The non-invasive skin imaging in dermatology clinic to provide clues for the diagnosis and differential diagnosis of skin diseases is worldwidely accepted in the past two decades, among which, the RCM could image the epidermis and the upper dermis in cellular resolution. And the cellular changes of the lesion in different layers could be imaged and compared with that of the adjacent normal skin. The RCM had been used during the past two decades,in the detection, or differential diagnosis of benign and malignant skin tumors., and,the RCM features of these tumors was investigated with high sensitivity and specificity [9,10] compared with the histology results, .In latest research, the study with RCM were increasingly detailed and deep, in which, the determination of skin tumor boundary before surgery, the detection and follow-up of cutaneous tumor metastasis were explored[11,12]. Imaging the skin conditions with RCM to avoid or reduce the invasive biopsy on exposed areas is of increasingly interest. RCM may be considered a promising tool for differential diagnosis of syringoma and milia[13] ,and a non-invasive arsenal for the assessment of hair and scalp disorders, benefiting patients[14]. Even compared with the novel imaging device,such as the optical coherence tomography, and multiphoton microscopy , the RCM embodies its unique advantages[15-16].
The papular lesion of SK is easily misdiagnosed as verruca plana (VP). Previously, we performed a study[17] to differentiate SK and verruca plana based on the RCM imaging ,and we found that SK shows a cerebriform shape while VP has petal-like structures, which correlates well with the papillomatous hyperplasia of SK and vacuolized keratinocytes of VP in histology images.
The patch or plaque lesion of SK can be difficult to distinguish with LK by naked eye. The previous study using dermoscopy to image the LK lesions showed features of SK like fingerprinting along with focal granularity[18,19], indicating dermoscopy may be less conspicuous in the differential diagnosis of LK and SK.
The main RCM features of LK were investigated and correlated with histology results in several recent studies[20-23]. The typical RCM feature of LK[20,21] was found in DEJ with elongated cords, bulbous projections, milia-like cysts, and some bright round cells were also seen within the inter-papillary spaces.
Based on their findings, we investigated 10 cases, clinically suspicious of SK, with single light brown or dark brown patch or plaque lesions on face. For SK lesions, the typical characteristics are the cerebriform pattern of the epidermis, or the pattern of the elongated cords with bulbous projections, without significant infiltrate of inflammation in dermal -epidermal junction, based on the RCM imaging. While for LK lesions, the typical features are the DEJ disarray and inflammatory infiltration in the superficial dermis. The most important image feature to differentiate LK and SK is the presence of DEJ disarray and inflammatory infiltration in the superficial dermis, or not, in RCM images
After care analysis of the RCM images, 4 of the 10 cases were determined as LK, 6 as SK, and the RCM results were well correlated with histology analysis, highlighting the role of RCM in differential diagnosis of LK and SK.
The differential diagnosis of LK and SK is important, for the treatments are different. The lesions of SK could subside completely after several sessions of laser treatments without significant side effects, while the treatment of LK with lasers is more difficult, which needs more sessions and lead to great probability of post inflammation hyper-pigmentation, for the lichenoid inflammation reaction of LK. The common treatment of LK is calcineurin inhibitor or imiquimod cream[23].not lasers.
In this study, we focused on LK, which is easy to be confused with SK by naked eyes. Clinically, there may be some SK, that should be differentiated with actinic keratosis or basal cell carcinoma[24], which indicates the important role of RCM in screening and differential diagnosis of LK.
In summary, we investigated the role of RCM in the differential diagnosis of LK and SK, and we found the presence of DEJ disarray and inflammatory infiltration in the superficial dermis is the main point of LK,which is different from SK,The RCM plays an important role in the differential diagnosis of LK and SK.
The main limitation of our study is the limited samples, for the biopsy of the facial tissue is different to be obtained. We need more cases to confirm our findings in further study.