Significance of the smooth muscle cell component in Peutz-Jeghers and juvenile polyps.

We have previously reported the presence of smooth muscle cells (SMCs) in the lamina propria of both tubular and villous adenomatous polyps. In the current study, we investigated the presence and distribution of SMCs with immunohistochemical techniques using anti-alpha smooth muscle actin and anti-desmin antibodies on a series of hamartomatous polyps. In five Peutz-Jeghers polyps, large tree-like branches of SMCs were observed, while in 13 juvenile polyps, rare elongated SMCs were found in the lamina propria, partially surrounding cystically dilated glands. Apart from the quantitative differences, the SMC distribution was similar in the two types of hamartomatous polyps and not dissimilar from the pattern described in neoplastic polyps. These findings make the category "juvenile polyp" less clear and its differentiation from other histologic types of polyp less sharp. Thus, the presence or absence of SMCs cannot form the basis of the differential diagnosis between adenomatous and hamartomatous polyps.