Proximal Enteritis (Proximal Duodenitis/Jejunitis, Anterior Enteritis)

Proximal enteritis is an inflammation of the first section of the small intestine and is a very serious cause of colic, or abdominal pain, in the horse. No one really knows what causes proximal enteritis. Some veterinarians suspect that there is a bacterial cause, but no single definitive cause has been defined.

Some veterinarians report geographic areas where proximal enteritis is more common. It may have to do with the types of bacteria that naturally occur in certain locations. More cases seem to be seen in the southeastern United States.

Older horses are more susceptible to proximal enteritis, but it is also seen in young horses one to two years of age.

The inflammation causes the affected part of the intestine to malfunction. The intestine ceases to absorb fluids, and instead, large amounts of fluid accumulate in the intestine. The fluid accumulation causes the horse to become extremely dehydrated. Although he is undergoing continual water loss, it is futile for him to drink, because he can't absorb the fluid.

Because horses are unable to vomit, the fluid causes the intestines, and eventually the stomach, to swell and become extremely painful. Eventually, if this fluid build-up is not relieved, the stomach or intestines may rupture.

Proximal enteritis is easily mistaken for a surgical cause of colic, such as twisted small intestine. Even with the best of diagnostic equipment and skills, your veterinarian may not be sure whether your horse requires colic surgery. The signs of colic, reflux, and distended small intestine may go with either problem.

Although there are some differences in some cases of proximal enteritis, such as fever, slightly less pain than with a surgical colic, and far more reduction of pain after reflux, not all cases follow the book.

What to Watch For

• Loss of appetite
• Signs of abdominal pain (paw, roll, get up and down repeatedly)
• Abrasions over the eyes or on bony areas of the body
• Dry tacky gums
• Depression
• Fever
• Lack of manure production
• Lack of thirst
• Increased respiratory rate
• Bloated appearance
• Lameness, warm feet

Diagnosis

The most important diagnostic goal for your veterinarian is to determine if your horse can be treated medically or if the horse requires surgery. If your horse needs medical therapy, then your veterinarian will have to determine if therapy can be administered at home or if referral to an equine hospital is necessary.

• Your veterinarian will perform a rapid but thorough physical examination, especially noting heart rate, respiratory rate, rectal temperature, and the presence of gut sounds.
• Your veterinarian will reflux your horse, which is the use of a nasogastric tube to relieve distention of the small intestine. Horses with proximal enteritis, as opposed to a surgical cause of colic, will experience pain relief as long as the intestines and stomach are kept decompressed.
• An rectal examination will determine if there are distended loops of small intestine.
• Examination of the abdomen with ultrasound will detect small intestinal distention.
• Abdominocentesis (belly tap) will detect signs of inflammation.
• A compete blood count (CBC) may detect signs of infection or inflammation. This test is usually not available on an emergency basis to your veterinarian; results are usually not available until the next day.
• A chemistry profile will look for signs of dehydration, electrolyte imbalances, and possible kidney problems secondary to dehydration. This test is usually not available on an emergency basis as results are usually not available until the next day.
• A blood gas will help assess acid-base abnormalities.
• Because it is can be very difficult, and sometimes impossible, to differentiate proximal enteritis from a surgical cause of colic, such as twisted small intestine, your practitioner will usually recommend referral to a facility that performs colic surgery. In some cases, an exploratory surgery is necessary to determine the cause of abdominal pain and reflux in your horse.

Treatment

Proximal enteritis can be a very expensive disease, due to the high cost of intravenous fluids and nutritional support.

• The most important, life-saving treatment is gastric and small intestinal decompression. This is done using an indwelling nasogastric tube and will have to be repeated frequently throughout the day and night.
• Intravenous fluid therapy is imperative in countering dehydration.
• Electrolyte imbalances can also be addressed with fluid therapy.
• Antibiotics may or may not be given, depending on the individual case.
• Anti-inflammatory drugs, especially Banamine, will help to make the horses more comfortable, and may counter inflammation.
• If your horse develops laminitis, your veterinarian will pursue specific treatment for that problem. It is important to make sure that your horse is bedded comfortably in deep shavings, peat moss or sand.
• Some veterinarians choose to treat with DMSO, heparin, pentoxyfylline, and acepromazine to counteract the effects of inflammation. Proximal enteritis usually requires many days of critical care treatment, and often requires hospitalization.
• Horses with proximal enteritis may need intravenous nutritional support if the period of reflux lasts more than a few days.

Proximal enteritis refers to an inflammation of the duodenum and jejunum, which are the first segments of the horse's small intestine. It is a serious cause of severe abdominal pain, or colic and usually has a very acute onset – the horse is typically described as having been completely normal within the past 24 hours.

The cause of proximal enteritis is unknown. Certainly many clinicians suspect that there is a bacterial cause of proximal enteritis.

