Laminitis

• Horses don’t stand on their sole, they ‘hang’ from inside of the hoof wall by the intricate interdigitated tissues from inside of the hoof and outside of P3 (laminae). The hoof wall is the weight-bearing structure
• • Laminitis is inflammation of the laminae of the foot called ‘founder’
  • Founder should be reserved for when all of the laminae have failed and the pedal bone sinks, this is different to rotational laminitis (half the laminae fail e.g., just the medial aspect)
• Dermal lamellae (P3) and epidermal lamellae (hoof) are strongly bonded, to allow hoof growth this bond is released slightly via the action of matrix metalloproteinase (MMP). This is a carefully controlled process, you do not want to release too much as the space may collapse but the too little and the pedal bone will be pulled down as the hoof grows.
• MMP is a catabolic enzyme
• MMP = matrix metalloproteinase
• Laminitis is degeneration then failure of interdigitation between P3 and inside of the hoof wall leading to breakdown and separation

  • Excess MMP activity is involved
• label the image

  A) DDFT

  B) navicular bone

  C) digital cushion

  D) frog

  E) sole

  F) white line

  G) epidermal

  H) dermal

  
• Causes of laminitis are…

  • Endocrine
  • Obesity / Equine metabolic syndrome
  • Pars Pituitary Intermedia Dysfunction (PPID / Cushings)
  • Non-endocrine
  • Toxic
  • Support limb laminitis
  • Corticosteroid induced
  • Stress
• • Obesity / Equine metabolic syndrome
  • Increased bodily fat reduces the cellular response to insulin leading to insulin resistance / dysregulation. This means that cells remove less glucose from the blood stream leading to hyperglycaemia. The body produces more insulin to try to combat hyperglycaemia (negative feedback loop) causing hyperinsulinemia. The excess insulin in blood stream stimulates excess MMP production, increasing the risk of laminitis
• in Pars Pituitary Intermedia Dysfunction (PPID / Cushings) excess Adrenocorticotrophic hormone (ACTH) also causes hyperinsulinemia

  • Endocrinopathic causes of laminitis are closely interlinked
• toxic is concurrent to

  • compromised bowel e.g. colitis, enteritis, strangulation
  • 2) Severe infection e.g. retained foetal membranes /  sepsis
  • The bacterial endotoxin enters the blood stream leading to endotoxemia and hence MMP production is increased
• Severe lameness in 1 limb causes excessive weight bearing in the contra-lateral limb e.g. fracture with inadequate stabilisation. The prolonged pressure within the hoof of the ‘non-lame’ limb reduces blood flow to the laminae causing hypoxia. The hypoxia causes inflammation and MMP production.

  • Therefore support limb laminitis is often unilateral
• Exogenous glucocorticoids rarely cause laminitis (0.15%), however, they can induce hyperinsulinemia and subsequently increase MMP production. You must inform owners of this risk and document this conversation
• There is no consistent age predisposition, but foal and weanlings are rarely affected. It occurs in all breeds of horses, but native breeds / ponies are predisposed. A shire or draft breed is harder to treat as these are in general heavier breeds.

  • Donkeys can be severely affected

  There is no sex predisposition.
• laminitis is a year-round problem with incidence peaks in spring and autumn
• Most cases are endocrine, toxic and support limb less common
• History should cover…

  • When did signs begin?
  • Progression –getting better or worse?
  • Any recent management changes?
  • Pay specific attention on what the horse has been fed
  • Previous episodes of laminitis?
  • Any concurrent disease / injury?
  • Received any medications recently?
  • Current diet?
  • When last trimmed / shod?
  • Horse’s use?
  • Exercise history?
• Horses are programmed to eat grass and are efficient food convertors, however, in the wild they would be on sparse grass but we house them on lush grass designed for maximum milk yield in cows and hence is very dense for them.
• perform a general clinical exam involving…

  • Is the animal recumbent or does it have an abnormal stance?
  • Is it leaning backwards or weight shifting
  • Resp. rate / panting?
  • Heart rate?
  • This is a good way to assess pain (80bpm indicates severe pain)
  • Temperature?
  • Sweating?
  • Pained expression?
  • Also look for evidence of endocrine disease
  • Assess the distal limbs
• evidence of endocrine disease are

  A) hirsuitism

  B) pot belly

  C) fat pads

  D) fat

  
• Laminitis often affects both front limbs, all 4 limbs can be affected, just 1 limb or just the hind limbs.

