To understand clearly extraintestinal diseases
Certain intestinal diseases have symptoms that appear concurrently in other systems of the body, but the bowel diseases themselves are not extraintestinal.  


  Extraintestinal manifestations of inflammatory bowel disease are prevalent in both ulcerative colitis and Crohn's disease. The most common manifestations involve the musculoskeletal and dermatologic systems. Other manifestations involve the hepatopan-creatobiliary system (eg, primary sclerosing cholangitis) as well as the ocular, renal, and pulmonary systems1. 


One of the key differences between extraintestinal manifestations and comorbid conditions (though seemingly not a necessity, the article cites primary sclerosing cholangitis as an counterexample) is that the extraintestinal effects will subside once the disease of the bowel is treated.

1 Levine, J.S., Burakoff, R. (2011). Extraintestinal Manifestations of Inflammatory Bowel Disease. Gastroenterol Hepatol (NY), 7(4), 235–241.