Gender differences in incidence of idiopathic fistula-in-ano are not explained by circulating sex hormones.

The observed increased incidence of idiopathic anal fistulae in men compared with women cannot be explained by the cryptoglandular hypothesis alone. Male predilection is even more pronounced in neonates and is also seen in the canine population. Investigations into hormonal aspects of hidradenitis suppurativa suggest a possible influence of androgens in its pathogenesis. In order to investigate the possibility of a similar effect in fistula-in-ano, we have compared a range of circulating sex hormones in 15 male and 12 female patients with anal fistulae with those in equal numbers of age-matched controls. There were no differences in levels of any measured hormones between male patients and healthy controls. There was no evidence of increased androgenisation of female patients. Women with fistulae had higher levels of circulating oestradiol (253 vs 163 pmol/l, medians, P = 0.03) and lower levels of progesterone (1.05 vs 3.0 nmol/l, medians, P = 0.039) than healthy women. Further work is merited to investigate the possibility of increased local androgen conversion in anal glands.