A congenital cardiac abnormality . . . and other stories

BMJ 2017; 359 doi: https://doi.org/10.1136/bmj.j4981 (Published 02 November 2017) Cite this as: BMJ 2017;359:j4981

Polycystic ovary syndrome

Insulin resistance and obesity are features of polycystic ovary syndrome and cross sectional surveys show strong associations with type 2 diabetes. A longitudinal population based study from Denmark (J Clin Endocrinol Metabolism doi:10.1210/jc.2017-01354) confirms the link and quantifies the risk. Among more than 18 000 women with polycystic ovary syndrome the incidence of type 2 diabetes was four times higher than in age matched controls, and the median age at diagnosis was 4 years younger.

Bicuspid aortic valves

Bicuspid aortic valves are the commonest congenital cardiac abnormality, present in 1% to 2% of people. Most bicuspid valves arise from a fusion of two leaflets of a tri-leaflet valve. In a large series of adult cases, fusion of the right and left coronary cusps was most common, followed by fusion of the right and non-coronary cusps (Heart doi:10.1136/heartjnl-2017-311560). Fusion of the left and non-coronary cusps was rare. Aortic stenosis was most likely to occur in patients with the first type of fusion.

Cystatin C

Creatinine based estimates of glomerular filtration rate lead to overdiagnosis of chronic kidney disease and guidelines recommend that the diagnosis should be confirmed using cystatin C as a different measure of kidney function. In a large group of older people in a primary care setting, however, this approach resulted in more misdiagnosis rather than less (Plos Med doi:10.1371/journal.pmed.1002400). Although a small proportion were re-classified as not having kidney disease after cystatin C testing, nearly 60% were moved to a more advanced category of disease.

Exploring the insula

The insula is buried behind the cortex of the frontal, temporal, and parietal lobes and its functions are mysterious. More than 50 years ago the neurosurgeon Wilder Penfield reported that direct stimulation of the insula in conscious patients sometimes gave rise to olfactory and gustatory sensations. A more extensive study (Ann Neurol doi:10.1002/ana.25010) using stereotactically placed depth electrodes for presurgical evaluation in patients with epilepsy replicates the earlier observations. It locates the mid dorsal insula as an area of the brain involved in the conscious perception of flavours.

Exposure to air pollution in early life

Urban areas with the worst domestic air pollution in the early 1950s had the highest mortality rate from rheumatic heart disease half a century later according to a geographical analysis in England and Wales (Int J Epidemiol doi:10.1093/ije/dyw249). The investigators speculate that air pollution increased children’s susceptibility to infection with group A, β haemolytic streptococci. The finding might be of more than historic interest because rheumatic fever and rheumatic heart disease are still common in parts of the world where biomass fuels are widely used and levels of smoke pollution high.

Ecological fallacies

Studies based on aggregated data are vulnerable to the ecological fallacy. Associations observed at group level don’t necessarily hold for the individuals within those groups. It’s a potential problem with the study of air pollution mentioned in the story above. It also turned out to be a very real problem in an evaluation of hospital performance in the Netherlands (BMJ Qual Safety doi:10.1136/bmjqs-2017-006776) where hospital level associations between mortality, readmission, and length of stay often failed to reflect patient level associations. In patients with stroke, for example, longer length of hospital stay was related to reduced mortality, whereas hospitals where length of stay was long had higher mortality rates.

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