26.5.4: Laminitis Flashcards
What are laminae and what is their purpose?
Laminae: intricate interdigitated tissues from the inside of the hoof and outside of P3.
- Horses don’t stand on their sole; they “hang” from the inside of the hoof wall
Pathophysiology of laminitis
- Dermal lamellae (P3) and epidermal lamellae (hoof) are strongly bonded
- To allow hoof growth this bond is released slightly via the active of metalloproteinase (MMP; a catabolic enzyme)
- Laminitis is degeneration, then failure of interdigitation between P3 and the inside of the hoof wall -> breakdown and separation
- Excess MMP is involved
- Mechanisms not fully understood but several disease processes implicated
Risk factors for laminitis
- Obesity / EMS
- PPID
- Toxins
- Contralateral limb lameness
- Corticosteroids (endogenous and exogenous)
Laminitis signalment
- Age: no consistent predisposition but foals and weanlings rarely affected
- Breed: all can be affected but native breeds / ponies predisposed
- Sex: no predisposition
- Donkeys also suffer and hide pain well so are often severely affected by the time of detection
How can obesity / EMS lead to laminitis?
- Increased body fat reduces the cellular response to insulin -> there is insulin resistance / insulin dysregulation
- Cells remove less glucose from the bloodstream -> hyperglycaemia
- Body produces more insulin to try to combat the hyperglycaemia (negative feedback loop) -> hyperinsulinaemia
- Excess insulin in the bloodstream -> stimulates MMP production -> increased risk of laminitis
How can PPID lead to laminitis?
- Excess ACTH also causes hyperinsulinaemia
- Endocrinopathic causes of laminitis are closely interlinked
How can toxins lead to laminitis?
- Can be toxins secondary to compromised bowel e.g. colitis, strangulation
- Can be bacterial endotoxins from severe infection (e.g. RFM, sepsis)
- Endotoxaemia stimulates MMP production -> increased risk of laminitis
How can lameness lead to laminitis in the contralateral foot?
- Severe lameness in 1 limb (e.g. fracture with inadequate stabilisation) causes excessive weight bearing in the contralateral limb
- Prolonged pressure within the hood of the non-lame limb reduces the bloodflow to the laminae causing hypoxia
- Hypoxia causes inflammation and MMP production -> laminitis
How can corticosteroids (exogenous or endogenous) lead to laminitis?
- Glucocorticoids induce hyperinsulinaemia
- This leads to increased MMP production -> laminitis
- Do not give a horse steroids if they have alrready had / are in a laminitic episode. Always warn all owners about the risk of laminitis.
History questions to ask the owner of a suspect laminitic horse
- When did signs begin?
- Progression - getting better or worse?
- Any recent management changes?
- Previous episodes of laminitis?
- Any concurrent disease / injury?
- Received any medications recently?
- Current diet?
- When last trimmed / shod?
- Horse’s use?
- Exercise history?
Why do annual UK laminitis cases peak in spring and slightly in autumn?
- Due to climate conditions (rain and sun from spring-summer means grass has higher sugar content)
- Most cases of laminitis are endocrine; toxic and support limb lameness less common
- Laminitis is as common as colic with 1/10 horses affected annually
What is wrong with this horse and what will you look for on clinical exam of the laminitic horse?
Classic stance for severe laminitis
* Pain is down the dorsal aspect of the hoof hence rocking backwards
* Elevated RR due to pain
* Expression: sunken eyes, ears back, lips tight
What disease do these images suggest?
PPID
* Hirsuitism
* Decreased muscle mass
* ‘Pot-belly appearance
* Supraorbital fat pads
* Generally rare in horses less than 10-12 y.o.
What disease does this image suggest?
EMS
* Cresty neck
* Excess body condition
* Abnormal fat distribution
* Seen in any age except foals
On clinical exam of the laminitic horse, how will you work out which feet are affected?
- Hooves will be warm to touch and will have increased digital pulse
- May be all 4 limbs, or just 1 affected. Most commonly = bilateral front legs
What does this indicate?
These are growth rings - indicate abnormalities of hoof growth due to stress or disease anywhere in the body. In this case, represent previous cases of laminitis.
You are using hoof testers to assess a laminitic horse. Where would you expect them to be most reactive?
- Laminitic horses = most painful at point of frog as this is where the pedal bone is squeezing on the sole
- Tend not to show as much pain around the white line
What findings might you see on dynamic exam of the laminitic horse?
Feet landing heel first and short strides
* Degree of lameness varies
* May be mild (almost normal) or severe and unable to walk
* Usually worse when turning
* Usually worse on hard ground
* Foot lands heel first to spare the toe region from weight bearing
* Sometimes show a high-stepping gait with hindlimb laminitis
How can we grade laminitis?
