Laminitis

Question 1

Definition

Answer 1

• inflammation of the laminae of the foot

Question 2

Founder

Answer 2

• laminitis so severe that all the laminae in the hoof cease functioning and the pedal bone has dropped down
  BUT
• term used interchangeably with laminitis

Question 3

What is the weight bearing structure of the hoof?

Answer 3

• the hoof wall
• (the frog takes some of it)

Question 4

What are the 2 types of laminae in the hoof

Answer 4

• sensitive laminae (attached to the coffin bone)
• insensitive laminae (attached to the hoof wall)

Question 5

Pathophysiology

Answer 5

• 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)
• MMP are catabolic enzymes
• laminitis is the degeneration then failure of interdigitation between P3 and inside of hoof wall -> breakdown & separation
• excess MMP activity is involved
• mechanisms not fully understood but several dz processes are implication
• sliding scale of severity (not a binary dz)

Question 6

Where does hoof wall grow from?

Answer 6

• the coronary band

Question 7

How long does it take the hoof wall to grow from the coronary band to the sole?

Answer 7

• 6m
• less (~4m) for the palmar/plantar aspect

Question 8

Endocrine causes

Answer 8

• EMS
• PPID

Question 9

Non-endocrine causes

Answer 9

• toxic
• support limb laminitis
• corticosteroid induced

Question 10

Obesity/EMS causing laminitis

Answer 10

• increased bodily fat reduces the cellular response to insulin -> insulin resistance/dysregulation
• cells remove less glucose from bloodstream ->hyperglycaemia
• body produces more insulin to try to combat the hyperglycaemia (negative feedback loop) -> hyperinsulinaemia
• excess insulin in bloodstream stimulates excess MMP production increasing the risk of laminitis

Probably the most common cause of laminitis

Question 11

Toxic causes of laminitis

Answer 11

concurrent to:
1. compromised bowel e.g. colitis, enteritis, strangulation
2. severe infection e.g. RFM/sepsis

• bacterial endotoxin enters the bloodstream -> endotoxaemia
• MMP production is increased

Question 12

PPID causing laminitis

Answer 12

• excess ACTH also causes hyperinsulinaemia
• endocrinopathic causes of laminitis are closely interlinked

Question 13

Support limb laminitis

Answer 13

• severe lameness in 1 limb causes excessive weight bearing in contra-lateral limb, e.g. fracture with inadequate stabilisation
• prolonged pressure within the hoof of the ‘non-lame’ limb reduces blood flow to the laminae causing hypoxia
• hypoxia causes inflammation and MMP production
• therefore, support limb laminitis is often unilateral

Question 14

Corticosteroid induced laminitis

Answer 14

• exogenous glucocorticoid
  – rare (0.15% in a study)
  – different glucocorticoids have different risks, e.g. preds very low, others (e.g. triamcinolone) much higher
• stress
  – endogenous glucocorticoids increase
• induce hyperinsulinaemia and subsequent increased MMP production
• risk greater in animals that are already susceptible e.g. EMS
• discuss this risk with O before corticosteroid injection
• recommend taking blood insulin test before administering corticosteroids (even for asthma) in fat horses

Question 15

Signalment

Answer 15

Age
- no consistent predisposition but foal & weanlings rarely affected (likely bc they’re growing so all their glucose is going into growing, also they’re not old enough for the endocrine disorders)

Breeds
- occurs in all breeds of horse, but natives/ponies predisposed
- donkeys can be severely affected
- the heavier the horse the more difficult it will be to treat, e.g. draughts/shires

Sex
- no predisposition

Question 16

Incidence in UK

Answer 16

• 1/10 equines may have at least 1 laminitis epidote each year
• as common as colic
• approx. 15% equine deaths linked to laminitis
• year round problem with incidence peaks in spring and autumn
• most cases are endocrine
  – toxic and support limb less common

Question 17

History q’s

Answer 17

• when did signs begin?
• progression - getting better or worse?
• any recent management changes?
• previous episodes of laminitis?
• any concurrent dz/injury?
• received any medications recently?
• current diet?
• when last trimmed/shod?
• horse’s use?
• exercise history?

Question 18

General CE

Answer 18

• recumbent?
• stance?
  – leaning backwards
  – weight shifting
• rr/panting?
• hr?
• temp?
• sweating?
• pained expression?

