| Seborrheic keratosis is a very common benign lesions of the skin in elderly people, and it is thought as a developmental disorder caused by the local maturational arrest of keratinnocytes.It can occur in any age, but the incidence significently increased with age. There is still some debate about whether there is some difference of the incidence between male and female, recent research implied that the difference is extremely trifling. The etiology of seborrheic keratosis is not clear, it is suggested that exposure to sunlight, infection with human papilloma virus and inheritance have significant correlation with seborrheic keratosis. In recent years, many investigation indicated that the apoptosis play an important role in the development of seborrheic keratosis, the factors which take part in the control of the cell cycle include CyclinE, P21WAFI/CIP1, P16, PCNA, EGF, EGFr, etc. The expression of those factors in seborrheic keratosis is abnormal, which leads to the disorder of cell differentiation, proliferation, apoptosis and cell cycle, and eventually participate in the accurrence of seborrheic keratosis. The lesions can occur everywhere of the body, but more often on the exposed area,such as the face, the head, the neck, the outer forearms, etc, but less on the palms and the base of stapes. In different stage of the development, the lesions can show different apperance. In the initial stage, they are pink or light brown and smoothpatches, then grow larger to round or oval plaques, which have a papilloma-like suface. The plaques are dark brown or black, and have thick crust on them. And sometimes the leision has an atypical clinical appearance, so seborrheic keratosis are most often confused clinically with other pigmental disease, such as pigmented nevus, verruca planae, actinic keratosis, pigmental basal cell carcinoma, maligenant melanoma, etc. Then the histological diagnosis is indispensable. In order to enhance the accuracy of diagnosis, we studied retrospectively of 191 cases of seborrheic keratosis that accepted pathological examination in our hospital from 1987 to 2006.Methods: We used statistic analysis in order to investigate the incidence of male and female, average age, site difference, clinical misdiagnosis, etc.Results: In 191 cases, there were 96 males (50.26%), and 95 females (49.74%). The average age of the seborrheic keratosis patients was 52.1±15.6 years, and 53.6±16.2 years for males, 50.5±15.0 years for females. The course of disease was 4.1±9.1 years per person. In terms of the site of leisions, 76 cases (39.8%) occurred on the exposed area and 104 cases (54.5%) on the partly exposed area. When the estimated body surface area (BSA) (adapted from New York University's Dermatologic Formulary) was taken into account, the leisions on exposed area were over-represented compared with the partly exposed area. There was a patient with Leser- Trélat (LT) signin the 191 cases. The patients emerged the increase lesions of itchy multiple seborrheic keratosis in an eruptive manner, in a short period of time, and then was diagnosed carcinoma of rectum. According to the standard adapted by Zhao Bian's Clinical Dermatology, seborrheic keratosis is divided into six histological subtypes: acanthonic, hyperkeratotic, adonoidal or reticulated, clonal, irritated, melanoacanthoma variants. In 191 cases, the number of acanthonic cases was 69 (36.1%), hyperkeratotic cases was 58 (30.4%), adenoidal cases was 9 (4.7%), clonal cases was 7 (3.7%), irritated cases was 18 (9.4%), melanoacanthoma case was 1 (0.5%), and there was an interim type in all cases, the cases'number of this type was 29 (5.2%). In our research, 64 cases were misdiagnosed to the other disease, including 36 cases (56.3%) misdiagnosed to pigmented nevus, and others to verruca planae, epidermo-dysplasia verruciformis, cutaneous tag, Bowen's disease, malignant melanoma, etc.Conclusions:1. Seborrheic keratosis can occur in any age, but the incidence significantly increased with age. The incidence between male and female doesn't have significant difference.2. Exposure to sunlight is a possible risk factor of seborrheic keratosis.3. Histopathological examination is a reliable method to diagnosis of seborrheic keratosis, the leisions resembling SK shouldsubmit for histopathological examination immediately.
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