Page 425 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

400 CHAPTER 1

VetBooks.ir around 4–8 hours after the end of anaesthesia (CK also be due to external trauma from ropes, kicks or
falls or secondary to a wound, intramuscular injec-
is often increased 100- or 1000-fold). There may
be hyperkalaemia, hypocalcaemia and acidosis with
early hyperlactacidaemia. There may be signs of tion or surgical trauma. There may initially be a hae-
matoma, but chronic strain on the healing wound
renal failure (increased urea and creatinine concen- leads to muscle atrophy and the formation of exuber-
trations) and other vascular imbalances. Urine anal- ant fibrous tissue within the muscle, most commonly
ysis reveals myoglobinuria and presence of blood. at the muscle/tendon junction. Recurrent inflam-
mation may lead to osseous or fibocartilaginous
Management metaplasia with associated mineralisation (ossifying
Intravenous fluid therapy and NSAIDs are the myopathy). A congenital form has been described in
mainstay of treatment. Opioids can used in particu- yearlings, supposedly through perinatal trauma.
larly painful cases. Clinical signs usually improve
rapidly if the animal is standing and therefore a hoist Clinical presentation
and harness may be used if the horse’s temperament In the acute form there may be an acute lameness
allow this. Palliative and supportive therapies to with focal swelling over the caudal aspect of the
limit muscle damage from recumbency include pro- thigh. In most cases the condition is encountered
vision of adequate padding, maintenance in sternal in the chronic stage. The characteristic mechani-
recumbency and regular turning over. cal gait abnormality includes slapping of the hoof to
Dantrolene sodium has been used in the ground following protraction of the hindlimb,
Thoroughbreds with a history of RER that develop resulting in a reduced cranial phase of the stride.
myopathy following anaesthesia. This is due to restriction of the cranial phase by a
functional shortening (or lack of stretching) of the
Prognosis caudal thigh muscles. The condition is usually uni-
Variable depending on the severity and extent of lateral, although bilateral cases have been recorded
the muscle damage, and on the animal’s tempera- secondary to external trauma to the caudal aspect of
ment. If the horse is able to stand, the prognosis is both hindlimbs during transporting.
good. Recovery may take a few hours to several days.
Prolonged recumbency leads to a poor prognosis. Differential diagnosis
The gait should be differentiated from other ortho-
FIBROTIC/OSSIFYING MYOPATHY paedic injuries or neuromuscular disorders affecting
the hindlimbs, such as stringhalt and shivering, and
Definition/overview ataxic neurological cases.
This is an uncommon condition characterised by a
severe muscle tear and subsequent formation of fibrous Diagnosis
scar tissue (fibrotic myopathy) that may become min- The diagnosis is usually made on the basis of his-
eralised (ossifying myopathy). This leads to a charac- tory, clinical findings and the characteristic features
teristic mechanical, non-painful gait abnormality. It of the gait abnormality. The abnormality is most
is encountered in Quarter horses and barrel racers obvious at the walk. The abnormal area of damaged
and, rarely, in other breeds. It primarily affects the muscle is usually palpable. There is no improve-
semitendinosus muscle and, less commonly, the semi- ment in the gait following regional or intrasyno-
membranosus, biceps femoris and adductor muscles. vial analgesia techniques. Ultrasonography is the
diagnostic method of choice as it will confirm the
Aetiology/pathophysiology presence of an echogenic or hyperechogenic lesion
Fibrotic and ossifying myopathy may occur due at the muscle/tendon junction (Figs. 1.769, 1.770).
to spontaneous trauma (muscle strain), probably Mineralisation may be visualised and the extent of
through repeated overstretching of the muscle in the lesion (i.e. which muscle/s are involved) can be
association with rapid pivoting actions around the determined. This is particularly useful if surgery is
hind feet and sudden stop and slide actions. It may to be considered.