Introduction
Protein-losing enteropathy (PLE) is a syndrome in which there is excessive loss of proteins into the lumen of the gastrointestinal tract (Willard et al. 2000). PLE is identified when hypoalbuminemia occurs because the loss of albumin cannot be compensated by liver synthesis (Dossin and Lavoue 2011).
In dogs, PLE has been described extensively, and certain breeds (Norwegian Lundehund, Basenji, Soft Coated Wheaten Terrier, German Shepherds, Rottweilers, and Yorkshire Terriers) appear to be at increased risk for PLE (Littman et al. 2000; Lecoindre, Chevallier, and Guerret 2010; Simpson and Jergens 2011; Equilino et al. 2015). Commonly reported causes of PLE include alimentary lymphoma, chronic intussusception, hookworm infestation, inflammatory bowel disease (IBD), or lymphangiectasia (Murphy et al. 2003). Food hypersensitivity reactions are also a documented cause of enteropathy and can be occult or associated with clinical signs of varying severity, including PLE. However, any disease causing gastrointestinal tract inflammation, infiltration, congestion, or bleeding can result in PLE (Hall and German 2010).Identifying gastrointestinal tract disease in a dog with hypoproteinemia and ruling out cutaneous protein loss, renal protein loss, and hepatic insufficiency leads to a diagnosis of PLE (Willard et al. 2000). Enteric loss of protein can occur by means of several mechanisms, including increased mucosal permeability to proteins, lymphatic obstruction, or mucosal erosion and has a greater effect on serum concentrations of proteins that typically have a low catabolic rate (Vaden et al. 2000).
Lymphangiectasia is a condition characterized by dilatation of the lymphatic vessels and leakage of lymph from the villi or from deeper portions of the intestinal wall into the intestinal lumen (Dossin and Lavoue 2011). The leakage of proteins, lipids, and lymphocyte-rich lymph into the intestinal lumen is responsible for the protein loss (i.e., PLE) and lymphopenia sometimes is observed. Lymphangiectasia may be primary (idiopathic or congenital) or secondary to other diseases that increase the hydrostatic pressure in the lymphatic vessels of the gastrointestinal tract due to infiltrates (e.g., IBD or alimentary lymphoma).