Cushing's and Seizures?

Q.  I was wondering if, in addition to the various topics that you discussed as possible causes of equine seizures ("AAEP Answerline: Seizures" in the November 1999 issue of The Horse, online at, Cushing's syndrome is a contributing factor. My gelding has the start of it, and exhibited an episode of shaking, colic, then a seizure. Is this part of Cushing's?


A. Cushing's disease is caused by a tumor or hyperplasia of part of the pituitary gland. Sometimes the pituitary gland becomes enlarged, but often it is not physically enlarged, just producing larger amounts of hormones than usual. (A complete summary of Cushing's is online at

Seizures are rare in the horse, and adult horses especially have a high seizure threshold. Cushing's disease can cause seizures, but they are very rarely seen with this disease. It is hard to say for sure why some Cushing's horses have seizures, but it might be from associated liver disease (sometimes seen with Cushing's), hyperglycemia (high blood sugar, which is common in Cushing's), or from the pituitary gland becoming enlarged with the tumor and compressing other structures of the brain (as mentioned above, not normally seen with Cushing's). I have worked with a number of horses with Cushing's, and none had seizures.

Your horse sounds a bit unusual to me. If he has not had a laboratory diagnostic test for Cushing's, then I would recommend you get one. If he truly did have a seizure and that seizure is associated with Cushing's, then you need to get him on appropriate medication.

Not to question your interpretation--but since this seizure was associated with a colicky episode, perhaps it wasn't a true seizure. Or if it was a seizure, perhaps it was due to severe electrolyte or fluid disturbance associated with the colic. If so, then perhaps you'll never see anything like it again. Just to add to the list of possibilities (you see, vets like to make lists of all options, likely and unlikely, to leave no stone unturned), is there any chance your gelding has Impressive breeding and could have hyperkalemic periodic paralysis (HYPP)? Your description reminds me of HYPP in a lot of ways.

Another thought is this: If you suspect the horse is having more seizures when you are not around (e.g. you find him with lots of unusual scrapes, nicks, "mussed up" appearance, stall damage, etc.), set up a video surveillance system. It is always helpful for your veterinarian to be able to see what the horse is doing along with your verbal description in order to make an accurate diagnosis and properly treat the signs.

About the Author

Nancy Diehl, VMD, MS

Prior to attending veterinary school, Dr. Nancy Diehl completed a master’s degree in animal science while studying stallion sexual behavior. Later, she completed a residency in large animal internal medicine at the University of Pennsylvania’s New Bolton Center and worked in equine practices in Missouri and Pennsylvania. Diehl also spent six years on faculty at Penn State, where she taught equine science and behavior courses and advised graduate students completing equine behavior research. Additionally, Diehl has co-authored scientific papers on stallion behavior, early intensive handling of foals, and feral horse contraception. Currently she is a practicing veterinarian in central Pennsylvania.

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