Concurrent atypical myopathy and equine dysautonomia in two horses

Abstract

This report concerns 2 horses that suffered typical clinical signs of atypical myopathy (AM) and equine grass sickness (EGS) concurrently. Clinical details and pathological lesions of the cases are described. EGS and AM are relatively rare diseases and the concurrency of the diseases in the same animals is therefore considered unlikely to be a coincidence. However, it is not suggested that the evidence shows a common aetiology but rather the existence of common predisposing causes.

Concurrent conditions in single cases: The need to differentiate equine dysautonomia (grass sickness) and atypical myopathy

“…In horses acutely critically ill at pasture, a tentative diagnosis of AM is strongly suggested by the concomitance with an AM outbreak. Both cases described in the report of Vercauteren et al (2007) occurred during the large European outbreak observed in autumn 2006 (Anon 2007). Further key elements in these 2 cases that reinforce a tentative diagnosis of AM were their young age, the sudden recumbency and a history of permanently living at pasture without supplementary feeding.…”

“…As frequently found in AM, a paralysed, distended urinary bladder was evident on rectal palpation in one of the 2 cases with both EGS and AM, and in the one of the cases dysphagia was accompanied by oesophageal obstruction: the latter has been noted in more than 30% of AM cases ). Based on the history, and clinical and histological findings of the 2 cases reported by Vercauteren et al (2007), there is no doubt that both horses suffered from AM.…”

“…A 'toxin' is suspected in both conditions; however, the aetiology remains unidentified. As proposed by Vercauteren et al (2007), common epidemiological risk factors may account for the occurrence of both conditions in these 2 unfortunate animals, even if the individual diseases have a low incidence. Alternatively, the shared epidemiological features of EGS and AM, along with the recognition of lesions of both diseases in the same horses, could reasonably suggest the hypothesis that EGS and AM represent opposite extremes of a more generalised process.…”

“…Lesions consist of striking neuronal chromatolysis, most consistently noted in the visceral lower motor neurons (LMN) CN III and X and the somatic LMN of CN III, V, VII and XII. In this issue (pp 463-465), Vercauteren et al (2007) briefly noted that brainstem chromatolytic neurons were indeed present in their 2 cases with lesions of both EGS and AM, and it would be interesting to ascertain their precise anatomical locations.…”

“…The report by Vercauteren et al (2007) in this issue should, however, act as an impetus to carry out further detailed neuropathological investigation of AM cases, focusing particularly on the autonomic ganglia and central nervous system. = common or typical with this condition; () = infrequent but possible with this condition; = not a feature of this condition; 0 = typically not used to confirm or rule-out this condition; CK = creatinine kinase.…”