Collagenous Colitis
Definition
- Colorectal disease characterized by a thickened subepithelial collagen layer
Alternate/Historical Names
- Microscopic colitis
- Used by some to refer to both lymphocytic and collagenous colitis, while to others it refers to only lymphocytic colitis
Diagnostic Criteria
- Thickened apical subepithelial collagen layer
- Irregular collagen deposition
- Ragged, spiculated deep edge
- Surrounds and entraps capillaries, fibroblasts and inflammatory cells
- Usually at least 15-20 microns thick
- Frequently up to 50 microns
- Normal thickness is 5-7 microns
- Trichrome stain is useful for demonstration of layer
- Below normal basement membrane
- Demonstrable as type I and III collagen while normal basement membrane is type IV
- Basement membrane remains intact and of normal thickness
- Localized to apical (luminal) region
- Does not surround crypts
- Increased intramucosal chronic inflammatory cells
- Increased lymphocytes and plasma cells in lamina propria
- Increased eosinophils and mast cells may be seen in lamina propria
- Surface mucosa may detach
- Overt ulceration unusual but may occur
- Increased intraepithelial lymphocytes
- Frequently fewer (10-20 / 100 enterocytes) than seen in lymphocytic colitis
- Normal is 5 / 100
- T cell phenotype
- Occasional neutrophils up to cryptitis may be seen in up to 30% of cases
- Infrequently crypt abscesses are prominent
- If present, infection and inflammatory bowel disease must be ruled out
- Multinucleated giant cells may be seen
- Located immediately below the thickened collagen layer
- Frequently fewer (10-20 / 100 enterocytes) than seen in lymphocytic colitis
- No significant crypt distortion
- Mild crypt irregularity has been described in 8% of cases
- May be variably distributed in colon
- A single normal biopsy does not rule out the disease
- Some biopsies may show only the chronic inflammatory infiltrate
- Involvement usually more extensive in right colon
- Terminal ileum may be involved by intramucosal lymphocytosis and occasionally collagen deposition
- Normal levels reported from 2-8 T cells / 100 enterocyte
- Collagenous ileitis can rarely occur in the absence of colorectal disease (O'Brien 2011)
- Rare cases described with superficial ulceration or pseudomembranes
- Lymphocytic colitis and collagenous colitis have been proposed to be related
- They share an identical chronic inflammatory pattern and are distinguished only by the presence of a thickened collagen layer only in the latter
- Cases are reported showing change from one to the other on sequential biopsies
- Collagen deposition in collagenous colitis may be patchy, making interpretation of such observations difficult
- Female:Male ratios originally reported as different
- More recent studies find similar ratios of approximately 1-5:1 F:M (Kao 2009)
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting/updates: 11/11/09, 12/3/09, 10/25/10, 11/11/11, 1/28/12
