Perimenstrual asthma: a syndrome without known cause or cure.

Perimenstrual worsening of asthma has been documented in 30% to 40% of asthmatic women. This increase in symptoms has been backed up by increased health care use perimenstrually, as well as by cyclic variation in peak expiratory flows. The cause of perimenstrual asthma (PMA) remains unclear. Fluctuations in hormone levels, their ratios, or both are a plausible explanation but have not been demonstrated with any consistency. Influences of sex hormones on inflammation is an area of future research, as are hormone-induced changes in smooth muscle function and beta-adrenergic receptors, prostaglandin levels, and fluid retention in the bronchial mucosa. In the light of the high prevalence of PMA, it is difficult to understand why there has been no randomized controlled trial of hormone therapy. Nevertheless, several case reports have suggested beneficial effects of estrogens, progestins, and their combination. In light of these positive case reports, well-designed, double-blind studies of sufficient sample size should now be performed to give treatment of PMA an evidence base.