All known types of amyloid affect the gastrointestinal tract, including amyloid A (AA), amyloid of lambda (AL), or kappa light chain origin, transthyretin amyloid (ATTR), and β2-microglobulin (β2M). They may be distinguished using a panel of immunohistochemical markers (572). A recent study showed that the most common forms of large intestinal amyloid were AL amyloid followed by AA and ATTR. There were also cases in which the classification of the amyloid type was uncertain (572). Gastrointestinal amyloidosis generally presents as a motility disorder, ulcers, areas of hemorrhage, or pseudotumors.

The colorectum also develops α₂-microglobulin deposits, the latter affecting patients on long-term dialysis (573). The development of the amyloidosis correlates with the time on dialysis (574). Patients with α₂-microglobulin deposits exhibit two patterns of amyloid deposition: A vascular pattern and a gastrointestinal pattern. The vascular pattern may be subtle and not be evident in H&E-stained sections but can be highlighted by stains for amyloid or a microglobulin immunostain (574). The amyloid deposits may associate with mild mucosal abnormalities and regeneration or there may be ischemic damage. The severity of the mucosal changes reflects the severity of the vasculopathy. In the gastrointestinal pattern the amyloid deposits in the interstitium of the mucosa, submucosa, and muscularis propria. This pattern coexists with the vascular pattern. The amyloid deposits range from barely visible amyloid without mural expansion to amyloid tumors in the muscularis propria (573,574,575).