Allergic Airway Disease in horses.

In the past 30 days (July 8 - August 8) I have examined 10 horses for the complaint of coughing and poor performance. The horses have ranged in age from 8 to 19 years of age. There has been no commonality with regards to sex or breed. However, they all live in Florida and it is the hottest month of the year!  Through a series of diagnostics which include a re-breathing exam, upper airway endoscopy, and trans-tracheal wash, all 10 horses have been diagnosed with allergic airway disease (AKA: heaves or COPD). None of these horses had previously been diagnosed with this condition. 
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Upper trachea with large amounts of sputum present.

Lower trachea with thickened mucosa due to chronic inflammation

Allergic airway disease in horses typically results in coughing, increased respiratory effort, increased "abdominal" breathing, exercise intolerance and weight loss. If not managed properly, the condition worsens from year to year and can result in the death of the horse!! I have posted a blog previously discussing this disease and how it should be diagnosed and treated. Please click on the link below to read my blog from last year regarding this condition.

Allergic Airway Disease in a Horse

Collapsing Trachea in a Miniature Horse

A three year-old miniature stallion presented to PHD Veterinary Services for the complaint of open mouth breathing and a "honking" sound during respiration. At presentation, the stallion was agitated and was continuously pawing at his muzzle with his mouth open. The stallion was mildly sedated for the endoscopic exam and interestingly, his breathing became more normal. The most proximal trachea (Figure 1) appeared normal in diameter however the lumen quickly became narrowed (Figure 2). The trachea was nearly completely collapsed for approximately 6 cm at the level of the thoracic inlet. Distal to this area, the trachea appeared normal (Figure 3).

Figure 1

Figure 2

Figure 3

Normally, the lumen of the trachea is continuous, extending from the larynx to the primary bifurcation of the trachea (Figure 4). Unfortunately, the miniature horse breed is predisposed to the condition known as collapsing trachea. The condition is often diagnosed shortly after birth or can develop later in life if the horse is allowed to gain excessive weight. A common clinical complaint is that of a "honking" sound during heavy respiration. The severity of the collapsing trachea depends on the location and the extent of the narrowed lumen. The closer the area of collapse is to the chest cavity, the worse the prognosis. There are reported cases of collapsing tracheas in miniature horses that were repaired via intra- and extra-luminal stents. Unfortunately, they are short term fixes and often do not provide a long term solution.

Figure 4

Ethmoid Hematoma versus Paranasal Sinus Cyst in a Horse

Two horses presented to PHD Veterinary services for the same complaint of "no air moving through one of the horse's nasal passages!" Both horses had a history of mild to moderate nasal discharge that had increased slowly over the past 6 months. On presentation, a simple evaluation of air passing through the nasal cavities revealed that there was NO air moving through the affected side on each horse however, endoscopic exam revealed a unique problem in each horse.

Figure 1

 In Figure 1, a smooth, white soft tissue mass was identified within 2 inches of the opening of the nasal cavity. This soft tissue mass was completely obstructing the nasal passage. In addition, when the scope was passed through the unaffected side, the soft tissue mass was noted to be extending into the naso-pharynx suggesting that the soft tissue mass extended through out the entire nasal passage (Figure 2). In Figure 2, the white wall of tissue noted along the right side of the image is the soft tissue mass as it extends into the naso-pharynx.The soft tissue mass is most likely consistent with a paranasal sinus cyst however surgical removal will be required to confirm the diagnosis. These types of cysts develop in young horses and grow slowly over months and years until a clinical problem develops. Surgical removal provides complete resolution of these types of cysts!!

Figure 2

Figure 3

In the second horse, a large golden-colored soft tissue mass was identified in the region of the nasal passage closest to the naso-pharynx. There was more discharge associated with this soft tissue mass and small areas of hemorrhage were noted. The soft tissue mass was completely obstructing the nasal passage and was originating from the ethmoid turbinate region which most likely classified it as a ethmoid hematoma!! These types of tumors typically present with a complaint of a unilateral bloody nasal discharge for months before they completely obstruct the nasal passage. However, they can be fast growing tumors and require an aggressive approach to eradicate. Treatment may involve either surgical removal or repeated injections of formalin. It has been my experience, having injected several horses for YEARS, that the tumors tend to return with this approach! Hence, I recommend surgical removal when first diagnosed, especially if the tumor is invading the sinus cavity or the naso-pharynx.

Severe Roaring in a Horse!!