Proximal enteritis seems to have different levels of severity in various areas of the country, with the most severe cases being seen in the southeast of the United States. Certainly, each locale has its own resident population of normal bacteria, and it may be that for unknown reasons, these normal bacteria can become pathogenic under certain circumstances.

Although proximal enteritis is seen in all ages, it certainly seems to be more common in older horses.

In the normal horse, the contents of the intestines are continually propelled away from the mouth and toward the anus by peristalsis – a wave of worm-like contractions passing along the entire digestive system. In the normal condition, the small intestine also resorbs large amounts of fluid on a daily basis, both fluid that the horse drinks, and fluid that normally enters the intestines from the rest of the body. With proximal enteritis, whether the cause is bacterial or not, the ensuing inflammation causes damage to the intestinal walls. This causes the intestines to stop their peristaltic action – termed ileus – and to stop resorbing fluid. This in turn causes the horse to become extremely dehydrated, and causes the intestines to become severely distended. The distension causes the horse to experience abdominal pain that can be extremely severe, and thus results in signs of colic.

Because the walls of the intestines have become compromised, bacterial toxins, especially one called endotoxin, can seep into the body. Endotoxin can cause fever, high heart rate and pain.

The most important differential diagnosis for proximal enteritis is any other cause of small intestinal damage that requires surgical intervention. This may include a twisted or entrapped small intestine. Both proximal enteritis and surgical problems cause signs of colic, voluminous backed-up fluid in the stomach and small intestine, and distended small intestine on examination per rectum. However, small intestinal twists or entrapments usually cause the affected portion of the small intestine to die, thus requiring surgery, whereas the damage caused by proximal enteritis can usually be repaired by the body as long as supportive therapy is provided.

The horse with proximal enteritis has a good prognosis; however, this is usually a very expensive disease to treat.

• 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.
• The most important initial treatment is to get a nasogastric tube into the horse quickly. It is possible for the stomach to burst if the fluid load is not relieved, and distension of the stomach and intestine can cause excruciating pain. Distention of the intestines themselves can contribute to intestinal dysfunction, so good and consistent decompression leads to a more rapid recovery. It is usually necessary for the horse with proximal enteritis to have a nasogastric tube left in place, because these horses must often be refluxed every two to four hours due to the rapid build-up of fluid.
• Your horse will usually have an intravenous catheter place in one of his jugular veins, and will receive fluid through this catheter. Horses with proximal enteritis often require as much as 60 to 100 liters of fluid per day (approximately 30 to 50 gallons), which is one of the reasons that this disease is so labor-intensive and expensive.
• Although no specific bacteria have been identified as a cause of proximal enteritis, many veterinarians choose to give broad-spectrum antibiotics. It seems that antibiotics are more useful in some areas of the country than others, confirming the clinical suspicion that there are many different causes for proximal enteritis, and the level of severity differs according to the cause.
• Anti-inflammatory drugs, especially Banamine, can help to relieve your horse's pain and inflammation. However, Banamine can potentiate kidney disease, especially if your horse is dehydrated, so it is important to monitor the horse's kidney function and level of hydration.
• Any systemic disease or inflammation can cause horses to develop laminitis, or founder. Laminitis is a particularly dreaded sequel to proximal enteritis, as it can sometimes be harder, and more frustrating, to treat than the original disease. There are few good ways to prevent laminitis, but deep, soft bedding may be helpful, as is good hoof care. Many clinicians now choose to ice the horse's feet in the initial stages of disease, in order to keep inflammatory mediators from reaching the hoof.
• There are many ancillary treatments, such as DMSO to decrease inflammation, pentoxyfylline to counter the toxins associated with proximal enteritis, and acepromazine to possibly improve circulation in the foot. None of them has been proved effective, but they may be of some help.
• If the horse with proximal enteritis is not able to eat for longer than 3 to 5 days, it may be necessary to pursue parenteral nutrition, or nutrition that is given through a catheter in the vein. This can be extremely expensive, but can also be very valuable in maintaining the horse's strength.

Home Care

• Your veterinarian will recommend that you keep your horse from hurting himself while waiting for veterinary help, but it is not necessary to keep your horse walking. However, many horses seem to experience some sort of relief from walking.
• Your veterinarian will usually prefer that you not give your horse any drugs such as Banamine or sedatives before her arrival. These drugs can mask signs that are important clues for your veterinarian in diagnosing this disease.
• You should not feed your horse anything while you are waiting for the veterinarian to arrive.
• Once your horse is home, your veterinarian will usually advise that you feed a bland diet of frequent small meals for many weeks. It is important that your horse does not experience any sort of dietary overload.

Preventative Care

• The best way to prevent proximal enteritis is to practice good management. In general, horses should be fed frequent, high fiber, small meals to avoid nutritional overload. Most horses receive too much grain in relationship to the amount of hay they are fed.
• Make sure that your horse always has plenty of fresh water.
• Strive for as much turnout as possible. Ideally, horses should live outside 24 hours a day, as long as they have a three-sided shed or appropriately located trees to act as a shelter from wind and rain.