LM is slowly growing, asymptomatic and often occurs in the setting of mottled hyperpigmentation. By the time they are biopsied, they are often larger in size (Fig. 3.2). In a retrospective study by Tiodorovic-Zivkovic et al., 48.8 % of lesions were > 10 mm in diameter at the time of biopsy. Similarly, 49.3 % of LMs biopsied had surrounding freckles, reinforcing the concept that these lesions arise in chronically sun-damaged skin (Fig. 3.3) [3].

Most LMs present as asymmetric brown-black macules or patches with variegated color and irregular borders [4]. The differential diagnosis includes solar lentigo, seborrheic keratosis (Fig. 3.4), lichenoid keratosis, pigmented actinic keratosis, and melanocytic nevus. In a study of 121 melanoma in situ lesions, 92 % were macular. In that same study, 75 % of the melanoma in situ lesions had asymmetric borders [4]. In a study of 186 melanomas of various subtypes (LM, superficial spreading melanoma, desmoplastic melanoma, and nevoid melanoma), light-and dark-brown were the most frequently seen colors [n = 161 (86.6 %) and n = 158 (84.9 %), respectively]. Pink was appreciated in 56 cases (30 %) while white was seen in 10 cases (5.4 %). Melanoma in situ most commonly demonstrated 2 colors [n = 97 (68.3 %)] while 9.9 % showed only 1 color and 21.8 % showed 3+ colors [5]. Infrequently it is even possible for LM/LMM to have an amelanotic presentation as depicted in Fig. 3.5.

In the early 1980s, a group of dermatologists created an algorithm for detecting melanomas based on their experience at NYU. At that time, melanoma detection was emphasized by Asymmetry, Border irregularity, and Color variegation [6]. This mnemonic has since been expanded to include Diameter greater than 6 mm and Evolution (lesions changing over time). The mnemonic ABCDEs of melanoma is commonly used by many physicians to raise melanoma awareness and educate the public about those lesions that may call for further evaluation. While this mnemonic can be used in evaluating lesions of LM/LMM, simply failing to notice which lesion to evaluate contributes to the delay in diagnosis. Most lesions of LM/LMM occur on the face and are plainly in view. Many have been followed for years by physicians and patients. The often larger size and longer duration before diagnosis speaks to their slow, stealthy growth, asymptomatic nature and camouflaged appearance against a background of photo damage (Fig. 3.6). These characteristics contribute to delay in diagnosis and highlight the need for the practitioner to maintain a high level of vigilance and suspicion, to sometimes step back and evaluate the patient’s skin globally and to notice pattern rather than individual lesion as stressed by the ABCDE mnemonic.

As above, LMs are slowly growing and often asymptomatic. They typically occur in patients who may have decreased vision and therefore identification of suspicious lesions often relies on the physician’s experience and level of suspicion. Clinicians seeing elderly fair skinned patients must remain vigilant and must carry a high index of suspicion and a low threshold for biopsy. A dermatoscope and/or a Wood’s lamp may aid the clinician in the decision to biopsy but given the degree of clinical overlap, definitive diagnosis often relies on histopathologic examination.