| Blue rubber bleb nevus syndrome | GI bleeding from venous malformations in gut; chronic anemia > acute hemorrhage | Dark blue papules, nodules |
| Cowden disease | Esophageal acanthosis; stomach, small intestine, colon polyps; colorectal cancer | Facial trichilemmomas, oral papillomas with cobblestoning, acral keratoses |
| Cronkhite-Canada syndrome | Polyposis stomach and bowel; abdominal pain, severe protein-losing enteropathy | Patchy alopecia, nail changes, hyperpigmentation |
| Ehlers-Danlos syndrome, vascular | Diverticula, hernias, bowel perforation (sigmoid colon) | Thin translucent skin, characteristic facies, acrogeria |
| Hereditary hemorrhagic telangiectasia | GI bleeding, most commonly stomach or duodenum | Mat telangiectasias (arteriovenous malformations) |
| Gardner syndrome | Adenomatous polyposis | Epidermoid cysts, fibromas, lipomas, pilomatricomas, facial osteomas |
| Muir-Torre syndrome | Colorectal cancer | Sebaceous neoplasms, keratoacanthomas |
| Neurofibromatosis I | GI stromal tumors | Café-au-lait macules, axillary freckling, neurofibromas, Lisch nodules |
| Peutz-Jeghers | Hamartomatous polyposis, mainly small intestine, recurrent intussusception; increased risk adenocarcinoma | Pigmented macules around mouth, lips, buccal mucosa, digits |
| Carcinoid syndrome | Small bowel tumors cause 75%; abdominal cramps, diarrhea | Flushing, pellagra, facial edema and induration |
| Glucagonoma | Chronic diarrhea, abdominal pain, glucose intolerance, diabetes mellitus | Necrolytic migratory erythema |
| Kaposi sarcoma | GI bleeding | Red/purple macules, papules, plaques, or nodules on skin and mucosa |
| Typhoid fever | Abdominal pain, diarrhea, constipation, intestinal perforation | Rose spots—salmon-colored macules on trunk |
| Henoch-Schönlein purpura | Abdominal pain, vomiting, bloody diarrhea, intussusception | Palpable purpura of legs and buttocks |
| Malignant atrophic papulosis | GI bleeding, abdominal pain, diarrhea, bowel perforation | Crops of porcelain-white atrophic papules with telangiectatic border |
| Polyarteritis nodosa | Abdominal pain, nausea, melena, diarrhea; mesenteric arteritis, bowel ischemia | Subcutaneous nodules, livedo reticularis, ulcers |
| Crohn disease | Granulomatous inflammation of the bowel, often with skip lesions | Aphthae, granulomatous cheilitis, oral cobblestoning, erythema nodosum, vasculitis, pyoderma gangrenosum, perianal fistulae, ulcers |
| Ulcerative colitis | Continuous inflammation of the rectum and large bowel; risk of toxic megacolon | Aphthae, pyoderma gangrenosum, vasculitis, erythema nodosum, fissures |
| Pancreatitis | Abdominal pain, nausea, vomiting, diarrhea | Cullen sign, Grey Turner sign, panniculitis |
| Scurvy | Gingivitis, gradual GI blood loss resulting in anemia | Perifollicular purpura, corkscrew hairs, conjunctival hemorrhage |