Terminology for the diagnosis of colitis.

D uring the past few years, there has been a ‘‘proliferation’’ of terms used for the diagnosis of colitis. This reflects the fact that colitis is a complex condition, but the different terminologies are often a source of disagreement between pathologists and clinicians and, at times, can result in misdiagnosis. ‘‘Microscopic colitis’’, ‘‘indeterminate colitis’’, and ‘‘non-specific colitis’’ are terms frequently used but not always clear to the clinician. Therefore, it is reasonable for the clinician to abide by the dictum ‘‘when I receive a diagnosis of non-specific colitis, I prescribe a non-specific treatment’’. However, the clinician may also have insufficient knowledge. The major problem is a vague definition or lack of definition. Non-specific colitis is an acceptable diagnosis when clinical information is lacking. The microscopic picture is characterised by an increase in inflammatory cells beyond what would be expected physiologically in the corresponding anatomical sites. The cellular infiltrate is predominantly chronic, with the absence of architectural distortion and multiple basal lymphoid aggregates or plasma cells immediately above the muscularis mucosae. Crypts may show an increase in mitoses and slight irregularity in shape. Lack of sufficient clinical data or distinctive pathological features precludes further classification into specific aetiological types of colitis. Such a pattern can be seen in resolving infections, complicated diverticular disease, drug induced colitis, and bile salt malabsorption, but may also be seen in Crohn’s disease (CD). However, it is impossible to make a positive diagnosis of CD in these circumstances, although in a patient with known CD the lesions may represent local involvement. However, a more precise diagnosis by the pathologist is often possible when clinical information is available. In such a situation, the clinician should decide on the final diagnosis or provide the clinical data. The term ‘‘microscopic colitis’’ was introduced to describe lesions found in patients with chronic watery diarrhoea of unknown origin. Later, microscopic colitis was proposed as an umbrella term for two conditions (lymphocytic colitis (LC) and collagenous colitis (CC)) and defined as a condition in which there was histological but no endoscopical or radiological abnormality. 5