Lymphocytic-plasmacytic enteritis (LPE) is the most common form of idiopathic inflammatory bowel disease. It is characterized by a mucosal infiltrate of lymphocytes and plasma cells. However, there are numerous other causes of lymphocytic-plasmacytic infiltration of the small intestine, including enteric pathogens, bacteria, and Toxoplasma organisms. All such underlying causes must be excluded before a diagnosis of idiopathic lymphocytic-plasmacytic enteritis is confirmed.
Idiopathic lymphocytic-plasmacytic enteritis is believed to reflect immune dysregulation, and the spectrum of severity ranges from mild to severe infiltration. Alterations in immune cell populations in canine lymphocytic-plasmacytic enteritis have been documented, including increases in lamina propria T cells (especially CD4+ cells), lgG+ plasma cells, macrophages, and granulocytes IM
Increased concentrations of acute-phase proteins (e. g., C-reactive protein), which normalize after treatment, have been documented in canine lymphocytic-plasmacytic enteritis. M Marked alterations in cytokine patterns also were recently documented in canine lymphocytic-plasmacytic enteritis, with increased expression of Th 1 (IL-2, IL-12, and IFN-gamma), Th2 (IL-5), proinflammatory (TNF-alpha), and immunoregulatory (TGF-beta) cytokines. These studies confirm that the mucosal immune response is upregulated in canine inflammatory bowel disease.
Clinical signs of lymphocytic-plasmacytic enteritis include diarrhea and weight loss, but these are not pathognomonic. Chronic vomiting may be the predominant sign, especially in cats. Lymphocytic-plasmacytic enteritis is prevalent in German shepherds, Shar Peis, and purebred cats, and in dogs it often causes a protein-losing enteropathy. Severe lymphocytic-plasmacytic enteritis (immunoproliferative disease) is recognized in basenjis. Protein-losing enteropathy with or without concurrent protein-losing nephropathy has also been described in soft-coated wheaten terriers. Lymphocytic-plasmacytic enteritis typically affects older animals; it is uncommon (but not impossible) in individuals less than 2 years of age.
The approach to diagnosis of lymphocytic-plasmacytic enteritis is the same as for any chronic enteropathy, although definitive diagnosis ultimately depends on documentation of characteristic histopathologic changes in the absence of an underlying cause. Such changes include the presence of increased numbers of lymphocytes and plasma cells in association with architectural disturbances. Complete or partial villus atrophy may be present, and villus fusion and crypt abscessation may be noted in severe cases. The distinction between severe lymphocytic-plasmacytic enteritis and alimentary lymphoma is sometimes difficult, and discrepancies may arise between endoscopic biopsies and postmortem examination of the same patient. It is hypothesized that such discrepancies arise because the two conditions may be present concurrendy in the small intestine, because prolonged intestinal inflammation may ultimately result in transformation to lymphoma, or because low-grade lymphoma is initially misdiagnosed.
Another major concern is the criteria by which a diagnosis of lymphocytic-plasmacytic enteritis is made. In this regard, major discrepancies exist in interpretation of intestinal biopsies by different histopathologists. Interpretation of the degree of inflammation is subjective; inflammation may be patchy, and the presence of edema (due to hypoproteinemia) may make cell density difficult to assess. Furthermore, discrepancies exist between gross endoscopic and histologic findings, and proximal endoscopic biopsies may not be representative. Attempts have been made to standardize interpretation by using grading schemes; those that assess morphologic abnormalities in conjunction with changes in cellularity are most appropriate.
Treatment and Prognosis
The treatment of lymphocytic-plasmacytic enteritis is that outlined for idiopathic inflammatory bowel disease above. First-line treatment usually involves dietary manipulation and metronidazole. The prognosis for severe lymphocytic-plasmacytic enteritis is guarded. Some patients respond dramatically and can ultimately be weaned off all medication; other cases, however, require persistent, low-dose maintenance immunosuppressive therapy.