Chapter 200

Managing Acute Laminitis

Stephen E. O’Grady

Acute laminitis in horses should be considered a medical emergency because of the limited time frame for effective medical intervention. Laminitis is more difficult to treat than other soft tissue injuries because the affected tissue lies within a rigid hoof, is subject to tremendous mechanical forces, and is perfused by a circulation that can readily be compromised. The challenges faced by the veterinarian include not only treating a disease with a poorly defined pathogenesis but also guiding and counseling the owner, trainer, and farrier throughout the treatment. The owner should be made aware of the difficulties associated with treating severe laminitis and the ethical considerations regarding the welfare of the horse. The goal of the clinician is to relieve pain, attempt to prevent or limit further damage to the lamellae, and improve function of the feet. The clinician is often limited in this respect because it is the extent of the lamellar pathology that limits the success of treatment rather than the treatment itself. Importantly, there is no proven or consistently effective treatment for laminitis. Consequently, treatment regimens for both acute and chronic laminitis generally remain empirical and are recommended on the basis of the past experience of the attending clinician. Each horse with acute laminitis should be approached on an individual basis, taking into consideration the history, predisposing cause, degree of pain (instability), hoof conformation, and structures of the foot that can be used to change the forces placed on the hoof.

Most horses with acute laminitis are treated at the client’s farm rather than being transported to a referral facility because moving a horse with acute unstable laminitis may worsen the existing condition. Initially, the necessary expertise, medical care, imaging equipment, and farriery care can be provided at the farm. Radiography is essential for diagnosis, assessment of foot conformation, and guidance for the initial phase of hoof care. Additional benefits of treating the horse on the farm include the familiarity of the horse with its surroundings and the familiarity of the owner and trainer with the patient. The former reduces stress on the animal, whereas the latter allows better assessment of improvement or deterioration because the owners are more familiar with the animal’s normal behavior than is the attending veterinarian. An acceptable outcome in all but the mildest cases of laminitis requires a team of dedicated individuals consisting of the veterinarian, farrier, and owner. This chapter presents an overview of the treatment options available for managing acute laminitis in an ambulatory setting.

Phases of Laminitis

Although classification of laminitis into categories of developmental, acute, and chronic phases is convenient to enhance comprehension and assist in diagnosis, treatment, and prognosis, the disease clinically is usually a continuum. The developmental stage begins with the original insult to the lamellae and ends with the onset of clinical signs such as acute lameness, strong digital pulse, heat in the feet, hoof-tester sensitivity, and a laminitic stance. The acute stage begins with the onset of clinical signs and is frequently cited as lasting 72 hours or until displacement of the distal phalanx within the hoof capsule occurs, whichever is sooner. Chronic laminitis has been associated with continuation of clinical signs or a change in position of the distal phalanx within the hoof capsule; however, when the clinical signs of acute laminitis have not markedly improved within 48 to 72 hours, the author considers the horse to be entering the chronic stage. In some horses with equine metabolic syndrome, there appears to be a derangement of the lamellae, and these horses remain painful for an extended period of time even without displacement of the distal phalanx.

Mechanism

The anatomic structure of the various tissues affected by laminitis is well documented, but despite considerable recent advances in our understanding of the pathophysiology of laminitis, much remains to be learned about the initiating events and pathways that lead to the acute symptoms. The interdigitating dermal and epidermal lamellae and their vasculature are positioned between the parietal surface of the distal phalanx and the rigid hoof capsule. The digital circulation to the distal dorsal lamellae arises from branches of the terminal arch that form the circumflex artery; the proximal dorsal lamellae are supplied by the coronary artery. Any compromise or instability in the lamellae reorients the distal phalanx, which in turn may impair the circulation. The rigid hoof capsule limits accommodation of the inflammatory effects of laminitis, especially edema, all of which results in a scenario typical of compartment syndrome as seen in other types of tissue.

