atypical pigment network (Fig. 1b). The excisional biopsy of this lesion revealed the histopathological features of a melanoma in situ, namely nests of melanocytes with varied size and shape, confluent junctional nest of melanocytes (Fig. 2a) as well as increased numbers of atypical melanocytes at the dermo-epidermal junction and in the upper layers of the epidermis (Fig. 2b). Despite the ABCD rule, a significant proportion of melanomas do not fit the D criterion of 6 mm. In fact small melanomas have a reported frequency of 11.4–38.2% of all diagnosed melanomas. In view of a complete skin examination with dermoscopy requiring less than 3 min, we propose all lesions be routinely evaluated under dermoscopy, regardless of the size. In conclusion, this case illustrates the timely diagnosis of a small second primary melanoma, due to adherence to routine follow up with judicious clinical and dermoscopic examination. © 2010 The Authors Journal compilation © 2010 The Australasian College of Dermatologists