Laminitis Flashcards
What is laminitis?
Laminitis is inflammation of the laminae of the foot - also called ‘founder’
Laminae are intricate interdigitated tissues from inside of hoof and outside of P3
What is the pathophysiology behind laminitis?
- 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 degeneration then failure of interdigitation between P3 and inside of hoof wall → breakdown & separation
- Excess MMP activity is involved
- causes rotation of the pedal bone to take place - due to the pull of the DDFT on the pedal bone towards the sole
What causes laminitis to develop?
Endocrine
Obesity / Equine Metabolic Syndrome
* Increased bodily fat reduces the cellular response to insulin – insulin resistance / dysregulation
* Cells remove less glucose from blood stream – hyperglycaemia
* Body produces more insulin to try to combat hyperglycaemia (negative feedback loop) – hyperinsulinaemia
* Excess insulin in blood stream stimulates excess MMP production increasing the risk of laminitis
Pars Pituitary Intermedia Dysfunction (PPID / Cushings)
* Neoplasia of the pituitary gland causing excess Adrenocorticotrophic hormone (ACTH) also causes hyperinsulinaemia
* Endocrinopathic causes of laminitis are closely interlinked
Non-endocrine
Toxic
Concurrent to
* compromised bowel e.g. colitis, enteritis, strangulation
* Severe infection e.g. retained foetal membranes / sepsis
* Bacterial endotoxin enters the blood stream – endotoxaemia
* MMP production is increased
Support limb laminitis
* 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
Corticosteroid induced
- exogenous glucocorticoid - rare, 3/2000 (0.15%) Triamcinolone
OR
- Stress - endogenous glucocorticoids increase
- Induce hyperinsulinaemia and subsequent increase MMP production as above
- Risk greater in animals that are already susceptible
What signalment is most common with laminitis?
Age – No consistent predisposition, but foal & weanlings rarely affected
Breed - Occurs in all breeds of horse, but native breeds / ponies predisposed
- Donkeys can be severely affected
Sex – No predisposition
What is the incidence of laminitis in the UK?
- 1 in 10 equines may have at least 1 laminitis episode each year - as common as colic
- Approximately 15% equine deaths are linked to laminitis
- Year round problem with incidence peaks in spring & autumn
- Most cases are endocrine - toxic and support limb less common
What history questions should you ask when investigating a laminitis case?
- 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?
What should you assess in your general clinical exam when investigating a case of laminitis?
- Recumbent?
- Stance?
- leaning backwards
- weight shifting
- Resp. rate / panting?
- Heart rate?
- Best to monitor pain
- Temperature?
- Sweating?
- Pained expression?
- ears back, dilated nostrils
What findings in your clinical exam would suggest endocrine disease?
PPID
* hirsuitism
* decreased muscle mass
* ‘pot belly’ appearance
* supra orbital fat pads
EMS
* excess body condition
* abnormal fat distribution
How many limbs are usually affected by laminitis?
- Often affects both front limbs
- May be all 4 limbs, just 1 limb or just the hind limbs
What should you include in your exam of the limbs? What clinical signs do you expect in the limbs affected by laminitis?
- Able to lift legs?
- Shod / unshod and type of shoe?
Findings
* Increased digital pulse
* Hooves warm to touch
* Depression at coronary band and loss of concavity of sole suggest severe disease (sinking)
* Often show pain to hoof testers at point of frog
* Visible growth rings indicate previous episodes
What do you expect to see in a dynamic exam investigating laminitis?
- 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.
What grading system is used to describe laminitis?
0 - Sound
1 - Weight shifting at rest
- Sound walking in straight line
- Stilted gait when turning or trotting
2 - Stilted gait when walking in straight line
- Clearly lame when turning
- Legs can be lifted without difficulty
3 - Reluctant to walk
- Legs can only be lifted with great difficulty
4 - Will only move if forced to
- Spends long periods recumbent
What radiographic views should you take when investigating laminitis? What can you assess?
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
How can you test for EMS?
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
How would you test for PPID?
1) Baseline ACTH (EDTA - purple)
* 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
What does the prognosis associated to laminitis depend on?
- Lameness severity
- Degree of rotation
- Sinking
- Patient weight
- Ability to control endocrine disease
