My son was diagnosed with Crohn's with only ileitis, by colonoscopy, elevated CRP, anemia , and a few months of diarrhea.
Below is the list of causes of ileitis from the article mentioned in the previous post. Note many are ruled out on the basis of history alone. If you didn't have radiation treatment, it's not radiation enteritis. If you haven't taken lots of NSAIDs like motrin, that's not the cause. Others are ruled out at the time of colonoscopy. It's not backwash ileitis if there's no colonic disease. From my understanding, if the biopsy shows a granuloma, it's Crohn's unless you have systemic TB. If it doesn't show a granuloma, but you have
symptoms and labs that support Crohn's, that's what it is; this was my son's case. Infectious causes generally present differently than Crohn's. Systemic diseases that cause ileitis affect other organs too. Here is the full article if you are interested
http://europepmc.org/articles/PMC2914216
Best wishes.
Selected causes of ileitis
Infectious
Yersinia spp.
Salmonella spp.
Clostridium difficile
Typhlitis
Mycobacterium tuberculosis
Mycobacterium avium
Actinomycosis
Anisakiasis
Cytomegalovirus
Histoplasma capsulatum
Spondyloarthropathies
Ankylosing spondylitis
Reactive arthritis
Arthritis associated with inflammatory bowel disease
Psoriasis with arthritis
Undifferentiated spondylarthropathy
Vascular
Vasculitides
Systemic lupus erythematosus
Polyarteritis nodosa
Henoch-Schönlein purpura
Behçet's disease
Other vasculitides: Churg-Strauss syndrome, rheumatoid arthritis vasculitis,
Wegener granulomatosis, lymphomatoid granulomatosis, giant-cell
arteritis, Takayasu arteritis, thromboangiitis obliterans
Ischemia
Small-bowel neoplasms
Cecal or small-bowel (ileal) adenocarcinoma
Lymphoma
Carcinoid tumor
Lymphosarcoma
Metastatic cancer
Drug-related
NSAID enteropathy
Other drugs: KCL tablets, parenteral gold therapy, oral contraceptives, ergotamine,
digoxin, diuretics, antihypertensives
Infiltrative
Eosinophilic enteritis
Sarcoidosis
Amyloidosis
Other causes
Backwash ileitis due to ulcerative colitis
Endometriosis
Radiation enteritis
KCL—potassium chloride; NSAID—nonsteroidal anti-inflammatory drugs.