EQUINE VETERINARY EDUCATION / AE / FEBRUARY 2022


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Dyson 2010b; Weaver 2011). An example of performance- limiting urogenital problems in geldings is post-castration complications such as formation of painful neuromas at the testicular nerves or painful adhesions of the spermatic cord stump which has been suggested as the cause for inguinal pain and unexplained hindlimb lameness (Echte et al. 2006; Bengtsdotter et al. 2019). Lastly, it is important to recognise that behavioural and


performance issues are not necessarily related to an underlying clinical condition in the horse, but may be due to a riding or training problem or simply lack of athletic ability, which should also always be taken into consideration in the clinical assessment (Dyson 2010a, 2016a).


Diagnostic approach


Nonspecific performance and rideability issues in horses encompass a broad and disparate differential diagnosis. Navigating the diagnostic challenge and establishing an accurate diagnosis are therefore dependent on the use of a systematic diagnostic approach. Important steps in the process of diagnosing horses with performance or behaviour problems include obtainment of a comprehensive history, performing a complete clinical examination, performing various diagnostic tests, and referring or consulting with other equine clinicians (Davidson 2015; Dyson 2016a, 2016b). When signs are suspected to be pain-related, particular emphasis should be placed on delineating the cause of pain as musculoskeletal, oral or visceral in origin, with focus on ruling out the most common aetiologies before considering more rare causes. Figure 1 presents the proposed diagnostic methods and tools for the evaluation of pain-related causes of performance and rideability issues in horses. Musculoskeletal pain is the most common cause for poor


performance and rideability issues, underlining the importance of a thorough orthopaedic examination (Gaughan 1996; Dyson 2010a, 2016a, 2016b; Davidson 2015). Gait evaluation is a key aspect of the orthopaedic examination and should include an assessment of the horse moving in hand, on the lunge, and ridden, as well as an assessment of the response to flexion tests (Ross 2010; Dyson 2010a, 2016a). The ridden examination is indispensable, since many performance problems and lamenesses are invariably worse or only apparent when the horse is ridden (Dyson and Murray 2003; Licka et al. 2010; Dyson 2010a, 2016a; Dyson and Greve 2016). Ideally, the horse should be assessed ridden by the regular rider in its usual tack, performing the specific manoeuvres or movements with which the rider is experiencing difficulties, in order to achieve complete insight of the presenting complaint (Dyson 2010a, 2016a). The gait evaluation requires a great understanding of the biomechanics of equine locomotion and an ability to recognise low-grade gait abnormalities or other behavioural changes that are a manifestation of pain (Gaughan 1996; Dyson 2010a). This is particularly important since subjective lameness evaluation is prone to experiential bias and has a relatively low inter-observer reliability, especially for horses presenting only mild lameness (Fuller et al. 2006; Keegan et al. 2010). Recently developed wireless inertial sensor systems that objectively identify and quantify lameness could potentially serve as a helpful complementary tool to detect subtle lameness (McCracken et al. 2012; Keegan et al. 2013). Findings on the clinical evaluation may raise suspicion of


potential pain sources, which can then be investigated further by using diagnostic analgesia techniques (e.g. perineural nerve blocks, intrasynovial joint/sheath/bursa blocks or local infiltration) to truly authenticate and localise the site of pain (Dyson 2010a; Barker 2016; Brown et al. 2020). Once the site of pain has been identified, appropriate diagnostic imaging is often required to establish a definitive diagnosis (Dyson 2016a). However, it is important to realise that some anatomical areas are difficult or even impossible to block, sometimes rendering diagnostic analgesia inconclusive. Therefore, in cases where a thorough investigation has led no closer to a diagnosis, a nuclear scintigraphic examination of the horse might be helpful in localising the site of pain. Determining the clinical significance of the results of scintigraphic examination can, however, be challenging, primarily because a negative result does not preclude significant pathology and because increased radio- pharmaceutical uptake is not necessarily synonymous with pain (Archer et al. 2007; Dyson 2010a, 2016a). The results of scintigraphic examination must therefore be carefully interpreted in conjunction with findings from the clinical examination and other diagnostic tests (Archer et al. 2007; Dyson 2010a). In underperforming horses that appear clinically normal, it might also be valuable to assess the response to systemically administered analgesic drugs to try to establish if the complaint is indeed pain-related (Dyson 2010a, 2016a; Gleerup 2019). The concept of ’systemic analgesic testing’ has become relatively common within the last 5–10 years and is based on the same concept as diagnostic analgesia used in standard orthopaedic work-up. However, to the authors’ knowledge, no studies have investigated or documented the use of systemic analgesic testing for diagnostic purposes, and therefore, its application and interpretation warrant some discussion. Generally, systemic analgesic testing will be applied in horses with a longstanding problem, wherefore it might take time to achieve a response. The authors recommend systemic treatment with flunixin meglumine or meloxicam for 10– 14 days prior to concluding that the test was negative. If the performance improves and/or the behavioural problem disappears with systemic analgesia, it is a strong indication that the problem is pain-related. The negative response to this test is, however, still inconclusive, since the type of analgesia, the dosing regimen and/or the duration may be insufficient to alleviate the pain. Performing a neurologic examination is another important part of the work-up since many causes of lameness have both a musculoskeletal component and a neurologic component (Maas 2008). Hence, it is often indicated to perform various neurologic tests that assess strength and proprioceptive functions, such as sway reaction tests and limb placement tests, as well as tests that exaggerate subtle neurologic deficits, such as walking with the head elevated, backing and turning in tight circles (Reed 2003; Furr and Reed 2015). In most cases of musculoskeletal causes of poor performance and rideability issues, blood work will provide ambiguous results, except for cases of recurrent exertional rhabdomyolysis which can be verified by abnormally high concentration of serum aspartate aminotransferase (AST) and increased creatine kinase (CK) after exercise compared with before exercise (Martin et al. 2000; Dyson 2010a, 2016b; Valberg 2018). As mentioned earlier, oral pain can also be a significant


cause of poor performance and behavioural changes in © 2020 EVJ Ltd


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