Assembling the Team

Acute laminitis must be managed by a team consisting of the veterinarian, who is responsible for the overall health and welfare of the horse; the farrier, who advises and performs the appropriate trimming and shoeing; and the horse owner or trainer, who is often the primary caregiver and who makes decisions regarding treatment and is responsible for the financial obligations. If either the farrier or veterinarian is inexperienced in treating laminitis, it is prudent to seek advice from or refer the case to a more experienced clinician. If necessary, the attending veterinarian can seek consultation from a referral center and send the necessary images. The owner should be made aware that a multitude of treatments and products are purported to improve the disease, yet none has been proved effective or produces consistent results. Furthermore, there are no controlled studies documenting the efficacy of any one medical or farriery procedure. Techniques change rapidly and for the most part are empirical. The foundation for laminitis treatment therefore remains anecdotal and can vary with stage of the disease, experience of the clinician, and response of the horse. Because no treatment has been proved superior to others, frequent dialogue is important, not only between clinicians (the veterinarian and farrier), but also with the owner, who may have his or her own thoughts, opinions, theories, and previous treatment experiences. The preferred approach is to consider the individual case in light of radiographic results and decide on a treatment strategy based on medical and biomechanical principles. Client communication is one of the most important but least discussed aspects of case management. A policy of open, honest communication that tempers false expectations of success must be used. Owners should be given realistic information from the onset, including the facts that severe laminitis carries a poor prognosis; there are no proven treatments; any treatment undertaken can be extensive, expensive, and prolonged; and the end result may still be euthanasia. Given the seriousness of acute laminitis, clients will likely look into other sources for information or hope, such as the Internet, horse magazines, and support groups, regarding the management of their horse. It is imperative that the attending veterinarian is well versed in the common inquiries that will arise and is able to address them prospectively. Accurately predicting the outcome of horses with laminitis is impossible. This is understandable, given the number of variables associated with management of severe laminitis, which includes not only the feet but also the overall health of the patient in addition to client constraints. The owners should be advised that it is their responsibility to inform the insurance company immediately.

Presentation

When the veterinarian is presented with a horse with acute laminitis, three problems are encountered. First, when the animal first shows clinical signs of acute laminitis, there is no practical means of assessing the extent of laminar damage or determining whether the damage will be permanent. This is because lamellar damage develops during the developmental stage of laminitis, which precedes the onset of pain and lameness. There is no way to predict which horses in a severe laminitic episode will be treated successfully after the acute clinical signs have been observed. Second, no practical means exist for counteracting the vertical load (weight) placed on the horse’s feet: there is no practical device or method to remove the weight from the compromised lamellae. Third, the distractive force placed on the compromised lamellae by the deep digital flexor tendon (DDFT) is difficult to counteract.

Assessment

History

The importance of the medical history cannot be overemphasized. This is often overlooked by the clinician eager to treat the horse, but taking a complete history is well worth the time it requires because of the valuable information that may be obtained. The history should reveal whether the present manifestation is an initial episode, a recurrence, or an exacerbation of a continuing condition. It should also include questioning about any preexisting conditions, such as a recent surgery or colic episode, retained placenta, or a recent change in exercise routine. The environment should be taken into account, as well as season of the year. For example, fructan concentration in the grass, which is implicated as an instigating factor in pasture-associated laminitis, is highest in the spring and after heavy rainfall. Attempting to obtain an etiology from the history is always worthwhile and should include asking questions such as the following: Has the horse had a recent diagnosis of disease? What is the current feeding routine of the horse and has anything changed? Have any medications or vaccinations recently been given? Is the horse receiving any long-term medications? Has there been a history of trauma recently, or in the past, associated with the laminitis? Has the horse been subjected to a stressful event or been shipped a long distance? Answers to these questions may give clues to the cause of laminitis and how to initiate treatment.

Physical Examination

A complete physical examination with detailed evaluation of the feet is mandatory. The physical examination is performed with both the eyes and the hands of the clinician. The temperature, pulse, and respiratory rates, as well as the horse’s stance and its willingness to move, can yield information regarding the degree of pain. Observing the horse’s body and head position when the clinician lifts a limb from the ground also indicates the degree of discomfort. Assessment of the intensity of the digital pulse, temperature of the feet, and extent of lameness should be made. The coronary band should be assessed for edema, depressed areas that indicate distal displacement of the distal phalanx, and palpably tender areas that may be associated with an abscess or hoof wall separation. The shape and position of the sole is observed for degree of concavity or protrusion, soft spots, or excessive loss of depth.

The size and conformation of the feet are especially important in the designing of a farriery plan and for monitoring subtle changes associated with progression of disease. Hoof conformation may influence loading patterns and the type of displacement encountered. For example, in the author’s experience, there is generally a high potential for displacement in an upright or club foot because of the high load on the dorsal lamellae caused by the preexisting shortening of the DDFT musculotendinous unit and corresponding dorsal center of pressure in the foot. On the other hand, horses with long toe–low heel conformation generally have thin soles and limited ability to counteract the downward rotational force on the distal phalanx exerted by the horse’s weight.