Understanding Stringhalt (Equine Reflex Hypertonia)

 associated plants is found in pastures or hay. X-rays and/or ultrasound may be required to rule out injuries to the muscles, tendons, or hocks of the hindlimbs. Additional diagnostic tests may be utilized to rule out muscle diseases such as polysaccharide storage myopathy (PSSM) and infectious diseases such as equine protozoal myeloencephalitis (EPM). Gait analysis may be performed to distinguish stringhalt from shivers (Draper et al. 2014. Equine Vet J 47(2): 175-181).

Treatment

There is no definitive treatment for stringhalt. Some horses may recover spontaneously. In cases of plant poisoning or intoxication, horses should be removed from areas containing the toxic plant. Surgical resection of part of the muscle and tendon (myotenectomy) of the lateral digital extensor at the level of the hock may alleviate signs of chronic stringhalt, but the success rate is variable. Administration of muscle relaxants, anticonvulsants (phenytoin), tranquilizers (acepromazine), and other medications can be helpful in some cases, but the effects are often temporary. One study reported fewer stringhalt-like steps after repeated injections of Botox (Wijnberg et al. 2009. Equine Vet J 41:313-318).

Prognosis 

The prognosis for horses with stringhalt varies depending on a number of factors. Horses may not return to performance, but they can still have a good quality of life. Some horses respond to treatment, whereas others do not. Most horses with acquired stringhalt improve within days, but recovery can take months or years in some cases. Relapses may occur, but even severely affected horses may return to normal. Idiopathic stringhalt is usually irreversible without surgery.