Question 19

CE - evidence of endocrinopathy

Answer 19

PPID
- hirsutism
- decreased muscle mass
- ‘pot belly’ appearance
- supraorbital fat pads

EMS
- excess body condition
- abnormal fat distribution

Question 20

CE - limb specific

Answer 20

• often affects both front limbs
• may be all 4 limbs, just 1 or just the hind limbs
• increased digital pulse
• hooves warm to touch
• visible growth rings indicate previous episodes
• able to life legs?
• often show pain to hoof testers at point of frog
• shod/unshod and type of shoe?
• depression at coronary band and loss of concavity of sole suggest severe dz (sinking)

Question 21

CE - dynamic

Answer 21

• degree of lameness varies
• may be mild (walks almost normally) to severe (unable to walk)
• usually worse when turning and on hard ground
• foot lands heel first to spare the toe region from weight bearing
• sometimes show a high stepping gait with hind limb laminitis

Question 22

Modified Obel grade 0

Answer 22

• sound

Question 23

Modified Obel grade 1

Answer 23

• weight shifting at rest
• sound walking in straight line
• stilted gait when turning or trotting

Question 24

Modified Obel grade 2

Answer 24

• stilted gait when walking in straight line
• clearly lame when turning
• legs can be lifted without difficulty

Question 25

Modified Obel grade 3

Answer 25

- reluctant to walk - legs can only be lifted with great difficulty

Question 26

Modified Obel grade 4

Answer 26

- will only move if forced to - spends long periods recumbent

Question 27

Radiography

Answer 27

Latero-medial view - rotation -- <5° mild -- 5-10° moderate -- >10° severe - sinking - remodelling/degeneration at tip of P3? - hoof overgrowth? Dorso-palmar view - rare collapse on just the lateral or medial side

Question 28

Metabolic testing - EMS

Answer 28

1) 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 2) Oral sugar challenge tests - Feed only hay / grass for 12 hours prior - Feed Karo light corn syrup or dextrose powder - Blood sample for insulin 60-90 mins later

Question 29

Metabolic testing - PPID

Answer 29

1) Baseline ACTH (EDTA) - Usually diagnostic - Reference range changes through the year - Usually most accurate in the autumn 2) Thyrotropin Releasing Hormone stimulation test - Rarely required - Collect baseline ACTH - Inject TRH - Collect another ACTH 10 minutes later

Question 30

Metabolic testing

Answer 30

▪ Results are inaccurate if animal is in pain – maybe wait a few days until more comfortable. ▪ Repeat samples are required to assess the response to treatment and adjust management & drug dosages

Question 31

Initial Management

Answer 31

▪Pain Relief - NSAIDs (phenylbutazone), paracetamol, opiates (butorphanol good for short term analgesia) ▪ Vasodilator - Improve blood supply to distal limbs - Acepromazine (has additional benefit of reducing anxiety) ▪Support feet - Confine to stable on deep shavings bed - Remove shoes? - Use frog supports - In the per-acute phase (not after 24h) ice packs can help ▪ Diet - Weight loss - 1.5-2% body weight dry weight hay, soaked for 1 hour to reduce sugar content - Tiny amount of low sugar food (alfalfa) to put medication in - Vitamin / mineral balancer ▪ Warn owner that this is not a quick fix - 3w bost rest minimum to start with ▪ Euthanasia?

Question 32

Subsequent management

Answer 32

▪ Regular re-examinations (initially 1x weekly) ▪ Adjust medication & management accordingly ▪ Endocrine testing once pain reduced ▪ EMS – metformin, levothyroxine, ertugliflozin ▪ PPID – pergolide, cabergoline ▪ Farriery – trim heels & toes, heart bar shoes (good as utilises the frog to reduce weight bearing on the sole) ▪ Carefully and gradually introduce exercise ▪ Repeat radiographs if not improving / as required by farrier ▪ Euthanasia?

Question 33

Salvage procedure

Answer 33

▪ Deep digital flexor tenotomy ▪Mid cannon ▪ Removes the palmar traction on P3 ▪ Salvage only (some believe) ▪ Only for rotational laminitis ▪ Instantly reduces lameness by 1 Obel grade

Question 34

Prognosis

Answer 34

▪ Lameness severity ▪Degree of rotation ▪ Sinking ▪Patient weight ▪ Ability to control endocrine disease ▪ Improvement takes many months - As the new hoof grows down – 1 year ▪ Repeat episodes are common