Collagenous colitis is a form of watery diarrhea associated with the thickening of the subepithelial collagen of the colon [1]. It usually occurs in the absence of underlying disease, and only rarely has it been associated with connective tissue disorders [2-4]. We report the first case of systemic lupus erythematosus accompanied by collagenous colitis.

A 47-year-old woman with systemic lupus accompanied by myositis, interstitial lung disease, and cytopenias developed severe watery diarrhea. Her stool volumes ranged from 900 to 1500 mL/d. Stool specimens were negative for occult blood, leukocytes, bacterial pathogens, Clostridium difficile toxin, parasites, mycobacteria, fungi, and viruses. Sigmoidoscopy showed normal colonic mucosa with mild edema. Examination of a rectal biopsy specimen showed a thickened subepithelial collagen band varying in width from 10 to 50 microns (normal, 4.6 to 6 microns), consistent with collagenous colitis. Congo red stains for amyloid were negative. The C3 level was 67 mg/dL (normal, 83 to 177 mg/dL), and the C4 level was 16.3 mg/dL (normal, 15 to 45 mg/dL). She was treated with loperamide and prednisone, and her diarrhea subsequently resolved.

Collagenous colitis has rarely been associated with seronegative polyarthritis [1, 2], discoid lupus [2], scleroderma [3], and the calcinosis cutis syndrome [4] but to our knowledge has not previously been reported with systemic lupus erythematosus. Our patient had lupus and developed watery diarrhea secondary to collagenous colitis, which appeared to respond to antimotility agents and corticosteroid therapy. An extensive workup showed no infectious cause of her diarrhea. Although the low complement values suggest immune complex formation, previous studies have shown no staining for immunoglobulins or complement (or electron-dense deposits suggesting antigen-antibody complexes) in the subepithelial collagen layer in collagenous colitis [5]. Collagenous colitis should be included in the differential diagnosis of watery diarrhea in patients with systemic lupus erythematosus.