David M. Hood

The Pathophysiology of Developmental and Acute Laminitis

This review implies that although we know more regarding the enigma of developmental and acute laminitis today than previously, there is still more to investigate. As these investigations are conducted and interpreted, new and more effective preventive and therapeutic regimens are likely to be developed, tested, and made available. As this occurs, the impact of laminitis should undoubtedly decrease. Unfortunately, due to the lack of clinical symptoms in the developmental phase and the shortness of the acute phase, it is also evident that the two sequelae of acute laminitis, subacute and chronic laminitis, are likely to continue to pose a major problem for some time.

A multicenter, matched case-control study of risk factors for equine laminitis

Risk factors for equine laminitis were examined in a prospective case-control study of the 258 cases seen at six collaborating veterinary teaching hospitals over a 32-month period. Case-control pairs were matched on institution, clinician, and season of diagnosis. The 90% of case-control pairs (78 acute, 155 chronic) that had complete data for age, gender, and breed were used in separate conditional logistic-regression models for acute and chronic laminitis. There was an increase in risk for horses with acute laminitis from 5 to 7 years of age (OR 4.7, 95% CI 1.3-16) and from 13 to 31 years of age (OR 3.9, 95% CI 1.3-12) (both compared to <5 years); risk was increased for chronic laminitis from 10 to 14 years (OR 3, 95% CI 1.4-6.8) and from 15 to 38 years (OR 2.9, 95% CI 1.4-6.1) (both compared to <6 years). Mares - but not stallions - were more likely than geldings to develop acute laminitis (OR 2.6, 95% CI 1.1-6.2) and chronic laminitis (OR 2.0, 95% CI 1.1-3.6). In the small acute-laminitis data set, the breed variable was collapsed into three categories: Thoroughbred (THB, reference), the Quarter Horse (QH), and other (non-QH-THB). The non-QH-THB group was at increased risk of acute laminitis (OR 3.8, 95% CI 1.2-11.8). For the seven breed-group categories used in the chronic-laminitis model, however, all non-THB breed groups appeared significantly at risk as compared to the THB, with odds ratios ranging from 3.3 (95% CI 1.3-8.30) for the QH to 9.1 (95% CI 2.1-39.3) for ponies.

The Mechanisms and Consequences of Structural Failure of the Foot

Many of the difficulties in managing the horse with chronic laminitis are associated with the foots mechanical failure. The occurrence of digital collapse cannot be viewed in isolation as the primary therapeutic focus. The circulatory, metabolic, and growth pattern changes induced by the foots mechanical collapse often serve as major limiting factors to successful rehabilitation. From the discussion above, it is obvious that a significant amount of research is needed to better understand the biomechanical pathologies of the failed foot.

Laminitis in the Horse

This article serves as an introduction to this issue on laminitis. As such, it contains the general perspectives and terminology that will be used in all subsequent articles. This article separates the clinical problem of laminitis into developmental, acute, subacute, and chronic phases and defines the criteria, duration, clinical goals, and implications of these phases. The basis for the significance of laminitis to the horse industry and the horseman is reviewed. Lastly, the organization of this issue is described.

Equine Laminitis: A Potential Model of Raynaud's Phenomenon

Raynauds phenomenon (RP) and equine laminitis in the horse are medical enigmas. Clinical and scientific data were compared to evaluate the degree of similarity that exists between these two peripheral vascular diseases. Data indicate that certain pathologic and pharmacologic aspects seem to have common features. Some of the correlations maybe due simply to both diseases having ischemia of the distal digits as a pathologic component. The exact etiology of the ischemia is not known for either disease. The results of this study suggest the hypothesis that RP and laminitis are the same disease in different species. This hypothesis can be tested more efficiently when the pathophysiology of both conditions is better documented. It is possible that comparative studies will promote advances in the understanding of both RP and laminitis. The fact that equine laminitis can be experimentally induced is of potential value in such future studies.

Clinical presentation, diagnosis, and prognosis of chronic laminitis.

This article focuses on the initial assessment of the horse affected with chronic laminitis. Variations in the clinical presentation and primary considerations in making a differential diagnosis are included. The elements of a clinical history essential to sound, therapeutic management, and prognosis are summarized. The physical and radiographic assessment of the digital lesions and diagnostic approaches to the common systemic aspects of the disease are presented and discussed.

Laminitis as a Systemic Disease

This article presents the clinical pathology and the involvement of the cardiovascular, renal, endocrine, and immunologic systems in laminitis. The data available on these systems are presented with respect to the disease phase and severity. The nutritional and metabolic alterations realized in the chronically affected horse are also presented. In this discussion, the origins and clinical implications of these systemic findings are discussed.

Effect of ketamine hydrochloride on the analgesic effects of tramadol hydrochloride in horses with signs of chronic laminitis- associated pain

OBJECTIVE To investigate the effects of ketamine hydrochloride on the analgesic effects of tramadol hydrochloride in horses with signs of pain associated with naturally occurring chronic laminitis. ANIMALS 15 client-owned adult horses with chronic laminitis. PROCEDURES Each horse received tramadol alone or tramadol and ketamine in a randomized, crossover study (≥ 2 months between treatments). Tramadol (5 mg/kg) was administered orally every 12 hours for 1 week. When appropriate, ketamine (0.6 mg/kg/h) was administered IV for 6 hours on each of the first 3 days of tramadol administration. Noninvasive systemic blood pressure values, heart and respiratory rates, intestinal sounds, forelimb load and off-loading frequency (determined via force plate system), and plasma tumor necrosis factor-α and thromboxane B(2) concentrations were assessed before (baseline) during (7 days) and after (3 days) each treatment. RESULTS Compared with baseline data, arterial blood pressure decreased significantly both during and after tramadol-ketamine treatment but not with tramadol alone. Forelimb off-loading frequency significantly decreased during the first 3 days of treatment with tramadol only, returning to baseline frequency thereafter. The addition of ketamine to tramadol treatment reduced off-loading frequency both during and after treatment. Forelimb load did not change with tramadol alone but increased with tramadol-ketamine treatment. Plasma concentrations of tumor necrosis factor-α and thromboxane B(2) were significantly reduced with tramadol-ketamine treatment but not with tramadol alone. CONCLUSIONS AND CLINICAL RELEVANCE In horses with chronic laminitis, tramadol administration induced limited analgesia, but this effect was significantly enhanced by administration of subanesthetic doses of ketamine.

The Pathophysiology of Chronic Laminitis: Pain and Anatomic Pathology

The potential pathologic manifestations of chronic laminitis are just as varied, and possibly more so, than the list of possible inciting agents of the disease itself. The extent to which rehabilitation and return to normal function can be attained, cannot always be accurately determined by physical examination. It should be remembered that significant physiologic and pathologic alterations occur in chronic laminitis; thus, even if radiographically the patient returns to a normal appearance, residual morphologic and structural defects are likely to remain.

The Digital Pathologies of Chronic Laminitis

This review indicates that the patient-to-patient uniqueness commonly seen in chronic laminitis represents the variable presence of the digital pathologies. Although some degree of mechanical failure is always present, the secondary metabolic and growth dysplasias, vascular pathologies, and sepsis may or may not be evident. The presence and severity of these pathologies appear to have a more significant impact on the prognosis of individual cases than does the displacement of the distal phalanx. It should be reiterated that it is often the combined presence of these individual pathologies that gives rise to the patient that is totally refractory to treatment. In the absence of these pathologies, many horses with significant displacement of the distal phalanx are not in pain and are not in need of treatment. It thus follows that a key to the improved rehabilitation of difficult patients is focusing research on the physiopathology and diagnosis of these nonmechanical problems.