Equine Neurological Dysfunction

Its a scene all too familiar to equestrians A small crowd has gathered at the rail all focused on a horse and rider trotting around the arena. Amidst scratching heads various opinions arise. 
I think its his right hind says the rider. 
Nope definitely right front replies the trainer. 
I think hes dragging the left hind toe offers another bystander. 
The horse in question certainly does not seem sound however the source of the issue remains enigmatic to all observers. The lameness seems inconsistent and no two steps taken by the horse seem alike. Sometimes there is a toedrag sometimes he trips and stumbles and every now and then it seems like he swings a leg out to the side on a turn.

What is going on?
The detection of subtle lamenesses can prove challenging to even the most experienced horsemen. Matters are further complicated when the gait abnormality is inconsistent or intermittent. In some of these cases efforts to find the source of pain are fruitless. In fact some of these mystery lamenesses are not true painrelated lamenesses at all they are caused by neurological dysfunction. Sometimes differentiating between true musculoskeletal pain and neurological disease can be tricky. A major clue that the neurological system could be involved is a random appearance to the gait abnormality. That is the abnormal step is different each time rather than a consistently shortened stride dragged toe or head nod which are more characteristic of a painrelated lameness. Other potential indicators of neurological disease are significant loss of muscle excessive stumbling a staggering or swaying gait sweating that only occurs in one area of skin and apparent weakness of one or more parts of the body. More severe neurological disease can manifest as a dull depressed mental state complete paralysis of various muscle groups an inability to rise or behavioural changes such as aggression or compulsive behaviour. 
Form and Function
To understand how injury or disease of the nervous system can result in the clinical signs observed in affected horses it is first necessary to have a basic understanding of the anatomy and function of the nervous system in the normal horse. The parts of the nervous system are divided into various categories which reflect their anatomic location in the body andor their purpose. The following is a brief overview of these classifications.
1 Central vs. Peripheral Nervous System The central nervous system CNS refers to the