Over-use of steroids is another systemic trigger. Many of these can be avoided. Many of these seem to be related to digestion. Retained placenta after foaling another trigger. I have also heard of several incidents where vaccinations, particularly rabies, triggered laminitis.
Some medical conditions can make a horse more likely to founder, such as low thyroid.
Another sign is a long, curly coat slow to shed out. The tumor grows slowly and the signs develop gradually. The tests are ACTH and Dex suppression. There is medication available to control it, but it is expensive. Malnutrition is a subtle thing.