Diagnóstico por fluorescencia en el carcinoma basocelular previo a la cirugía micrográfica de Mohs

Abstract

The objective of this work is to evaluate the utility of fluorescence diagnosis before Mohs micrographic surgery, comparing the fluorescence area and the final boundary after surgery. Twenty-two patients who presented basal cell carcinoma were selected. The tumours for MMS treatment were selected according the histology and localization of the BCC. Fluorescence diagnosis was made the day before surgery. The fluorescence diagnosis corresponded exactly to the histological tumoural margins in only 3 patients (13.6 %). In the other 19 patients (86.4%) the fluorescence area was not the same as the histological tumoural margins. In 10 of these 19 patients (52.6%) the fluorescence area was smaller than the clinical and histological borders (False negative result). In 8 patients (42.1%) the fluorescence area was larger than clinically expected and larger than the final tumour boundary (False positive result). The sensitivity and specificity found was 25% and 0% respectively. The false negative results can be due to the use of this technique in some situations as a deep tumour or a low cellular density tumour. The main cause for false positive results may be due to the use of the technique in inadequate locations. Seborreic areas of the body produce basal fluorescence. In the central part of the face (particularly on the nose and lower eyelids) it is hard to differentiate the basal fluorescence from the tumoural fluorescence. In addition, generally, healthy skin surrounding the tumour can show perilesional fluorescence, which varies depending on the patient and the location of the tumor. Consequently it is difficult to systematize fluorescence results. Skin with severe actinic damage also shows fluorescence. Fluorescence diagnosis in a tumour located in these areas can provoke an unnecessary increase in the size of the resection area. Moreover, benign conditions such as recent scars or skin inflammation show non-specific fluorescence. All these limitations explain why fluorescence diagnosis is not useful before MMS. The indications for MMS are relapses, aggressive types, and tumours located on the central part of the face (H zone), just the type of tumors in which fluorescence diagnosis shows limitations. Due to all these limitations, fluorescence diagnosis does not seem useful for presurgical demarcation of tumour margins in this type of BCC.