LYMPHANGIECTASIA: AN IMPORTANT CAUSE OF INTESTINAL PROTEIN LOSS
WHAT IS A PROTEIN-LOSING ENTEROPATHY?
Albumin, by being the most prevalent blood protein, also is responsible for actually keeping water in one’s bloodstream. When water cannot be held within the vasculature, it leaks out causing fluid accumulation in tissue (i.e. edema) or in within the chest or abdomen (i.e. effusion).
Of course, in a protein-losing enteropathy, other proteins are lost, too. Antibodies, proteins of blood clotting, enzymes, etc. all leak out the intestine and are forever lost in the feces that exits the body.
The body tries hard to maintain its albumin level by extracting protein from other sources (like muscle), and having the liver make albumin from the components of these other proteins. This may help maintain a workable amount of albumin in the bloodstream but it comes at the expense of muscle tissue and other working proteins.
There are several described causes of protein-losing enteropathy:
We will limit our discussion to lymphangiectasia.
WHAT IS INTESTINAL LYMPHANGIECTASIA?
Lymph is a fluid that circulates through the body similar to the way blood does; though blood is pumped actively through the body by the heart while lymph is pumped passively via the normal muscle activity of the body. Lymph consists of cells called “lymphocytes,” which are cells of the immune system as well as the fluid which collects from the tissues and shunts into lymphatic vessels which are similar to veins.
The word “lymphangiectasia” means “dilated lymph vessels.” In the intestinal tract, lymphangiectasia is usually caused by some kind of inflammation which puts back pressure on the lymph vessels leading them to dilate. Lymph flow may be blocked by the inflammatory events in the intestine or local structures.
Lacteals are special lymph vessels in the intestinal tract designed to absorb nutritional fats. The intestine is able to absorb our nutrients through small finger-like structures called "microvilli." Lacteals run though the center of the microvilli happily imbibing fats from the food we have eaten. When there is high pressure within the lymph vessels, the tender lacteals burst and instead of absorbing fats, the lymph inside, its cells, fats, and precious proteins are lost. The intestine may be able to reabsorb some of these valuable substances at other sites but if the inflammatory intestinal disease that started the problem in the first place is widespread, the balance may have shifted to nutritional loss rather than gain.
Small terrier breeds, particularly the Yorkshire terrier,
Lymphangiectasia is extremely rare in the cat.
WHAT DOES ONE SEE AT HOME?
Weight loss is the most consistent sign along with chronic diarrhea, vomiting, and, in more advanced cases, fluid accumulation in the abdomen creating a bloated appearance.
HOW DO WE MAKE A DIAGNOSIS?
In most cases, an obviously sick skinny dog is brought to the veterinarian. Sometimes the above classical signs are present but sometimes there is no specific hint of this condition until blood test results are in.
Tissue sampling is necessary to distinguish the intestinal diseases that cause protein-losing enteropathy. With most PLE patients being deficient in albumin, this means they are not in a good position to heal from a surgical biopsy so endoscopy is generally recommended as it is less invasive. With endoscopy a small camera on a long flexible scope travels down the mouth, through the stomach and into the intestine (or retrograde from the anus up past the large intestine and into the lower small intestine) where biopsy samples can be pinched off with a special grabber. The procedure requires general anesthesia but is otherwise low risk and most patients can go home the same day. Often the areas of intestinal disease are patchy and surrounded by large areas of normal intestine so it is important to biopsy the right area. Ultrasound of the abdomen prior to endoscopy is helpful in determining where to sample plus often a few spoons of corn oil or other fat are often fed a few hours prior to biopsy so that dilated lacteals with plump and leaking fat visibly in the best areas for biopsy. Because PLE patients often lose important vitamins and blood clotting factors, blood clotting tests are generally done just prior to endoscopy.
The image above is actually from a human with lymphangiectasia but the concept is the same. Note the large pale areas within the intestinal microvillus shown. These are dilated lacteals. (The small white areas in the layer of cells lining the villi are "goblet cell" which produce mucus. The dilated lacteals are the large expanses of white or lavender underneath the villus lining).
The first step in treatment is to address the underlying cause. In many cases of lymphangiectasia, there is an association with inflammatory bowel disease ("IBD"). Whether or not the IBD is actually causing the lymphangiectasia remains a matter of speculation but anti-inflammatories are often used aggressively in lymphangiectasia patients. Prednisolone has been the traditional immune suppressive medication in this situation but as it causes an increase in water consumption that can contribute to edema, other medications, particularly cyclosporine, have become more popular as it does not have steroid side effects.
Intestinal loss of a body protein called "anti-thrombin III" leads to a tendency to form abnormal blood clots which can lodge in inappropriate places (embolization). As prevention, anti-clotting medications are often used. Aspirin has been traditional but clopidogrel is gaining popularity.
Nutritional management of PLE is a bit tricky. The diet must be especially digestible and high in protein (20-25% protein on a dry matter basis) so as to replace all the protein being lost through the leaky GI tract. Further, the diet should be no more than 15% fat on a dry matter basis (lower for more severely affected patients). Reading a diet label shows percentages on an "as fed" basis, so to compare diets, it is necessary to convert values to a dry matter basis through knowing the moisture content. To see how this is done click here. There are prescription diets available for diseases like this one where fat restriction is crucial. Non-prescription diets are unlikely to meet the above criteria but if you know how to read the food label properly you may be able to find one. Injectable vitamin supplements are likely to be needed.
Severely affected dogs will find even the fat content of the prescription diets too high and may need to begin with what is called an "elemental diet." These are typically made for humans and are powders that can be mixed with water. They are not nutritionally balanced for dogs and can only be used for a few weeks. Alternatively, home cooked diets can be used but a professional veterinary nutritionist should be consulted to get a proper recipe. Again, because of intestinal absorption issues injectable vitamin supplements are likely to be needed. The goal is to eventually return to a standard commercial dog food.
If the underlying condition is treatable then prognosis for lymphangiectasia is good. It should be understood that lymphangiectasia is unlikely to be cured and at best can be managed.
Page last updated: 6/24/2019