I don't know how common it is, but it started fairly early on with us. The rectal sphincter was affected and led to frequent small discharges, of which my PALS was unaware as they were occurring. That's the reason we went to adult diapers early on. She never experienced urinary incontinence.
One potential side effect of Ativan is diarrhea. Though Annie had no desire nor need of it, the hospice folks badgered her into taking some (mechanically following their protocol). After taking it for 4 days Annie had her one and only episode of diarrhea. Much more serious is the potential side effect of permanent muscle weakness. Coincident with her taking Ativan and the diarrhea episode was a precipitous, rapid loss of her remaining muscle strength. Up until her taking the Ativan she was spending several hours a day typing on this forum. Suddenly she could no longer use her hands - that's when I started typing for her. The diarrhea episode incited me to research the possible side effects of Ativan, and these two potential side effects were among many that I found. Perhaps they were both simple coincidences, but I'm inclined to think not.
-Phil