Page 421 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

396 CHAPTER 1

VetBooks.ir 1.763 1.764

Fig. 1.763 Clostridial abscess following a
thrombophlebitis. The infection invaded the
surrounding muscles and fascia.

which presumably cause local necrosis and acti-
vate dormant spores in the muscle, may create a Fig. 1.764 Ultrasound scan of the mid-cervical
suitable environment for myonecrosis to occur. region of the horse shown in 1.763. Myonecrosis is
Contamination via the haematogenous route may characterised by loss of the normal echostructure,
also explain abscesses without an apparent wound. increased echogenicity of the muscle tissue (arrows)
The disease evolves as a poorly delineated cellulitis and a poorly delineated network of hypoechogenic
with severe, rapidly developing myonecrosis, abscess exudate (arrowheads).
formation and accumulation of gas. Severe systemic
disturbances occur as a result of the release of exo-
toxins causing fever, septic shock and death. pleuropneumonia, colic or colitis should be excluded.
Blood samples reflect the severe toxaemia, with an
Clinical presentation inflammatory response and mildly increased muscle
The disease presents with rapid-onset toxaemia enzyme activity. Hypovolaemia with increased hae-
manifest as depression, fever, tachypnoea, anorexia matocrit and protein concentration is indicative of
and lameness. This progresses to tremors, dyspnoea, toxic shock. In the subacute stage, hyperfibrinoge-
recumbency and death. Horses may be found dead. naemia and neutropenia will become more obvious.
Usually there is one affected muscle, which is hot Ultrasonography will reveal the myonecrosis and
and swollen, and the skin discoloured and thinned the presence of exudate (Fig. 1.764) and, potentially,
(Fig. 1.763). Crepitus may be palpable suggesting of gas (Fig. 1.765). There is usually very marked
the presence of subcutaneous emphysema. There oedema in and around the affected muscle(s). An
may be a previous wound, which may have a malo- ultrasound-guided aspirate/s from affected tissue
dourous discharge. can be evaluated directly and submitted for anaero-
bic bacterial culture.
Differential diagnosis
Colic; other causes of septic shock; other causes of Management
abscesses; exertional myopathies. Aggressive treatment is essential. Antibiotic treat-
ment, consisting of intravenous penicillin at high
Diagnosis doses and very frequently, is required (e.g. 44,000
The clinical signs of clostridial myonecrosis are IU/kg i/v q2–4 h). Surgical debridement and fenes-
fairly unique. Other causes of severe toxaemia such as tration to aerate the tissues is also necessary, making