Species: Horse (Shetland pony), 11 years old, mare. Severe weakness and death within 24 hours.
Striking elevation of creatine kinase and gamma-glutamyl transferase. At necropsy, numerous skeletal muscles and cardiac muscle appeared pale with some haemorrhages. Two other ponies died in the same stable within the last two weeks.
Organ: Striated muscle (diaphragm).
Description: There are segmental and extensive degenerative and necrotizing changes in most of the striated myofibers (swelling, hypereosinophilia, vacuolation, loss of striation and nucleus, fragmentation). Small to moderate numbers of neutrophils, lymphocytes and macrophages surround these necrotic myofibers, which are multifocally invaded by macrophages. Satellite cells are activated. The interstitium is expanded by edema.
Morphologic diagnosis: Striated muscle: Acute multifocal extensive monophasic segmental muscle degeneration and necrosis.
Comments: Such lesions are non-specific due to the limited repertoire of striated muscle responses. Several hypotheses in this species could be therefore proposed such as: atypical myopathy, ionophore toxicosis, and vitamin E or selenium deficiency. Given these hypotheses, food has been evaluated: only poor-quality hay was given to the ponies that were in stalls at this season (winter). MCPA-carnitine in serum was tested on another pony still alive with similar clinical sign and the test was negative. Vitamin E concentration in serum was well above the baseline level. However, selenium concentration in serum was three times lower than the baseline level.
Authorship (text and photos): Christelle Villemonte Volmer (DVM, DESV-AP, Dipl ECVP, EBVS® European Specialist in Veterinary Pathology) and Charlotte Boyer DVM, DESV-AP, Dipl ECVP, EBVS® European Specialist in Veterinary Pathology)
Vetodiag, 6 route du Robillard, 14170 Saint Pierre en Auge, France.
cvolmer@vetodiag.fr