High density of small nerve fibres in the functional layer of the endometrium in women with endometriosis

BACKGROUND: Endometriosis is a common gynaecological disease and is frequently associated with recurrent and serious pelvic pain such as dysmenorrhoea and dyspareunia, but the mechanisms by which these symptoms are generated are not well understood. METHODS: Histological sections of endometrial tissue were prepared from endometrial curettings and hysterectomies performed on women with endometriosis (n = 25 and n = 10, respectively) and without endometriosis (n = 47 and n = 35, respectively). These were stained immunohistochemically for the highly specific polyclonal rabbit anti-protein gene product 9.5 (PGP9.5) and monoclonal mouse anti-neurofilament protein (NF) to demonstrate both myelinated and unmyelinated nerve fibres. RESULTS: Small nerve fibres were identified throughout the basal and functional layers of the endometrium in all endometriosis patients, but were not seen in the functional layer of the endometrium in any of the women without endometriosis (P < 0.001). NF-immunoreactive nerve fibres were present in the basal layer in all endometriosis patients but not in non-endometriosis patients, with one exception (P < 0.001). CONCLUSIONS: Small nerve fibres detected in the functional layer in all women with endometriosis may have important implications for understanding the generation of pain in these patients. The presence of nerve fibres in an endometrial biopsy may be a novel surrogate marker of clinical endometriosis.