  • Increased digital pulse and hooves that are warm to the touch are indicative
  • Visible growth rings indicate previous episodes (they should be parallel)
  • Is the horse able to lift the legs?
  • Laminitis cases often show pain to hoof testers at the point of frog
  • Depression at the coronary band and loss of concavity of sole suggest severe disease (sinking) while swelling and pain still indicate a case of laminitis
• It takes 6 months to grow from the coronary band to the toe so you can identify when the episodes have been when presented with abnormal hoof rings
• the degree of lameness varies in these cases, ranging from mild to severe (unable to walk). Lameness is usually worse when turning and on hard ground, the foot lands heel first to spare the toe region from weight bearing. They are often described as having a pottery gait

  • Sometimes shows a high-stepping gait with hind limb laminitis.
• a first acute case of laminitis should not be radiographed as it is too early for changes to be seen. instead wait 4 to 7 days.
• Rotation more than 5 degrees is mild, 5 to 10 degrees moderate and more than 10 degrees are severe
• On radiography, rotation / dropping of P3, remodelling / degeneration at the tip of P3 may be seen and rarely collapse on just the lateral or medial side
• what sign of laminitis can be seen in these images?


  P3 drop / rotation as well as remodelling / degeneration at the tip of P3

  
• what can be seen in this image?

  collapse on the medial side

  
• • EMS testing
  • Baseline insulin (serum)
  • Feed only hay / grass for 12 hours prior
  • Positive result (increased baseline insulin) is diagnostic for EMS
  • Negative result (normal baseline insulin) does not rule the disease out –lots of false negatives
  • Oral sugar challenge tests
  • Feed only hay / grass for 12 hours prior
  • Feed Karo light corn syrup or dextrose powder
  • Blood sample for insulin 60 to 90 mins later
• For PPID testing, perform baseline ACTH (EDTA)

  • Reference range changes through the year. Usually most accurate in the autumn
• With metabolic testing, the results are inaccurate if animal is in pain so maybe wait a few days until the horse is more comfortable. Repeated samples are required to assess the response to treatment, adjust management and drug dosages.
• butorphanol is best for short or longterm pain relief?

  short
• management involves...

  • Pain Relief NSAIDs (phenylbutazone), paracetamol, opiates (commonly butorphanol)
  • Vasodilator to improve blood supply to distal limbs
  • Acepromazine (has the additional benefit of reducing anxiety)
  • Support feet
  • Confine to stable on deep shavings bed for 3 weeks of box rest - Remove shoes?
  • Use frog supports to help get the weight of the sole
  • Icepacks in the per acute phase (not after the first 24 hours)
  • Diet - Weight loss
  • A tiny amount of low-sugar food (alfalfa) to put medication in
  • Vitamin / mineral balancer for long-term control
• for the diet ideally give 1.25 to 2% body weight dry weight hay, soaked for 1 hour to reduce sugar content
• when managing these cases warn owner that this is not a quick fix and euthanasia may be necessary.
• Subsequent management involves…

  • Adjust medication & management accordingly
  • Endocrine testing once pain reduced
  • EMS – metformin, levothyroxine, ertugliflozin
  • PPID – pergolide, cabergoline
  • Farriery – trim heels & toes, heart bar shoes
  • Carefully and gradually introduce exercise
  • Repeat radiographs if not improving / as required by a farrier
• Salvage procedure is a deep digital flexor tenotomy (only for rotational laminitis not sinking) on the mid cannon as this removes the palmar traction on P3.
• The prognosis of cases depends on…

  • Lameness severity
  • Degree of rotation
  • Sinking
  • Patient weight
  • Ability to control endocrine disease

  Improvement takes many months as the hoof grows down (1 year) and repeated episodes are common. Do not blame the owner, there is often a guilt complex as they know the horse's weight has contributed to this. it is important to have regular conversations about the pain the horse is in
• the earlier you catch laminitis the better the prognosis