Seasonal Variation of Duodenal Intraepithelial Lymphocytosis.

The increase of intraepithelial lymphocytes in architecturally normal duodenal mucosa is commonly referred to as duodenal intraepithelial lymphocytosis (DIL). The characteristic appearance of DIL corresponds with Marsh grade 1, that is, normal or mild increase in lamina propria inflammation of the duodenal mucosa, with no crypt hyperplasia or villous atrophy.1 Approximately 11% of DIL patients harbor clinical and serologic features suggestive of gluten sensitivity.2 An additional 2% of patients with DIL harbor concomitant microscopic colitis.3Helicobacter pylori gastritis may contribute to another 10%-15% of DIL, which may resolve following eradication of H pylori.4 In the majority of cases with DIL, however, its underlying cause has remained unknown.1 A study of the seasonal variations in the occurrence of DIL may provide additional clues about its yet unknown etiology.