AN IMPORTANT CAUSEOF INTESTINAL PROTEIN LOSS
WHAT IS A PROTEIN-LOSING ENTEROPATHY?
“Protein-losing Enteropathy” is a fancy way of saying there is something wrong with the intestine such that protein is being lost from the body through the intestine. This is a serious problem as the body’s proteins are not easily replaced and the only way to replace them involves the absorption of protein constituents (the amino acids that make up proteins) from the intestine. If the intestine is actually leaking nutrients out instead of absorbing them in, the result is a nutritional disaster.
The main protein which one cannot afford to lose is called “Albumin.” This protein normally is produced by one’s liver and circulates in the bloodstream acting as a carrier for biochemicals that require transport but cannot actually dissolve in blood. Albumin can be considered sort of a mass transit system in the bloodstream, a bus or subway, if you will, carrying important biochemicals from one place to another.
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 protein.
There are four chief cases of protein-losing enteropathy:
Inflammatory Bowel Disease
Histoplasmosis (a fungal infection)
The first three conditions are reviewed elsewhere and will not be discussed here.
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. Lymph also consists of fluid which collects from the tissues and shunts into actual vessels 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. 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.
WHAT DOES ONE SEE AT HOME?
Weight loss is the most consistent sign along with chronic diarrhea, vomiting, and fluid accumulation in the abdomen creating a bloated appearance.
HOW DO WE MAKE A DIAGNOSIS?
In most cases, an obviously sick 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.
Low Lymphocyte Count
Animals with lymphangiectasia have lymphocytes rolling out their lacteals and into their intestine. The low blood lymphocyte count is so consistent with lymphangiectasia that it is difficult to make this diagnosis if this finding is not present.
Cholesterol is part of the lymph fluid being lost.
Low Albumin Level
Low blood albumin level is the most consistent finding in lymphangiectasia, though it is possible to have lymphangiectasia in a small portion of the intestine only and still maintain a normal albumin level.
There are only four ways a patient can develop a low albumin level.
A protein-losing enteropathy
Glomerular disease (such as glomerulonephritis) in which albumin is lost through diseased kidneys
Reduced albumin production in the liver due to liver failure
Serum leakage through extreme skin damage (such as third degree burns)
These conditions can be easily ruled out one by one. It is obvious if there are third degree burns present. If there are none, a routine urinalysis will indicate if there is significant protein loss in the urine and if glomerular disease should be pursued. A liver function test such as a bile acids test will indicate whether or not there is liver failure latently present. If none of these three conditions are present, then there must be a protein-losing enteropathy.
As mentioned, there are four likely causes of protein-losing enteropathy. To distinguish them and initial the correct treatment, an intestinal biopsy is essential. This can be done surgically or via endoscopy but rational treatment is not possible without a tissue sample.
TREATMENT AND WHAT TO EXPECT
The first step in treatment is to address the underlying cause. In most cases of lymphangiectasia, the underlying cause involves inflammation and most treatment of lymphangiectasia involves suppression of inflammation.
Medications such as prednisone, and/or azathioprine are commonly used, especially if inflammatory bowel disease is present.
The second step in treatment is dietary though success has been mixed. Traditionally, rather nasty tasting Medium Chain Triglycerides have been used in lymphangiectasia treatment. Triglycerides (a fancy word for “fats”) are very long molecules. Some are longer than others. The more usual dietary fats are called “Long Chain Triglycerides” and, when absorbed into one’s body, must be repackaged into fat globules called “chylomicra” and are normally absorbed into the lymph vessels. In lymphangiectasia, we want to reduce the pressure in the lymph vessels. We want less lymph. The idea was that if the patient ate shorter fat chains, the fats could be absorbed right into bloodstream directly and bypass the lymph system altogether.
Whether or not this actually happens is still a matter of controversy but the addtion of Medium Chain Triglycerides (or “MCT’s”) in conjunction with a low fat diet are common recommendations in the therapy of lymphangiectasia.
Other treatments include the use of diuretics (such as furosemide) to help increase urination and ultimately reduce fluid accumulation in the chest or abdomen. Actual tapping of the body cavity and suctioning the fluid affected may be needed periodically.
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.