There is a predominance of level 4 evidence evaluating surgical treatment of RLN.Many studies do not stand up well to rigorous methodological evaluation.Whilst randomisation of treatments and inclusion of an appropriate control population is extremely difficult in clinical equine studies, there are several other simple ways in which the evidence base could be significantly improved.Despite a large numberof papers having been published on treatments for recurrent laryngeal neuropathy, the critical evidence base to support these treatments is weak, consisting mainly of low level clinical evidence. When considering 'levels of evidence' (Figure 1), systematic reviews of multiple studies are considered the highest level of evidence (level la) followed by well conducted randomised controlled studies (RCTs, level lb). Unfortunately, RCTs have been avoided in equine veterinary surgery because of methodological, financial and ethical constraints, and unsurprisingly, there is only one RCT published in the field of RLN surgery, which was performed in horses with experimentally induced RLN. Cohort studies represent level 2 in the clinical evidence 'pyramid', followed by case-control studies at level 3, case series and case reports at level 4 and expert opinion representing the lowest level of evidence at level 5.
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