How to: Differentiate the Causes of Equine Collapse

Collapse in the horse is rare but has significant impact. The potential causes of collapse are many (Fig 1), but most clinical cases fall into a few ‘common’ diagnoses. Obtaining a detailed history, clinical examination and use of further focused diagnostic tests and video evidence should pay dividends and in most cases allow you to hone down the most likely cause of collapse (Table 1). It is worth warning the owners at the outset that if the episode has only occurred once it may be very difficult to get a diagnosis.
Some questions to consider in your mind when trying to differentiate the causes:

Does the collapse as described by the owner sound like a ‘faint’ or a seizure or does the horse sound sleepy when they occur?
The 3 main categories of collapse (or near collapse) encountered in clinical practice are syncopal episodes (faint), seizures and sleep disorders (variously termed adult narcolepsy, recumbent sleep deprivation, inappropriate sleep and idiopathic hypersomnia). Ask the owner to describe the episode(s) in their own words and then ask focused questions: e.g did the horse fully fall to the ground; what went down first: forelimbs, hindlimbs or all 4 legs together. Avoid being too keen to base the diagnosis on the owner’s preconceptions or your own! Look for key features that are not consistent with a diagnosis as well as those that are consistent. [...]