Laminitis and Metabolic Syndrome
While veterinary investigators from around the world improve our understanding of the causes of laminitis and its effective management, the disease remains one of the most debilitating for horses as well as the most frustrating for clients, attending veterinarians and farriers alike. In a USDA study (pdf) specifically looking at laminitis in the U.S. horse population, 46% of owners perceived that their horses became laminitis because of introduction to lush pasture. Another 27% felt that the laminitis was secondary to feed problems, obesity pregnancy or injury. Less-common causes included diarrhea, grain overload and retained placenta.
The most common theme is thus related to feed management and body condition of the animals involved.
The following two cases, presented to Tufts’ Hospital for Large Animals, represent one of the underlying conditions we see that predispose horses to laminitis, Equine Metabolic Syndrome. They also illustrate the strategies we use and the principles we follow to optimize long-term outcome.
A 14 year-old Dutch Warmblood gelding presented for the evaluation of bilateral (both-sided) forelimb laminitis, first diagnosed by the attending veterinarian 2 months earlier. At the time of onset, the horse was treated with flunixin, acepromazine, DMSO and icing of the feet, which brought an improvement in soundness. However, a significant worsening of lameness ensued 5 days prior to presentation at Tufts. The referring veterinarian’s radiographs confirmed coffin bone rotation relative to the anterior hoof walls of both front feet.
Upon presentation to Tufts, the horse had normal vital parameters (temperature, heart and respiratory rate, digital pulses). He was wearing egg-bar shoes and flat pads, each shoe possessing 4 studs to aid traction during the winter season. At the trot, a shortened stride in both forelimbs with a consistent 2/5 lameness (0 = not lame, 5 = non-weight bearing lameness) in the left fore was noted. The horse was not sensitive to hoof testers. He had a body condition score of 6 (moderately fleshy) and a firm, crested neck.
Plain radiographs and venograms of both front feet were completed. The plain radiographs confirmed 7º (right) and 8.5º (left) rotation of the coffin bone relative to the (anterior) hoof wall, as seen in the picture above.
Both hooves had relatively long toes and moderately thin soles for the size of horse. Venograms (contrast injected into blood vessels of the feet) revealed generally good perfusion of the entire digital vasculature. The circumflex vessels of both hooves were mildly displaced and a small volume of dye had leaked from the vessels at the dorso-distal extent of the left coffin bone (Image 2; a), both signs consistent with mild damage.
Fasting blood work performed prior to admission revealed elevated insulin (102 µU/mL; normal 5-20) and normal glucose (94 mg/dL; normal 60-125), indicative of insulin resistance. Based on the horse’s clinical findings and his moderately fleshy body condition score, long-standing forelimb laminitis and associated equine metabolic syndrome were provisionally diagnosed.
Initial management was directed at mechanically optimizing the orientation and shape of both fore-feet to minimize further rotation, maximize blood supply to all hoof structures and promote sole growth. The toes of both forefeet were shortened by ~1.0-cm and wide-web 3º-wedge aluminum shoes (Trac-me®) with a rolled toe were applied in conjunction with polymeric putty supporting the frog and caudal (back) ⅔ of the sole under synthetic pads.
The horse was kept at the hospital for 24 hours post-shoeing to assess his response. Immediately prior to discharge his left forelimb lameness was undetectable although he retained a mildly shorter than normal gait in both front feet. At least 4 weeks of stall rest and hand walking or small enclosure turn-out were advised to be followed by reassessment.
To address the metabolic syndrome, the amount of hay fed was reduced by half with instructions to feed it in small quantities throughout the day. Because the amount of non-structural carbohydrates in the hay was unknown, the owners were instructed to soak the hay in cold water for 30 minutes and drain for 15 minutes prior to being fed. Hopefully this would decrease the amount of carbohydrates in the hay to a level that would not raise the horse’s insulin.
An 8 year old Oldenburg gelding was presented to the HLA with bilateral forelimb lameness first noted 5 days earlier. Radiographs taken at the time by the horse’s attending veterinarian revealed 7º of rotation separating the hoof wall from the border of the coffin bone. Laminitis was diagnosed. The horse’s soundness deteriorated in spite of therapy which had included flunixin, phenylbutazone, acepromazine, butorphanol and application of padded boots on both front feet.
On arrival at Tufts the horse was extremely reluctant to move. The front limb gait was short and very hesitant while both hind limbs exhibited a high-stepping gait. Heart rate and respiration rate were both increased at 60 per minute due to pain. While digital pulses were only mildly elevated, a moderate groove was identified along the coronary band of both front limbs, indicating potential sinking of the coffin bone. Body condition score was 8 (overweight).
Blood results revealed a normal ACTH (no evidence of early Cushing’s disease – PPID), mildly elevated insulin (34 µU/mL; normal 5-20) and high normal glucose (126 mg/dL; normal 60-125), potentially suggestive of underlying equine metabolic syndrome (EMS). Plain radiographs of all 4 feet and venograms of both front feet were performed. The plain radiographs confirmed 8-9º rotation and moderate sinking in both fore-feet as well as 5º rotation in the left hind foot. Toe length was relatively long in all 4 feet and the sole thickness in both front hooves was substantially reduced:
Venograms showed reduced blood supply to the upper (proximal) aspect of the dorsal laminae of both front hoof walls (Image 4; b), that was improved in non-weight-bearing views. The lower (disto-dorsal) aspect of the forelimb coffin bones was displaced below the circumflex vessels (Image 4; c) which in turn showed leak of contrast from the blood stream, consistent with tissue damage.
Acute laminitis with coffin bone rotation and sinking affecting both forelimbs as well as mild rotation of the left hindlimb was diagnosed. Equine metabolic syndrome was suspected as a predisposing cause. All 4 feet were placed in hoof-wear that provided ~10º heel elevation. The soles were packed with polymeric putty over their caudal ⅔ as was the frog to better distribute weight-bearing forces. The anterior hoof wall of both fore limbs was grooved down to the level of non-pigmented horn approximately 1-cm below the coronary band (Image 5; d). Dietary changes mimicked those implemented in Case 1 above. Medical management included phenylbutazone, acepromazine and ranitidine.
In response to treatment the clinical lameness improved in 24 hours from severe to moderate (Obel grade IV to III) and resting heart rate was reduced from 60 to 40 per minute. A steady improvement in soundness continued over the next week, while the horse continued to lay down for prolonged periods of each day. On day 18 after presentation, the coronary band of both forelimbs demonstrated a palpable groove extending from the toe to now include the inner (medial) and outer (lateral) quarters. Forelimb venograms were repeated, revealing a substantial worsening of blood flow in both fore-feet. Therefore, forelimb deep digital flexor tenotomies (surgical tendon transection) were performed at the mid-cannon bone level of both forelimbs. Derotation of the coffin bones was achieved by application of rail shoes and polymeric putty to support the caudal ⅔ (back) of the sole and frog [see below]:
The horse was subsequently discharged to a rehabilitation facility for several months of moderately intensive long-term care management.
For a complete discussion of these cases, including an in-depth analysis of Equine Metabolic Syndrome, please read this month’s Topics of Discussion.