Pattern of Disease

In ulcerative colitis, the classical teaching is that the inflammation is always continuous with the rectum being primarily involved. Topographically, UC is classified as distal colitis referring to colitis confined to the rectum, recto-sigmoid, left sided when the disease extends to the splenic flexure, extensive colitis if the disease extends to the hepatic flexure. Pan-colitis is a term used when the inflammatory process involves the entire colon. There are, however, two exceptions to the rule.

Firstly, there are various reports suggesting that UC can be associated with relatively uninvolved patches including rectal sparing, thus giving the false impression of discontinuous disease and therefore suggesting CD in a genuine case of UC [38]. This is especially true in the paediatric age group where it has been shown that children may present initially with relative or complete rectal sparing or even patchy disease. Thus, non-classical features of UC in the paediatric age group do not exclude its diagnosis [44]. The patchiness of inflammation has also been described and recognised in some cases of left-sided UC where there is an area of inflammation in the caecum ("caecal patch"), in the periappendiceal mucosa or involving the appendix [45]. Secondly, it is important to remember that some workers suggest that the mucosa in a long standing UC may go back to normal with or without treatment with 5-Amiosalicylic Acid [46, 35].

In CD, the inflammation is classically patchy, transmural and may affect any part of the gastrointestinal tract. It is usually defined by its location such as terminal ileitis, colonic, upper gastrointestinal etc., or by the pattern of the disease inflammation, which could be infiltrating or stricturing. These variables are combined in the Vienna classification, which veers from the original anatomic classification of CD. The Vienna classification is a simple and objective classification of Crohn's disease and encompasses different variables such as age at onset, location and disease behaviour [47]. Application of the Vienna classification has demonstrated that in CD the process changes with time and 80% of inflammatory diseases ultimately evolve into a stricturing or penetrating pattern and about 15% undergo a change in anatomical location (Table 1) [48]. A new classification is under consideration following the 2005 World Congress at Montreal and it is envisaged to be a combined clinical, molecular and serological classification for IBD [49].

Table 1. The Vienna classification of Crohn's disease [47,48]

Age at diagnosis

A1

<40 years

A2

>40 years

Location

L1

Terminal ileum

L2

Colon

L3

Ileocolon

L4

Upper gastrointestinal

Behaviour

B1

Non-stricturing non-

penetrating

B2

Stricturing

B3

Penetrating

The Impact of CPC on the Diagnosis

As we discussed earlier, CPCs are the best forum [50] for discussing cases, corroborating findings and coming to a definitive diagnosis. In many hospitals, however, CPCs are not held regularly. It has been shown that when discussing gastrointestinal cases at CPCs, in over 40% of cases there is a change of management following a change in diagnosis [50]. A recent study was carried out by our group with the use of a combined clinicopathological form with sufficient information, clinical investigations and endo-scopic findings along with a pattern based report by the pathologist. We suggest using those forms in places where CPCs are not regularly held as the use of this form could significantly increase the range of accurate diagnoses of UC or CD. The study showed that without regular CPCs, but with the use of regular available information, only approximately 60% of cases of IBD are accurately diagnosed as CD or UC. However, the use of this form has raised the possibility of a definite diagnosis to approximately 77%, which is slightly inferior to the 82% of CPCs and we concluded that in the absence of regular CPCs, it definitely shows great potential and is the next best substitute [51]. A reproduction of the form, which contains most of the information the pathologist expects and is usually necessary for a definitive diagnosis, is shown in Fig. 1. Histological diagnosis of any condition, by and large, is greatly dependent on the availability of adequate and accurate clinical information, and this greatly holds true for the histological examination of tissues for IBD [52]. Providing adequate information in blank form is often difficult and lacks uniform application. We have tried to work around this problem via this form and we suggest that it, or a modified version, will be a simple way to overcome a lack of CPCs. It will also help the histopathologist in coming to a diagnosis or narrowing the list of differential diagnoses. This form also uses the standard definition of histological terms and gives a list of more likely diagnoses, which is essential not only in understanding and managing different patients, but is indispensable for proper auditing, research and the communication of findings between the pathologist and clinician across different specialty institutions [53, 43].

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