Not strictly IBS but a few patients with collagenous colitis (cc) are misdiagnosed with IBS. Collagenous colitis causes watery diarrhoea which can be confused with IBS-D. I suffered from CC a few years ago and managed to find a way to achieve full remission. I have added a topic to my IBS/Hypothyroidism describing this relatively safe and simple treatment. See http://ibshypo.com/index.php/collagenous-colitis/