Signalment: 2 year old paint filly used for trail riding, kept in large wooded field with few other horses

History: 2 day history of lethargy and inappetance 

1. Port Wine Colored Urine

This is the most significant problem noted in the initial exam and lab results due to its indication that there is likely hematuria (blood in the urine.) Hematuria can indicate multiple different issues, including neoplasia, kidney disease and hemolytic anemia.¹ Urinalasys would be useful to conclude this. 

2. Low Hemoglobin

This is another significant issue uncovered in the initial blood results. Since hemoglobin is a transporter of oxygen, low hemoglobin can negatively impact overall oxygenation of tissues and if prolonged and severe enough, can lead to shock and in severe cases death.²

3. Depressed Mentation

It was noted during the history and physical exam that the horse had a depressed mentation. While this could indicate a multitude of medical conditions, the reason depressed mentation has been included as a critical problem is that when coupled with an increased heart rate (100 bpm, compared to the reference range of 24 to 44 bpm) it can be inferred that the horse is experiencing a significant amount of pain.¹¹ Additionally, with the note that this behavior began within the past day or two, it can be assessed that this is not a chronic problem, indicating that there is a malicious pathology going on. 

1. Red Maple Leaf Toxicosis

This is clearly the first and most easily supported differential. Red maple leaf toxicosis is characterized most often by weakness, lethargy, muddy or cyanotic mucous membranes, tachycardia and pigmenturia, all of which are being exhibited by this filly and were easily detectable on the physical exam and by grossly viewing a urine sample.³ It was noted that the pasture the filly is kept in was heavily wooded, so it is not unreasonable that she could have been exposed to wilted maple leaves and eaten them. It was also noted that she was not kept with many other horses so it is not shocking that no other horses were reported ill.

The toxicity caused by red maple leaves causes hemolysis (breaking up) of red blood cells, and throughout her bloodwork we see indications of hemolysis. These include a high mean corpuscular hemoglobin concentration, high total protein and albumin, low hemoglobin and low hematocrit.

Hemoglobin concentration indicates the amount of oxygen carrying molecules in the red blood cells.⁴ Hematocrit is the the percentage of red blood cells within total blood volume, was also low.  Mean corpuscular hemoglobin concentration, the amount of hemoglobin in each red blood cell was low. When the RBC smear was observed, hemolysis and ghost cells were seen. Total protein and albumin were high, also indicating hemolysis.⁵ 

2. Colangiohepatits 

This is an inflammation of the liver and bile system. The cause is not always clear and clinical signs can be varied. However, fever, depressed mentation, lethargy, and elevated gamma glutamyl transpeptidase (GGT) are commonly associated with this pathology, all of these were noted to be exhibited by this filly.⁶ 

The one issue associated with this differential is that it does not account for the dark urine, a key problem identified in the initial examination. 

An ultrasound of the bile ducts and liver is needed to conclude or eliminate this differential. A positive indication of colangiohepatitis would include dilated bile ducts and potential hyperechoic calculi. If this is inconclusive, a liver biopsy is needed to attempt to identify neutrophillic colangiohepatitis and potential fibrosis.⁶ 

PCO₂ Results:

PCO₂ is a reflection of ventilation. This filly's PCO₂ was low, potentially indicating hyperventilation, or increased ventilation relative to metabolic demands.⁷ This can be a result of pain or hypoxemia. Since the horse had a high heart rate and was reported to be depressed, it is very likely that she was in pain.¹¹ Also, since there is some level of hemoglobin damage going on, it is possible she is also hypoxemic. This would likely be reflected in cyanotic membranes and fatigue⁵, which this filly has.

Hematocrit Findings

Hematocrit is the percentage of red blood cells to the total blood volume, it was found to be quite low, indicating potential anemia. This is not unexpected since the filly's mucous membranes were noted as muddy and cyanotic. Anemia often also causes lethargy and tachycardia, which were both noted in her history.⁹

Blood Gas

A blood gas was likely performed in response to the muddy cyanotic membranes and the dark red urine. The cyanotic membranes could indicate low red blood cell or hemoglobin levels¹² and the dark red urine could potentially mean there is blood loss through the urine.¹ It could be expected that the blood gas may reveal some level of hypoxemia and potentially hypoxia due to blood loss. This was indicated in the low hematocrit, low hemoglobin and low pCO₂.⁵

Other Diagnositc Tests:

As noted in the problems section, a urinalysis would be useful to identify the reason for the dark urine, though upon visual examination we can assume it is blood.

Also, as mentioned in the differential section, an abdominal ultrasound reflected an increased echogenicity of the liver and dialated bile ducts and liver biopsy could prove useful to rule in or out colangiohepatitis. ⁶ 

Clinical Signs

If unmanaged, we can expect her to become increasingly lethargic and depressed and she could eventually become obtunded. She may also exhibit signs of colic and develop laminitis.³ In severe cases there is a potential for her to develop more severe neurologic signs like head pressing.⁶

Management

In the case of red maple toxicosis causing hemolytic anemia, the mainstay of treatment is supportive care, pain control and steroids to decrease the activity of the immune system. This can include administration of crystalloids, intravenous NSAIDs to reduce inflammation, blood transfusions to replenish the lost red blood cells, administration of ascorbic acid (viramin C) that is aids in making new red blood cells, and corticosteroids that function as an immunosuppressent and anti-inflammatory.³

If colangiohepatitis is concluded after further testing, antibiotics and fluid administration would be a solid treatment option. This treatment would be continued until GGT ( Gamma-Glutamyl Transferase, a liver enzyme elevated when the liver is compromised) comes back down into normal range.⁶

Associated Scientific Concepts

It is important to understand what hemolytic anemia is to understand this case since there are multiple clinical signs and evidence in bloodwork that indicates this. Hemolytic anemia is often mediated by the immune system. It can be autoimmune or induced by toxins like the red maple leaf. It causes the body to lyse the red blood cells, resulting in the low hematocrit and PCV seen in blood work as well as the bloody urine⁴.

Another important concept is that of the equine biliary system, since colangiohepatitis (inflammation of bile duct and liver) is a key differential in this case. Horses have no gallbladder to store bile so bile formed in the liver flows straignt into the small intestine through a non-functional sphincter of oddi.¹⁰

One key issue I ran into while examining this case was my difficulty in understanding blood gasses. I found that a lot of material felt familiar and I knew a lot of technical definitions of words used for this from classes, but I had little knowledge about how to implement this information into an actual case and what the implications of these things being out of reference ranges would be. In order to combat this issue, I researched a lot of example cases to get an idea of how to do this. 

Another issue I identified was that I felt I did not have enough evidence to focus on either one of my differentials. I felt like I could have chosen a few different ones to focus on with the information provided, it seemed very open ended. It would have been more helpful to be able to request a more complete history (e.g. how often is she monitored, history of health issues, are there other horses sick too, etc.) and what kidney and liver values were.