Adherent-invasive Escherichia coli (AIEC), more common in people with CD, have the ability to make strong biofilms compared to non-AIEC strains correlating with high adhesion and invasion indices of neutrophils and the ability to block autophagy at the autolysosomal step, which allows for intracellular survival of the bacteria and induction of inflammation. Inflammation drives the proliferation of AIEC and dysbiosis in the ileum, irrespective of genotype. AIEC strains replicate extensively inside macrophages inducing the secretion of very large amounts of TNF-α.Mouse studies have suggested some symptoms of Crohns disease, ulcerative colitis, and irritable bowel syndrome have the same underlying cause. Biopsy samples taken from the colons of all three patient groups were found to produce elevated levels of a serine protease. Experimental introduction of the serine protease into mice has been found to produce widespread pain associated with irritable bowel syndrome, as well as colitis, which is associated with all three diseases. Regional and temporal variations in those illnesses follow those associated with infection with the protozoan Blastocystis.The "cold-chain" hypothesis is that psychrotrophic bacteria such as Yersinia and Listeria species contribute to the disease. A statistical correlation was found between the advent of the use of refrigeration in the United States and various parts of Europe and the rise of the disease.There is also a tentative association between Candida colonization and Crohns disease.Still, these relationships between specific pathogens and Crohns disease remain unclear. Environmental factors
The increased incidence of Crohns in the industrialized world indicates an environmental component.
The arthritis may also involve the spine, leading to ankylosing spondylitis if the entire spine is involved, or simply sacroiliitis if only the sacroiliac joint is involved. The symptoms of arthritis include painful, warm, swollen, stiff joints, and loss of joint mobility or function.Crohns disease increases the risk of osteoporosis or thinning of the bones. Individuals with osteoporosis are at increased risk of bone fractures. Dermatological
Crohns disease may also involve the skin, blood, and endocrine system. Erythema nodosum is the most common type of skin problem, occurring in around 8% of people with Crohns disease, producing raised, tender red nodules usually appearing on the shins. Erythema nodosum is due to inflammation of the underlying subcutaneous tissue, and is characterized by septal panniculitis.Pyoderma gangrenosum is a less common skin problem, occurring in under 2%, and is typically a painful ulcerating nodule.Clubbing, a deformity of the ends of the fingers, may also be a result of Crohns disease. Other very rare dermatological manifestations include: Pyostomatitis vegetans, Psoriasis, Erythema multiforme, Epidermolysis bullosa acquista (described in a case report), and Metastatic CD (the spread of Crohns inflammation to the skin). It is unknown if Sweets Syndrome is connected to Crohns disease.Neurological
Crohns disease can also cause neurological complications (reportedly in up to 15%). The most common of these are seizures, stroke, myopathy, peripheral neuropathy, headache, and depression.Central and peripheral neurological disorders are described in patients with IBD and include peripheral neuropathies, myopathies, focal central nervous system defects, convulsions, confusional episodes, meningitis, syncope, optic neuritis, and sensorineural loss.