Lymphoplasmacytic enteritis (LPE)
Idiopathic LPE is the most common histopathological form of idiopathic IBD that can be associated with mild inflammation up to severe infiltration. LPE is characterized by a mucosal infiltrate of lymphocytes and plasma cells (Figure 9.8).
However, there are numerous other causes of lymphoplasmacytic infiltration of the SI, which must be excluded before a diagnosis of LPE can be confirmed. Furthermore, although LPE is most commonly reported, the lymphoplasmacytic inflammation may affect other regions of the GI tract, causing lympho- plasmacytic gastritis and /or colitis.Pathogenesis
Idiopathic LPE is believed to reflect immune dysregulation and loss of tolerance to the enteric flora (see above). Specific alterations in immune cell populations in canine LPE have been documented, including increases in LP T-cells (especially CD4+ cells), IgG+ plasma cells, macrophages, and granulocytes. In cats, there is a marked up-regulation of MHC class II molecule expression. Increased concentrations of acute phase proteins (e.g., C-reactive protein) and marked alterations in cytokine mRNA patterns have been documented in canine LPE.30 Increased expression of Thl (IL-2, IL-12, and IFN-γ), Th2 (IL-5), proinflammatory (TNF-α), and immunoregula- tory (TGF-β) cytokines has been documented, indicating that the mucosal immune response is upregulated in canine LPE.
Clinical signs
Clinical signs of LPE include diarrhea and weight loss. Also, chronic vomiting may be the predominant sign, especially in cats. LPE typically affects older animals, and the disease is uncommon (but not impossible) in individuals less than two years of age. Severe LPE is especially prevalent in German Shepherds, Shar Peis, Norwegian Lundehunds, and pure-bred cats. A very severe form of LPE (immunoproliferative disease), which often causes PLE, is recognized in Basenjis (see 9.2.5).52 PLE, with or without concurrent PLN, has also been described in Soft-coated Wheaten Terriers (see 9.2.6).53
Diagnosis
The approach to diagnosing LPE is the same as for any other form of IBD (see above). Histopathological changes do not only include the presence of increased numbers of lymphocytes and plasma cells, but also architectural disturbances (see Table 9.4).
Complete or partial villus atrophy may be present, while villus fusion and crypt abscessation may be noted in severe cases. The distinction between severe LPE and alimentary lymphoma is sometimes difficult, and discrepancies may exist between endoscopic biopsies and post-mortem examinations of the same patient. It is likely that such discrepancies arise either because both conditions are present concurrently in the GI tract or because low-grade lymphoma is initially misdiagnosed. Clonality studies would help resolve this dilemma and aid in the recognition of low grade lymphoma, but are not widely available. Alternatively, it has been hypothesized that prolonged intestinal inflammation may ultimately transform into lymphoma.Treatment and prognosis
The treatment of LPE is the same as for idiopathic IBD (see above). First-line treatment usually involves dietary manipulation. Metronidazole may be effective alone in mild cases, especially in cats, with immunosuppression being reserved for cases that do not respond or for very sick animals. The prognosis for severe LPE is guarded, but some patients respond dramatically and can ultimately be weaned off all medications. Other cases, however, require persistent low dosage maintenance therapy.
9.2.7