When no underlying cause can be identified an effort is still usually made to eliminate as many of the common causes as possible,
by using a wide spectrum dewormer (usually fenbendazole) to try to rule out parasites, dietary food trials to try to identify food sensitivities and allergies, biopsy of the intestines to try to rule out cancers and to
aid in identifying other underlying causes and
by the use of
antibiotics to try to rule out the bacterial overgrowth / toxin issues.