I’ve been around long enough to see this happen several different times. A new condition receives a lot of press and the next thing you know it is blamed for a wide range of complaints with little or no justification.
Opossums spread the organism which causes EPM, Equine Protozoal Myeloencephalitis.
EPM, first described in 1964, was a disease du jour for many years and to some extent still is today. Many horses that were actually lame or just plain poor movers/badly gaited were suspected of EPM. The stiff movement, reluctance to move and muscle trembling of horses with laminitis pain has been misdiagnosed as EPM. Even sensitivity to touch has been blamed on EPM.
Although it is difficult to confirm diagnosis by blood work because only about 1% of horses with antibodies will ever actually have symptoms, there are specific things to look for with EPM. A careful exam will reveal abnormalities that are clearly neurological not lameness. There is almost always asymmetrical muscle loss. Horses that truly have EPM and are not treated will continue to show signs and worsen.
EPSM, Equine Polysaccharide Storage Myopathy, is another probably overdiagnosed disease. There are many causes of tying up other than EPSM. Diagnosis can only be made by muscle biopsy, or genetic testing for one form of the disease. Despite this, many horses are assumed to have EPSM even without obvious tying up. Back pain, reluctance to back, poor attitude toward work, poor movement, even bad behavior for the farrier often get a label of EPSM.
Most recently, gastric ulcers holds the title of disease du jour. Multiple studies have shown that if you randomly examine any horse the odds are better you will find ulcers than you will not. Even asymptomatic, unstressed mares at pasture showed 60% with ulcers in one study and up to 57% of foals up to the age of 3 months develop gastric ulcers but with a much lower percentage actually having any symptoms. Spontaneous healing is the norm with foals.
In short, there is no inevitable connection between gastric ulcers and the presence of symptoms. A clear connection between the presence of ulcers and athletic performance such as racing has also not been established. Bruxism (tooth grinding) and interrupted feeding are the most common when there are symptoms, with colic in more severe cases.
Signs such as behavioral changes, resistance to aids, reluctance to go to the right, muscle/back pain, chiropractic issues, sensitivity to girth tightening etc. are not specific for ulcers. They may indeed be related to the horse having pain somewhere, just not specifically ulcers.
The danger of buying into the disease du jour is the potential for a lot of wasted time and money. A host of supplements and alternative treatments always pop up to address these popular diagnoses. You are much better off getting a definitive diagnosis in the first place.
Eleanor Kellon, VMD