Impact of Different Diagnostic Procedures on Diagnosis, Therapy, and Outcome in Horses with Headshaking: Recommendations for Fast-Track Advanced Diagnostic and Therapeutic Protocols

SIMPLE SUMMARY: The major cause of headshaking in horses is idiopathic trigeminal-mediated headshaking, which often has a guarded long-term prognosis. Thus far, it is diagnosed by the exclusion of other differentials. Therefore, in most horses presented with headshaking, a considerable number of diagnostic procedures and different therapies are performed. The objectives of this study were to analyse the impact of different diagnostic procedures on diagnosis, therapy, and outcome in horses with headshaking and to establish recommendations for fast-track advanced diagnostic and therapeutic protocols. An underlying pathology causing the headshaking signs was identified in 6% of the studied horses. After the exclusion of differentials via history and clinical signs, most of the clinically relevant findings were detected with computed tomography, and causality was proven through positive local anaesthesia or targeted therapy. Thus, the number of diagnostic procedures can be significantly reduced. All the horses with underlying conditions demonstrated a positive outcome. In conclusion, the clinical relevance of diagnostic findings should be verified through local anaesthesia or targeted therapy, depending on the invasiveness of procedures, risks, and expected benefits. Furthermore, thorough patient history, clinical signs, and computed tomography turned out to be most beneficial and should be considered as core components in a short diagnostic protocol. ABSTRACT: Most horses affected by headshaking (HS) are diagnosed with idiopathic trigeminal-mediated headshaking (i-TMHS) when no underlying disease is found. Diagnosis is made by the exclusion of differentials considering history, clinical signs, and diagnostic investigations. Therefore, in horses presented with headshaking, many diagnostic procedures and therapies are conducted. Retrospectively, the digital patient records of 240 horses with HS were analysed regarding the impact of diagnostic procedures on diagnosis, therapy, and outcome. Horses were extensively examined using a standardised protocol including clinical (ophthalmologic, orthopaedic, neurologic, dental) examination, blood analysis, and imaging techniques (endoscopy, radiographs, computed tomography (CT), and magnetic resonance imaging). Many findings were revealed but were of clinical relevance in only 6% of the horses. These horses were, therefore, diagnosed with secondary headshaking (s-HS). In addition, all of these horses demonstrated a positive outcome. The CT of the head revealed 9/10 of the clinically relevant findings. Other diagnostic procedures had no major additional impact. Conclusively, the diagnostic investigation of horses with HS should aim at differentiating i-TMHS from s-HS. The clinical relevance of findings should be verified through diagnostic anaesthesia or targeted therapy depending on risks, invasiveness, and expected benefits. To reduce the multitude of examinations, diagnostic investigations should focus on the CT of the head in those horses with suspicion of i-TMHS based on typical history, clinical signs, and physical examination.