Crohn’s disease (CD) is a type of Inflammatory Bowel Disease characterized by inflammation involving discrete segments of any part of the gastrointestinal tract from mouth to anus. Crohn’s disease should be suspected in patients presenting with features of long-standing diarrhea, abdominal pain and weight loss. Perianal pain or pus discharge especially in a young patient frequently warrants investigation for Crohn’s disease. As with Ulcerative Colitis, CD also usually presents in the second or third decade of life.

What are the risk factors for CD?

Most of therisk factors discussed for Ulcerative Colitis hold true also for CD.  It is thought to be caused by an interplay between the host genetics, gut microbiota and other environmental stressors. Mycobacterium Paratuberculosis infection has been implicated as a causative factor in some studies, hence some patients may show a temporary treatment response to anti tubercular drugs. Genetic characterization of CD patients has implicated an abnormal NOD2/CARD15 gene locus in up to 30% of patients. Smoking increases risk for CD unlike in UC.

Clinical Presentation

CD frequently presents in second or third decade of life with no specific sex predilection. The diagnosis of CD usually occurs late as symptoms maybe subtle at the disease onset and hence are neglected or disease not sought after. In up to 25% of patients, the disease comes to attention after 2-3 years of onset. This is unlike UC which usually comes to early attention.
Abdominal pain is frequently the most common presentation in CD. Pain maybe colicky or sustained. Most patients have severe impairment in quality of life due to frequent pain episodes and often warrants the use of analgesics. Many patients complain of an increase in pain after eating and hence severely reduce their diet and suffer from weight loss. Weight loss and muscle wasting (cachexia) is also attributable to the underlying chronic inflammation which produces a catabolic state and reduces hunger (anorexia). Severe and long segments of small intestinal involvement also impairs absorption of nutrients and contributes to weight loss.
Diarrhoea is another frequent presentation of CD. Volumes of loose stools maybe large when small intestine is involved (more common) or small volume when colon is involved (less common). Episodes of loose stools are associated with abdominal pain and frequently occur at night.
Patients who have involvement of anal canal and tissues around anal canal (perianal CD)may present with symptoms of either perianal pain, pus or bloody discharge, boggy swelling or spiking fever with chills.

How is CD diagnosed?

As CD can affect any part of the intestine, the diagnostic modality used depends on the Clinician’s assessment as to which part is likely to be involved.
CD most commonly affects the ileo-caecal region (junction of the small and large intestine), hence Colonoscopy is frequently the first test recommended as it is easily available and not technically challenging.

Clinician might also recommend doing an upper gastrointestinal endoscopy (oral gastroduodenoscopy) to see for the esophagus, stomach and the upper duodenum (first part of small intestine).
Guidelines recommend evaluating the entire length of the digestive tract prior to initiation of therapy for CD, hence frequently varying combinations of these tests maybe recommended by your doctor after diagnosis.

How does CD manifest?

CD usually manifests in either of three major presentations. Combinations of any or all individual morphologies is also frequently seen.

1. Ulcerative disease
2. Stricturing disease
3. Perianal disease

Ulcerative disease is characterized by development of different types of ulcers along any segment of the gastrointestinal tract. Disease often starts with small punched out ulcers with surrounding redness called as apthous ulcers. As the disease progresses, these ulcers coalesce to form stellate shaped ulcers and later linear or serpiginous ulcers. Patients with ulcer predominant disease usually present with diarrhea, abdominal pain and nutrient deficiencies.
As the ulcers go on increasing in extent, they tend to involve deeper layers of intestine and can cause perforation and abscess formation (collection of pus) in the abdominal cavity. Predominant presentation in these cases is persistent pain and fever spikes.

As the disease tries to heal, stricture formation can occur due to excessive deposition of fibrous tissue. This leads to narrowing of affected intestinal lumen. When this occurs, patients have symptoms of intestinal obstruction and may present with abdominal distension, severe constipation and recurrent vomiting.
Perianal disease usually presents early and is often associated with more severe underlying disease. Symptoms are perianal pain, swelling, pus or blood discharge and fever with chills.

Is a biopsy always diagnostic in CD?

CD is a transmural disease, meaning that it tends to involve all the layers of the intestine. Characteristic pathological features of CD include granulomas (typical collection of specialized cells) and chronic inflammatory cells. As a biopsy can only access a superficial part of the intestinal wall (mucosa); it is very likely to miss the typical features of CD. Hence only 10% of the biopsies intended for CD show all classical features. Surgical specimens, wherein entire thickness of the affected intestinal segment is available, are more likely to yield conclusive results. But surgery is never indicated only for diagnosis of the disease.
Hence in most cases, diagnosis of CD is based on the clinicians judgment and results of various endoscopic and imaging tests and seldom on biopsy. A negative biopsy thus does not rule out CD.