What are the key clinical features that differentiate Crohn's disease from Ulcerative Colitis in a primary care setting?

In a primary care setting, while definitive diagnosis of inflammatory bowel disease (IBD) is made in secondary care, key clinical features can help differentiate between Crohn's disease and Ulcerative Colitis (UC) ¹,².

• Location and Pattern of Inflammation: Crohn's disease can affect any part of the gastrointestinal tract, from the mouth to the anus, and is characterized by discontinuous inflammation or ulceration, often with 'skip lesions' and rectal sparing ¹ (Brown, 1999). In contrast, Ulcerative Colitis typically involves continuous inflammation limited to the colon and rectum, often starting in the rectum and extending proximally ² (Brown, 1999).
• Depth of Inflammation: Crohn's disease involves transmural inflammation, meaning it affects all layers of the bowel wall (Brown, 1999). Ulcerative Colitis, however, is characterized by superficial inflammation, primarily affecting the mucosa (Brown, 1999).
• Perianal Disease: The presence of perianal disease, such as abscesses and fistulae, is a common feature of Crohn's disease and can be evaluated with pelvic MRI ¹ (Brown, 1999). These manifestations are not typically associated with Ulcerative Colitis.
• Rectal Bleeding: While both conditions can cause bloody diarrhoea, visible blood in stools is a more prominent and consistent feature of Ulcerative Colitis, particularly in moderate to severe cases, and is a key indicator in severity assessment tools like the Truelove and Witts' index ²,⁴. Bloody diarrhoea can also occur in Crohn's disease ¹.
• Complications: Crohn's disease is often associated with complications such as strictures, fistulae, and abscesses ¹. In Ulcerative Colitis, there is a specific risk of toxic megacolon, particularly if anti-diarrhoeal drugs or opiate analgesia are used when the diagnosis is uncertain or during a flare-up ¹,².

It is crucial to note that if Crohn's disease or Ulcerative Colitis is suspected, an urgent referral to secondary care (paediatric or adult gastroenterologist) is required for confirmation of diagnosis and specialist management ¹,². Emergency hospital admission is indicated if the person is systemically unwell with symptoms such as bloody diarrhoea, fever, tachycardia, or hypotension ¹,².