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Background: Equine grass sickness (EGS) is a frequently fatal multisystem neuropathy of equids. The aetiology is unknown; proposed causes include toxicoinfection with Clostridium botulinum and a mycotoxicosis. The effect of EGS on the organisation and structural integrity of the skeletal neuromuscular junction (NMJ), the target of botulinum neurotoxins (BoNTs), is unknown. Objectives: To compare the organisation and structural integrity of skeletal NMJs from EGS horses, control horses and one horse with a presumptive diagnosis of botulism. Study design: Blinded, retrospective case control. Methods: NMJs in samples of diaphragm or intercostal muscle from six EGS horses, three control horses and one equine botulism case were compared using electron microscopy, morphometry and confocal light microscopy. Results: A significantly higher percentage of EGS NMJs had abnormal morphology (EGS 72.2%, 95% CI 55.6–84.4; Controls 6.9%, 1.7–23.8; OR 35.1, 8.47–244.8; p < 0.001). EGS NMJs had a significantly lower mean volume fraction occupied by synaptic vesicles (SVs) (EGS 18.7%, 12.6–28.0; Controls 36.3%, 20.8–63.4; p = 0.024). EGS NMJs had evidence of accelerated SV exocytosis and SV depletion, accumulation of neurofilament‐like material in terminal boutons and/or bouton degeneration. NMJs from the botulism horse had dense packing of SVs towards the presynaptic membrane active zone, consistent with BoNT intoxication, but had absence of the abnormalities identified in EGS NMJs. Main limitations: Group sizes were limited by difficulties obtaining suitably processed samples. Ages of control and EGS horses differed. Botulism was diagnosed based on clinical and post mortem findings. Conclusions: EGS is associated with major changes in skeletal NMJ ultrastructure that are inconsistent with the effects of BoNTs. SV depletion may reflect increased exocytosis coupled with reduced repopulation of SVs via anterograde axonal transport and endocytosis, consistent with the action of an excitatory presynaptic toxin and/or neurotransmitter reuptake inhibitor. Skeletal NMJs represent a previously unrecognised target for the toxin that causes EGS. [ABSTRACT FROM AUTHOR]

Background: Fractures of the paracondylar process of the occipital bone may cause headshaking, neck pain and neurologic deficits. The condition is being recognised more frequently with increasing availability of computed tomography. However, to date only limited information is available as to presentation, treatment, surgical approach and outcome. Objectives: To describe the clinical signs, imaging findings, treatment, surgical approach and outcome in three horses diagnosed with paracondylar process fracture. Study design: Retrospective case series. Methods: Clinical records and diagnostic images of affected cases were reviewed. Results: Two cases had ventral nonunion fractures—one of these presented with neck pain, headshaking and behavioural changes, while in the other the fracture was a suspected incidental finding in a case of poor performance. A third case with a more dorsal fracture presented with acute facial nerve paralysis. Diagnosis was by computed tomography in all cases, although imaging of ventral fractures by radiography was found to be feasible. Where clinical signs could be associated confidently with the fracture, conservative management resulted in improvement but not complete resolution. Repeated recurrence of clinical signs after prolonged periods of remission necessitated surgical removal in one case, which was readily accomplished with the aid of ultrasound guidance, and led to rapid resolution of clinical signs without significant post‐operative complications. The surgical approach is described. Main limitations: Limited follow‐up was available. Conclusions: Paracondylar process fracture should be considered as a differential diagnosis for headshaking, neck pain, poor performance and facial paresis, and is a justification for performing computed tomography in such cases. A multi‐disciplinary approach is beneficial due to the potential for orthopaedic, neurologic, ophthalmologic and behavioural clinical signs, with additional need for expertise in diagnostic imaging and pain management. Surgical fragment removal should be considered for ventral fractures. [ABSTRACT FROM AUTHOR]

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