“Research highlights” is a weekly round-up of research papers appearing in the print BMJ. We start off with this week’s research questions, before providing more detail on some individual research papers and accompanying articles.

• What risk of mortality is associated with tiotropium delivered by mist inhaler in patients with chronic obstructive pulmonary disease?
• Is cryotherapy with liquid nitrogen more clinically effective than 50% salicylic acid for treatment of plantar warts?
• Are maternal snoring and supine sleep position associated with increased risk of late stillbirth?
• What are the outcomes of pregnancy in women admitted to hospital with H1N1 influenza in pregnancy?
• Could deficiencies in the cancer registration system explain the lower survival after cancer in the UK?

Mortality associated with use of tiotropium mist inhaler
The tiotropium mist inhaler is aimed at patients with chronic obstructive pulmonary disease who find it hard to take this anticholinergic drug via a standard inhaler. It is available in more than 50 countries but not yet in the United States, perhaps because there has been conflicting evidence on the cardiovascular safety of inhaled anticholinergics and because this inhaler leads to relatively high plasma concentrations of the drug. Sonal Singh and colleagues’ meta-analysis of five randomised controlled trials with a total of 6522 patients found that, when compared with placebo, the mist inhaler was associated with a significantly increased risk of mortality. The authors estimated that the number needed to treat for a year with the 5 µg dose to see one additional death was 124 (95% confidence interval 52 to 5682). The authors urge clinicians to tell patients about the possibility of this increased risk and to be cautious when prescribing tiotropium mist inhaler, particularly in patients with possible underlying cardiac disease (doi:10.1136/bmj.d3215).

Freezing warts is no more effective than keratolysis with salicylic acid
For such a common problem, we know surprisingly little about the best treatment for cutaneous warts.  Now Sarah Cockayne and colleagues have compared, in a randomised controlled trial, two of the most common treatments (and the only ones with a good evidence base), cryotherapy with liquid nitrogen and salicylic acid (at 50% strength), on plantar warts.  They found no difference in effectiveness at 12 weeks but suggest that, since cryotherapy is more costly, salicylic acid is the more attractive treatment.

However, with cure rates of only 14% for both treatments, one might also conclude that they are probably no more effective than a wait and see policy—as Jan Nico Bouwes Bavinck and colleagues do in their accompanying editorial. They also point out that little is known about the epidemiology of the various types of human papillomavirus that cause warts and their sensitivity to different treatments, so it may be unsurprising that treatments often fail. Despite most warts clearing spontaneously quite quickly, many cause problems from discomfort or disfigurement for a definitive treatment to be desirable.

Late stillbirth and maternal sleeping position
The Auckland Stillbirth Study was set up to identify potentially modifiable risk factors for late stillbirth (≥28 weeks’ gestation), for which there is usually no medical explanation. Maternal obesity is one of the known risk factors, but the underlying mechanisms for its association with stillbirth are not understood. Since obesity is also associated with sleep disordered breathing, this could be a possible explanation.

In this week’s BMJ Tomasina Stacey and colleagues report on the association between maternal sleep practices and late stillbirth risk, using self reported snoring and daytime sleepiness as markers for sleep disordered breathing. They found no relation between either marker and risk of late stillbirth, but women who slept on their back or on their right side on the last night of pregnancy (the night before when the woman thought that her baby had died or, for the controls, the night before interview) were twice as likely to have a late stillbirth as women who slept on their left side. The absolute risk of late stillbirth remained low, however: for those who went to sleep on their left it was 1.96 stillbirths per 1000 and for those who slept in any other position it was 3.93 per 1000. The study also found a high correlation between a woman’s position on going to sleep and her position on waking up, so it looks as though pregnant women tend to stay in the same sleeping position overnight.

The authors warn that this novel finding needs to be replicated in other studies before public health recommendations can be made. In a linked editorial, Lucy Chappell from King’s College London, says “any simple intervention that reduces the risk of stillbirth would be extremely welcome,” but warns that these findings need to be interpreted with extreme caution. She concludes that “a forceful campaign urging pregnant women to sleep on their left side is not yet warranted” and that this study is only hypothesis generating.