Laminitis, Acute
Basic Information 
Genetics
• Pony breeds at greater risk than are horse breeds.
• Acute laminitis and sloughing of the hoof in foals is a component of junctional epidermolysis bullosa in the Belgian and American Saddlebred breeds.
• One report of laminitis in a foal resulting from inherited deficiency of the plectin protein (a critical cytoplasmic component of hemidesmosomes).
Clinical Presentation
Disease forms/subtypes
• Classification of laminitis categories
Acute laminitis: Hoof lamellar inflammation has been activated for the first time and is associated with pain.
Period of time that transpires between the onset of an acute laminitis-provoking event and the first signs of acute laminitis (eg, endotoxemia associated with acute typhlocolitis)
Pasture-associated laminitis: Acute or chronic laminitis arising in the context of grazing pasture grasses
Physical Examination Findings
• The clinical presentation of acute laminitis differs depending on which foot and in how many feet the disease develops.
• More common in adult horses than in foals (affected foals may have genetic disease).
• Most commonly presents as severe pain affecting both forelimbs.
• Pain-associated conjunctival membrane injection
• Characteristic apprehensive facial expression
• Subcutaneous edema of the distal limbs (because of reduced mobility)
• Affected feet are often warm
• Digital arterial pulses are very prominent (“bounding” pulses)
• Reluctance to move or to stand up
• When forced to stand and bear weight, stiffness and a characteristic stance make it clear that acute laminitis has developed.
• Horses stop moving around in their environment.
• Tendency to “oscillate in situ” (attempting to seek a comfortable stance by transferring the center of gravity toward the pelvis and shifting the weight between both forelimbs).
• The pelvic limbs are drawn forward under the body and both forelimbs are extended out in front of the body.
• Horses walk in a manner such as to reduce weight bearing by the dorsal aspect (toe) of the forefeet, preferring to extend the forelimbs and bear greater weight at the heel.
• Walking movements are careful, slow, and deliberate, and the patient tends to bear increased weight in the pelvic limbs, giving rise to the descriptor “walking on eggshells.”
• Systemic signs of pain such as sweating, trembling, muscle fasciculations, and rapid breathing
• Shaking of the affected limbs (especially affected pelvic limbs)
• Hoof pain is accentuated by turning sharply on a hard surface.
• Moving affected horses on hard surfaces may worsen laminitis and convert subtle signs of stiffness and lameness into a more severe and clinically prominent manifestation.
• Serosanguineous discharge at the coronary band (intracapsular necrosis)
• Sloughing of the affected hoof or hooves (exunguilation)
• Unwillingness to bear weight on the opposite affected hoof (difficult to pick up the foot)
• “Resting” the opposite limb after one hoof has been picked up for examination and released
• The strength of the digital arterial pulses increases during the examination as a result of forcing the patient to bear weight.
• Coronary band develops a trough/shelf or depression
• Hemorrhage at the coronary band (coronary vessel rupture)
• Hoof testers yield a pain reaction at the toe (both false-positive and -negative reactions to hoof testers)
• Signs of preexisting laminitis may be evident, including prominent circumferential growth rings in the hoof wall, palmar or plantar divergence of growth rings, broadening of the white line zone, and the development of a “dropped” sole.
• Conservative paring of the sole may reveal flecks of hemorrhage as a result of either chronic or acute laminitis.
• Sudden or unanticipated “improvement” in the extent to which weight is borne by the primary limb during fracture management (implicative for laminitis in the contralateral limb)
• Laminitis may develop in one hoof when a sufficiently severe inflammatory process is present within the hoof for other reasons (eg, unresolved sole abscesses, nail or other foreign body penetrations, or exercise on hard surfaces [“road founder”]).
Diagnosis 
• Inspection and physical examination of all four feet
• Plain film radiography is essential for purposes of corroborating the diagnosis, characterizing the severity and extent of laminitis, and establishing the baseline appearance of the affected foot for purposes of monitoring responses to treatment and making a prognosis.
Radiographic Characterization
• It is important to emphasize the value of a meticulous approach for the acquisition of valuable and meaningfully diagnostic radiographic images.
• Acquisition of helpful radiographic metrics necessitates excellent lateromedial projection technique.
• Zero hoof-to-film distance minimizes magnification and standardizes the resulting images for serial comparisons during treatment.
• Use a radiopaque marker at the dorsal aspect of the hoof (starting at the point at which the coronary band connects with the hoof wall).
• Specific components of the lateromedial view of the equine hoof that should be carefully scrutinized include:
The palmar/plantar angle of the third phalanx (angle of palmar margin of the third phalanx relative to the bearing surface of the hoof)
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