Limitations
There are three main limitations to this review. Firstly to include sufficient studies we could not restrict the time period and the selected studies ranged over forty years. However the methodology for identifying DELC and CAD remained unchanged in that period and we believe all included studies are relevant. Secondly, although studies used fairly consistent definitions of DELC and CAD, there was some variance especially in the length of the crease. Three studies also used >70% stenosis of at least one major epicardial vessel to define CAD when the majority used 50% but it is not possible to determine the impact that had on their results. Studies also varied in using unilateral or bilateral creases to define DELC, although it was noted that including unilateral creases appeared to reduce the odds ratio and therefore significant results were still considered valid. Lastly some studies used non-cardiac patients as controls and it was assumed that they had no coronary artery disease without undergoing angiography. We recommend that, for consistency, further studies assess bilateral DELC and use Shresta’s(24) definition of a deep (>1mm) diagonal crease extending obliquely at least two-thirds from the tragus towards the outer border of the ear. This should be assessed by two examiners with the patient upright and patients with ear piercings which could cause iatrogenic creases should be excluded. Similarly CAD should be defined as >50% stenosis of at least one major epicardial vessel on angiography for both case and control groups.