Page 1119 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1094 CHAPTER 10

VetBooks.ir Sciatic of approximately 50%. Complications of prolonged
recumbency (ischaemic neuropathy, decubital ulcers)
The sciatic nerve has a close relationship with the
pelvis and may be damaged by pelvic fractures,
especially ischial fractures. In foals, deep injection frequently necessitate euthanasia.
reactions caudal to the proximal femur and osteomy- Management
elitis of the sacrum and pelvis have resulted in sci- Medical management of peripheral nerve injuries
atic paralysis. Treatment of primary problems may involves reduction of inflammation, relief of muscu-
resolve the sciatic paralysis, but if the nerve is severed loskeletal pain, prevention of secondary medical dis-
the prognosis is poor even with surgical anastomo- orders and provision of adequate nutrition. Systemic
sis, because there is a great distance over which fibre administration of dexamethasone (0.05–0.20 mg/kg
regeneration must occur. Sciatic palsy can also occur i/v q12 h), flunixin meglumine (1.1 mg/kg i/v q24 h)
with spinal cord lesions affecting the L5–S3 ventral or phenylbutazone (2.2 mg/kg p/o q12 h) for 3 days
grey matter or nerve roots. Other signs such as uri- may help suppress local inflammation that can fur-
nary bladder paralysis, gluteal atrophy and exten- ther damage nerve fibres. Confinement in deeply
sor weakness may also be present. The sciatic nerve bedded stalls is appropriate and application of cold
supplies the main extensor muscles of the hip and water or ice packs in the first 24 hours may be ben-
flexor muscles of the stifle and divides into peroneal eficial. Recumbent animals should be turned 6–8
and tibial branches. Total sciatic paralysis results times daily to prevent decubital ulcers and pressure
in an abnormal gait and posture. At rest, extension myopathy. Support of some patients in slings may be
of the stifle and hock results in the limb hanging useful and helps maintain strength in the opposite
behind the horse with the fetlock and interphalan- limbs.
geal joints partly flexed and the dorsum of the hoof
on the ground. If the foot is manually advanced and TOXIN-ASSOCIATED DISORDERS
placed on the ground ventral to the pelvis, the horse
can support weight with some flexion of the hock BOTULISM
and take a stride. Muscles of the caudal thigh and
the entire limb distal to the stifle atrophy. Degrees Definition/overview
of hypalgesia over most of the limb, except for the Botulism is a rapidly progressive neuromuscular dis-
medial thigh, have been reported. ease that is often fatal in horses. It is caused by toxins
produced by Clostridium botulinum, which is a gram-
Post-foaling paralysis positive spore-forming anaerobic bacterium found
The obturator nerve innervates the adductors of the in animals, birds, soil and organic material. Horses
thigh and paralysis is an infrequent sequela to foal- are one of the most susceptible species, with both
ing. Signs may be seen without a history of dysto- individual and group outbreaks reported.
cia. This nerve courses along the medial aspect of
the shaft of the ilium and is vulnerable to compres- Aetiology/pathophysiology
sion by the foal impinging on this region during Eight botulinum neurotoxins (BoNTs) are produced
parturition. Depending on the severity of damage, by different strains of C. botulinum. The geographi-
signs may range from mild stiffness to paraplegia. cal distribution of BoNT types varies, and the clini-
Unilateral damage may be apparent as abduction cal presentation of each type may be subtly different.
and circumduction of the affected limb at the walk. There are three pathogenic mechanisms of botu-
Bilaterally affected animals have great difficulty ris- lism in the horse:
ing and may require the support of a body sling.
Haemorrhage in and around the femoral nerves • Adult botulism: ingestion of pre-formed
has also been associated with foaling and results in toxin. In Europe, the most common form of
extensor weakness. The prognosis for survival in botulism is caused by the ingestion of forage
post-foaling paralysis is fair, with a recovery rate contaminated with BoNT from animal