Background: Microscopic colitis is a common cause of chronic watery non-bloody diarrhoea. Two major subtypes have been described, collagenous colitis (CC) and lymphocytic colitis (LC). Reported incidence rates differ markedly even between comparable countries and centres such as between the region Skåne in Sweden and Zealand in Denmark. A thorough comparison of the incidence, awareness, diagnostic strategy, endoscopic activity, histopathological assessment, population characteristics including age distribution, autoimmune diseases, smoking and medicines utilization in the two neighbour regions could help assess possible explanations of the different incidence rates.
Methods: Consecutive patients diagnosed with LC and CC were prospectively identified in the Departments of Pathology in the two regions during the years 2011–15. Putative factors affecting the incidence rates were identified in the literature and compared across the two regions.
Results: The incidence of CC changed from 5.4 to 7.5 in 2011–15 in Skåne and from 15 to 15.3 in 2010–15 in Zealand. The incidence of LC changed from 2.5 to 5.1 and from 9 to 12.4, respectively. At the end of 2015 Skåne had 1.3 million inhabitants and Zealand had 0.8. The family doctor appraisal of MC, the number of large bowel endoscopies, the incidence of coeliac disease, diabetes mellitus, thyroid disease, rheumatoid arthritis and the use of MC risk medication in particular and medication in general was compared across the two regions. An inter-observer variation study on the pathology assessment was performed.
Conclusions: The incidence rates for CC and LC differ substantially between the neighbour regions Zealand and Skåne. These differences may in part be explained by differences relating to awareness, diagnostic work out and risk factors.