Proximal Enteritis (Proximal Duodenitis/Jejunitis, Anterior Enteritis)
Dr. Melissa Mazan
Physical examination. Your veterinarian will want to assess the level of pain, heart rate, dehydration, presence or absence of gut sounds, and your horse's attitude. Horses with either surgical colic or proximal enteritis will both be painful, but surgical colic is often more severely colicky. Horses with surgical colic rarely have a fever, whereas horses with proximal enteritis may occasionally have a fever. Usually there is a complete absence of gastrointestinal sounds. The heart rate is usually above 60 beats per minute. All the fluid backed up in the small intestine results in fluid loss; consequently, your horse will become dehydrated rapidly. The horse's mucous membranes will become toxic – that is, reddened and often darker near the interface with the teeth.
If your horse is very painful and anxious, your veterinarian may need to give some sedation before further diagnostics can be done. Once your veterinarian notes the characteristic high heart rate, she will quickly pass a nasogastric tube. This is a long, pliable tube that is inserted through the horse's nose, and, once the horse swallows it, passes down the esophagus and into the stomach. This is a procedure that should only be done by a veterinarian, because it is surprisingly easy to pass the tube into the trachea (windpipe) rather than the esophagus, with potentially fatal consequences.
If your horse has proximal enteritis, there will often be a spontaneous rush of foul-smelling, red-brown fluid from the stomach. Occasionally, your veterinarian will have to prime the tube with a few pumps of water in order to help evacuate the stomach and small intestines. The fluid will often be enough to fill at least one water bucket (3 to 4 gallons). This procedure is both diagnostic and therapeutic.
Horses with surgical causes of colic may experience temporary relief after being refluxed, but the pain will return rapidly, their heart rates will remain high, and eventually will not respond to either sedatives or reflux. Horses with proximal enteritis, on the other hand, experience rapid and very visible relief after being refluxed. As long as their intestines and stomach are kept decompressed their heart rates will remain low and they will not be painful. Instead, they will look depressed and quiet.
Your veterinarian will perform a rectal examination to evaluate whether there are distended loops of small intestine. If the small intestine is not resorbing fluid, then the backed up fluid will eventually cause the small intestine to become taut and swollen with the fluid. It is often described as "feeling like party balloons." Although this finding will signify a serious intestinal problem, it will rarely suffice to let your veterinarian determine whether there is a medical or surgical problem.
Although the small intestine is rarely visible on ultrasonographic examination in normal horses, once it becomes distended with fluid, it is large enough and has sufficient contrast with the surrounding tissue to be seen. The small intestine will appear very quiet – the normal, continual motion that helps to propel the gut contents along is no longer working because of the intense inflammation. On the screen, this will look like multiple white circles filled with black fluid. However, as with rectal palpation, this ultrasound appearance may be seen with both medical and surgical causes of colic.
Abdominocentesis refers to removing a small amount of fluid from the space that surrounds the intestines. This space is called the peritoneum, and the fluid is called peritoneal fluid. In the normal horse, there is just a small amount of peritoneal fluid, which helps to lubricate the outsides of the intestines and helps to protect the peritoneal space from becoming infected.
Abdominocentesis can be performed with a needle or with a specialized instrument. It is a simple procedure but is mildly invasive. Normal peritoneal fluid is clear, and straw colored. It has a low protein count and a low number of white cells. In the prototypical case of proximal enteritis, the inflamed intestinal walls allow protein to infiltrate the peritoneal fluid, but the damage is rarely enough to let a high number of white cells seep into the peritoneal fluid. In the textbook surgical colic, the intestinal walls are more critically damaged, and both protein and white cells infiltrate the peritoneal fluid. In reality, either of these scenarios can be seen with either disease. It is a helpful test, but hardly definitive.
Although a CBC is rarely available on an emergency basis on the farm, it can usually be run at a referral hospital. Horses with very acute inflammation may have a low white cell count, because all the cells are going to the site of the problem to help fight off any possible infection. Later in the disease, the white cell count may be normal or elevated. Often, the CBC will include measurement of a protein called fibrinogen. An elevated fibrinogen level may indicate infection or inflammation.
A chemistry profile will allow your veterinarian to look for signs of dehydration that may lead to kidney problems, as well as any electrolyte abnormalities. Horses with proximal enteritis often have low chloride levels, and may have low sodium levels as well, because sodium and chloride are lost in the small intestinal fluid. This test must also either be done at a referral hospital, or the results must usually wait for the next day. Again, these are not specific findings.
A blood gas will allow your veterinarian to look for signs of acid base abnormalities that may arise because of fluid losses, dehydration, and poor blood circulation.
If your horse has proximal enteritis or a surgical cause of colic, your veterinarian will offer referral to an equine hospital where either surgery or intensive care can be done. Even with the best of diagnostics, it can be difficult to make the determination whether surgery is necessary. Proximal enteritis is extremely labor intensive, and it may require skilled, around-the-clock treatment for many days. It is very difficult to manage at the barn.
Exploratory surgery may be necessary for the horse that doesn't respond to medical treatment. Although our considerable increase in diagnostic techniques and abilities over the past few years has greatly improved our ability to accurately diagnose different causes of colic, the best determination as to whether a horse requires exploratory surgery is his response to gastrointestinal decompression and his response to anti-inflammatory, analgesic and sedative drugs. Horses that remain painful despite medical therapy are definitely candidates for surgery. Recent evidence suggests that horses with proximal enteritis do no worse after surgery and may indeed recover more quickly.