Pathophysiology of merkel cell

Abstract

The objective of this review is to introduce Merkel cells (MCs), to provide a basic overview on the theoretical background of function, development and clinical importance of MCs. The origin of human MCs have been controversial. Some investigators believe that it is a neural crest derivate, whereas others have proposed that it is a differentiation product of the fetal epidermal keratinocytes. MCs are cells primarily localized in the epidermal basal layer of vertebrates and concentrated in touch-sensitive areas in glabrous, hairy skin and in some mucosa. In routine light microscopy, human MCs can hardly be identified. Cytokeratin 20 (CK20) is a reliable marker with highest degree of specificity. MCs can be also distinguished by electron microscopy. MC carcinoma (MCC) is an uncommon and often aggressive malignancy and found mainly in elderly patients. It occurs most frequently in the head and neck region. Diagnosis is based on typical histological presentation on hematoxylin and eosin (H and E) stained slides together with the results of immunohistochemistry. Histologically, MCC has been classified into three distinct subtypes: Trabecular, intermediate and small cell type.

Keywords: Cytokeratin 20; merkel cell carcinoma; merkel cells.

Figure 1

Merkel's cell located in the region of the stratum basale, associated with nerve axon (lower arrow). (Courtesy: James K Avery; Nancy Avery; Pauline F Steele, editors. Oral Development and Histology. New York: Stuttgart: Thieme Medical Publishers, 2002)

Figure 2

Electron micrograph of Merkel cell in the basal layer of oral epithelium. The cytoplasm of this cell is filled with small, dense vesicles situated close to an adjacent unmyelinated nerve axon. Arrowheads point to the site of the basal lamina. (Courtesy: Antonio Nanci Tencate's Oral histology- Development, Structure and function, 7 th ed. St. Louis: Missouri Mosby an imprint of Elsevier; 2008)

Figure 3

The histologic variants of Merkel cell carcinoma are shown: (a)Trabecular type (H&E stain, ×100), (b) Intermediate type (H&E stain, ×400) and Small cell type (H&E stain, ×400). (Courtesy: Goessling W, McKee PH, Mayer RJ. Merkel cell carcinoma. J Clin Oncol 2002;20:588)