Modified Obel grading system - different to normal lameness grading
What is the “rasputin slipper” radiographic finding and what does it tell you about a case?
- This indicates chronicity and multiple episodes of laminitis
- There is rotation and the tip of P3 is being destroyed (there is visible lysis and remodelling)
What is key to examine when looking at laminitis radiographs and how will you assess this?
Must assess pedal bone position
* The green lines should be parallel (i.e. there should be no rotation of the pedal bone, and it should not sink)
* <5° = mild, 5-10° = moderate, >10° severe
Why does the pedal bone position change in laminitis?
- The dorsal aspect of the pedal bone has no support
- Normally, there is equilibrium between the pull of the DDFT (pulling the pedal bone backwards) and the dorsal laminae
- When there is laminitis, the dorsal laminae are knocked out and equilibrium is disrupted
True/false: pedal bone rotation can improve slightly through treatment and management of laminitis.
True but bony changes like lysis and new bone growth will not be fixed.
What is shown here and why has it occurred?
- =collapse of the medial side of the hoof due to loss of laminae attachment -> one side of the pedal bone has collapsed
- This can happen due to abnormal conformation e.g. all the weight passing down the medial side of the leg
- This is uncommon
Which radiographic view is shown here?
Dorsopalmar/dorsoplantar
Which radiographic view is shown here?
Lateromedial
Testing for Equine Metabolic Syndrome
Baseline insulin (Serum)
* Feed only hay / grass for 12 hrs prior
* Positive result (increased baseline insulin is diagnostic for EMS)
* Negative result (normal baseline insulin) does not rule out EMS; false -ves are common
Oral sugar challenge tests
* Feed only hay / grass for 12hrs prior
* Feed Karo light corn syrup or dextrose powder
* Blood sample for insulin 60-90 mins later
Why do we feed roughage rather than concentrates before testing for EMS?
Concentrate diet -> insulin will be increased anyway.
Want to feed roughage so that if insulin is increased, we know this is abnormal (therefore EMS)
Testing for PPID
Baseline ACTH (EDTA)
* Usually diagnostic
* Ranges change throughout the year
* Usually most accurate in autumn
Thyrotropin releasing hormone (TRH) stim test
* Rarely required
* Collect baseline ACTH, inject TRH, and collet another ACTH 10 mins later
When might the results of PPID testing be inaccurate?
- If the animal is in pain (stress -> high ACTH)
- Repeat samples are required to assess response to treatment and assess management and drug doses
Initial management of laminitic horse
- Pain relief - NSAIDs e.g. phenylbutazone optimal for ortho pain. Can use opioids if in hospital.
- Vasodilator to improve blood supply to distal limb e.g. ACP (+ anxiolytic effect helpful)
- Support feet - confine to stable, can remove shoes if possible and use frog supports. Provide deep bedding to encourage lying down.
- Diet - remove grass, feed only hay (1.5-2% BW, soaked for 1hr to reduce sugar content). Provide vitamin / mineral balancer, can give tiny low sugar food e.g. alfalfa to put meds in.
- Warn the owner this is not a quick fix. Consider euthanasia.
What is pictured here and how does it help the laminitic horse?
Frog support - rubber pad that provides something soft to stand on.
* This allows the horse to stannd on their heels but with less pain, avoiding them putting pressure through the painful dorsal hoof wall.
If a horse has laminitis in March, when can it go back to grass?
Not until August or September
Long term management of mastitis
- Regular re-exams, first 48-72hrs later, then 5 days, then 2 weeks
- Adjust medication and management according
- Endocrine testing once pain reduced
- EMS: metformin, levothyroxine, ertugliflozin
- PPID: pergolide, cabergoline
- Farriery: trim heels and toes, heart bar shoes
- Carefully and gradually reintroduce exercise
- Repeat radiographs if no improvement / as required by farrier
- Consider euthanasia
What is this?
Heart bar shoe - this distributes pressure over the frog so the horse has something to stand on
What salvage procedure can be performed in the laminitic horse and when would it be done?
What determines prognosis in laminitis?
- Lameness severity
- Degree of rotation
- Sinking
- Patient weight - 5° rotation in a Shire is much worse than in a Shetland
- Ability to control endocrine disease
Improvement takes many months as the new hoof grows down over the year (hoof and bone won’t reattach, you need new hoof). Repeat episodes are common.
When should you ice the feet of a laminitic horse?
- Ice feet as prevention (e.g. mare with RFM) to try and reduce MMP production
- Do not ice feet once the horse has laminitis -> by this point we want vasodilation and more blood to the feet