A teen-age mare presented for respiratory noise during exercise and poor performance. The mare had made noise during exercise for the past 2-3 years WITHOUT poor performance. Interestingly, the mare has always been resistant when cantering to the RIGHT! Recently, it was noted that the mare demonstrated signs of exercise intolerance at the canter. During the exam, the mare was asked to canter on a lunge line and she carried her head to the outside of the circle with her nose turned up. After 1-2 minutes of cantering to the right, it became increasingly more difficult for her to catch her breath and she would occasionally cough/gag violently!. 

Figure 1

 The mare was scoped immediately after exercise and complete paralysis of the left arytenoid was discovered (Figures 1-2). During inspiration, the left arytenoid was across mid-line (yellow line) and obstructing at least 50% of the mare's airway (Figure 2).  It is highly likely that during heavy exercise, the increased negative pressure during inspiration would cause the paralyzed arytenoid to completely cover the airway and prevent the mare from breathing! 

Figure 2

In addition, while scoping the horse, the mare tended to displace her soft palate in such a position that the epiglottis was trapped below (Figures 3-4). When this occurred, the mare instantly began to cough/gag until she corrected the displacement! Displacement of the soft palate is not always associated with arytenoid hemipligia but when it does occur may worsen the exercise intolerance.

Figure 3

The prognosis for this mare is dependent on additional evaluation by an equine surgeon and the recommended surgical procedure. If she is a good candidate for surgery and the surgery is a success, there is a good likelihood that she will return to work and perform significantly better than before.

Chronic Obstructive Airway Disease in a Horse

The endoscopic image in Figure 1 is from within a horse's trachea. In Figure 1, the endoscope is positioned just in front of the main bifurcation of the trachea where it splits into the right and left bronchi (Figure 2) . This is just in front of the horse's heart also known as the carina! The purpose of passing an endoscope down to this level of the horse's respiratory tract is to evaluate for the accumulation of debris (feed material, pus and/or blood) and to perform a diagnostic procedure called a bronchoalveolar lavage (BAL). In this particular case, the horse presented for a chronic cough and exercise intolerance.

Figure 1

Figure 2

As the endoscope was passed down the trachea there was a moderate amount of white foamy fluid along the ventral aspect of the trachea (Figure 2 and 3). This debris is consistent with sputum that originates within the lung tissue and is coughed into the trachea. This finding can be consistent with either pneumonia (bacterial infection) or an allergic airway condition that is also known as COPD/Heaves! To determine the cause of the sputum, a BAL is performed. In this procedure, the endoscope is passed into the primary bronchi until it is lodged within the bronchi. At this point a small volume of sterile saline is passed into the bronchi through the scope and then collected via aspiration. The fluid is analyzed to determine the percentage of different cell types and from this data, it can be determined if the horse has an infection or allergic airway disease.

Figure 2

Figure 3

The importance of determining which disease process is causing the sputum is that treatment for allergic airway disease involves systemic corticosteroid administration which will lower the horse's immune system and significantly worsen any bacterial infection the horse may have!! Hence, it is key to perform the BAL  prior to any treatment to determine if the horse needs antibiotics or steroids or maybe antibiotics plus steroids!! The BAL can be performed stall-side with a sedated horse.

Equine Pharyngitis!!

The image above was from a 10 year old gelding that presented for a history of coughing and mild nasal discharge. The cough was intermittent and would vary from day to day. Recently, the cough had worsened as had the summer heat! Based on the history, the most likely cause was predicted to be heaves (AKA: COPD). However, when the endoscope was introduced into the gelding's upper airway it was clear that we were dealing with something quite different. There was evidence of pharyngeal scarring (cicatrix) and active pharyngeal ulceration  in a 360 degree (red circle below) range.  These findings were consistent with active inflammation and chronic changes. In addition, there was chronic, active inflammation of the arytenoids (green arrow).

The cause of pharyngeal inflammation/ulceration varies and is often never determined. In some cases, it may be complicated by bacterial infection. In some cases, the inciting cause is presumed to be an environmental irritant that the horse is chronically exposed to. The chronic inflammation results in scarring or cicatrix formation that can result in narrowing of the pharynx. Pharyngeal cicatrix formation is a serious complication that has no reliable remedy!  As such, a chronic couch (>2 weeks) should be evaluated via endoscopy prior to the development of scarring. Pharyngeal inflammation is typically treated with forced rest and topical antibiotics/steroids in the form of a nasal flush.