Case Reports

PSSM Case Report

Courage is an eleven year old 16.3 hand Thoroughbred gelding, purchased as a seven year old with the hopes of him becoming an event horse and fox hunter. Courage proved to be a poor-keeper as he failed to develop adequate muscle in his top-line, neck, and hindquarters despite an appropriate feeding program, good dental care, and a consistent exercise regimen. His diet consisted of 10 lbs. of grain per day (a commercial 12% protein and 8% fat concentrate), probiotic weight supplements (Hard Keeper and Focus Wt), ample grass hay, and 12 hours of daily turn-out. While under saddle, he demonstrated great difficulty remaining on-the-bit and balanced on 20 meter canter circles. Courage would become "grouchy" and occasionally nip while being groomed. He was also very difficult to shoe as he was reluctant to hold up either hind leg for any extended period of time.

In January of 2004, the owner noticed progressive muscle soreness during the formal fox hunting season. He presented to MEVA for evaluation of severe hind limb stiffness several days following a strenuous 3 hour fox hunt. A thorough exam revealed severe muscle pain and an abnormal bilateral hind limb gait. The hind limb gait could be characterized as exaggerated hock flexion, followed by a shortened anterior phase of the stride, and then an abrupt "slapping" of each hind hoof back onto the ground. This abnormal hind limb gait was most exaggerated during the transition from the halt to a walk and the gait seemed to improve slightly as he continued to walk. His muscle pain was evident with even light digital palpation and was localized to the lumbar muscles, gluteal muscles, and the sacro-iliac region. Hind limb flexion tests were negative. A neurologic exam was also performed and no abnormalities were noted. Severe musculoskeletal pain secondary to trauma and exertional rhabdomyolysis (tying-up) were thought to be likely diagnoses. Due to Courage’s long history of poor muscle development and stiffness, Equine Polysaccharide Storage Myopathy (EPSSM) was also placed on the differential diagnoses list.

Initial treatment included stall rest with turn-out, a series of acupuncture treatments (dry needle and electro-acupuncture), Chinese herbal therapy (Qi Performance: Body Sore), and vitamin E supplementation (6,000 IU vitamin E/day). His diet was gradually changed from a high carbohydrate diet to a low-carbohydrate high-fat diet (Ultium feed made by Purina). In addition, one cup of vegetable oil was added to his feed twice daily to increase his fat intake. A skeletal muscle biopsy was performed at the MEVA clinic and shipped to Oregon State University for histopathological analysis. The muscle biopsy revealed moderate to severe glycogen storage within the skeletal muscle fibers consistent with EPSSM.

Courage responded very well to treatment. His muscle soreness and abnormal hind limb gait resolved quickly. Several days following his first acupuncture treatment and diet change, Courage stood well for the farrier. Over the past year, he has progressively gained weight and developed more muscle in his neck and hindquarters. His performance under saddle has improved and he is now cantering 20 meter circles without difficulty. Courage is currently maintained on approximately 3.5 pounds of Ultium top-dressed with 1 cup of vegetable oil twice daily and 24 hour turn-out. He is starting back into consistent work under-saddle.

Foal Case Report

This foal was born weak & unable to nurse well (hypoxic & septic). After 3 days of intensive care the foal was able to stand unassisted. On day 7 the foal went home.

This is the foal on the farm just before weaning.

Equine Polysaccaride Storage Myopathy (PSSM)

Equine Polysaccharide Storage Myopathy (EPSSM) is a muscle disorder characterized by increased accumulation of glycogen and the presence of abnormal polysaccharide complexes in skeletal muscle. The excessive accumulation of glycogen within the skeletal muscle tissue has been found to be a result of increased insulin sensitivity in some affected breeds. This increased insulin sensitivity results in rapid clearance of glucose from the bloodstream following a carbohydrate meal followed by deposition of the glucose in the form of glycogen within muscle tissue. The defect leading to the accumulation of abnormal polysaccharide has yet to be reported.

Several years ago, EPSSM was thought to only affect Quarter Horses, Paints, and draft horses such as, Percherons and Belgians. However, the condition has now been diagnosed in many breeds including Thoroughbreds, Arabians, Morgans, Friesians, Appaloosas, and American Saddlebreds.

Clinical signs observed in horses with EPSSM include muscle weakness, loss of muscle mass (muscle atrophy), exercise intolerance, difficulty holding up limbs for the farrier, sensitivity to grooming, and recurrent episodes of exertional rhabdomyolysis (tying-up). The severity of clinical signs can vary greatly. In mild cases, horses may tire easily during exercise. Varying degrees of decreased muscle mass and/or mild muscle stiffness may be evident. In horses with severe episodes of exertional rhabdomyolysis or tying-up, generalized muscle stiffness and cramping with reluctance to move may occur during or immediately following exercise. Severe weakness and periods of recumbency (the inability to rise) are the most common signs observed in draught horses with EPSSM.

Diagnosis of EPSSM is based on histopatholgical characteristics of muscle biopsies. Performing a muscle biopsy is a relatively easy procedure that can be performed in a standing sedated horse. In some cases, blood work may demonstrate elevations in muscle enzymes. Management of horses with EPSSM is based on decreasing carbohydrate ingestion and feeding a high fat diet combined with regular exercise. As with all horses, total forage should be fed at a rate of 1.5-2% of body weight per day. In the average 1000 pound horse, this means 15 to 20 pounds of dry matter intake per day. In horses with EPSSM less than 10% of the diet should be composed of carbohydrate or starch. The amount of fat necessary in these horses’ diet is controversial. In mild cases, low-starch diets with light supplementation with fat may be sufficient. Fat supplementation may be achieved with the addition of vegetable oil such as corn, soy, peanut, coconut, safflower, linseed, flaxseed, and canola. Unfortunately some horses find oil supplementation unpalatable. Alternatively, rice bran which contains about 20% fat can be added to the diet. In severe cases of EPSSM diets composed of up to 20-25% fat may be necessary to achieve resolution of clinical signs. Currently there are several commercial low carbohydrate high fat feeds available. In addition to diet, consistent exercise under saddle and/or ample turn-out is very beneficial especially in EPSSM horses that show signs of exertional rhabdomyolysis (tying-up).

Foals

The foaling season for MEVA clients this past spring was very busy. We treated foals with conditions such as birth hypoxia (oxygen deprivation), sepsis, diarrhea and pneumonia. Hospitalized foals required intensive care treatments including continuous IV fluids, stomach tube feeding, and oxygen therapy.

Foal care is very intensive because they require constant monitoring. Starting in January 2006, we will be acquiring a staff of volunteers to assist with our foaling season. Foal team duties will include holding mares, assisting technicians with treatments, foal monitoring, lifting, etc. Contact our technician, Sarah Allgood, if you are interested in volunteering some time. Please note that volunteers must be 16 years of age or older.