Page 417 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

392 CHAPTER 1

VetBooks.ir 1.761 1.762

Fig. 1.761 Ultrasound scan of the ascending pectoral Fig. 1.762 Longitudinal ultrasound scan of the
muscle on the craniomedial aspect of the forelimb, distal part of the triceps muscle in the caudal upper
showing an area of diffuse decrease in echogenicity forelimb area of a horse presenting with acute,
and loss of normal muscle architecture (arrows). This sudden-onset lameness and pain on flexion of the
is indicative of a partial tear and granulation tissue elbow. There is a large, anechogenic haematoma at
reaction within the torn portion of muscle. the musculotendinous junction (junction between
the muscle belly and aponeurosis) (arrows). The
distal part of the muscle appears hypoechogenic
Prognosis and heterogeneous because of fibre retraction,
This depends on the extent, severity and chronicity cell infiltration and necrosis (arrowheads). This
of the specific muscle injury. It varies from good to appearance is typical of a complete muscle tear.
more guarded in chronic injuries secondary to other
problems or where subsequent fibrosis or atrophy
leads to a permanent mechanical lameness, such as ATYPICAL MYOPATHY
fibrotic myopathy.
Aetiology/pathophysiology
NON-EXERCISE-INDUCED MYOPATHIES Atypical myopathy (AM) is a severe myopathy with a
high mortality rate that affects horses at pasture. It is
While many muscle diseases are precipitated by associated with the ingestion of the toxin hypoglycin
exercise, there are a number of disorders that affect A, found in the seeds, leaves and seedlings of trees of
horses at rest. Establishing whether a horse has the genus Acer (maples). In the UK, Acer pseudoplata-
recently exercised prior to the onset of clinical signs nus (sycamore tree) is frequently implicated, while
is therefore important in narrowing down the list of in North America it is Acer negundo (box elder). The
differential diagnoses. toxin binds to flavin adenine dinucleotide (FAD)