Page 1101 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1076 CHAPTER 10

VetBooks.ir 10.26 10.27

Fig. 10.26 Prolapse of the nictitating membrane in a Fig. 10.27 ‘Saw-horse’ muscle rigidity noted in a
horse with tetanus. horse with tetanus.

the horse to fall in response to external stimulation, because low concentrations of the organisms may be
and fractures of the pelvis, skull, femur, tibia and present in the wound, and because strict anaerobic
radius have been reported. Some severe cases may conditions are required for culture. Gram staining of
develop apparent seizures. an aspirate from the wound is of limited diagnostic
Horses that survive usually begin to show signs value, because the sporulated and vegetative forms
of improvement within 10–14 days, but clinical signs of the organism appear similar to other anaerobic
may persist for weeks to months. Of 56 working bacteria. There are no characteristic post-mortem
equids treated in one hospital, 46% survived, and the lesions associated with tetanus.
majority were returned to their owners with few or
no residual clinical signs. Differential diagnosis
Given the challenge in making an ante-mortem
Diagnosis diagnosis of tetanus, it is important to rule out dif-
A presumptive diagnosis of tetanus is based on ferential diagnoses in the horse, through various
history, clinical signs and response to treatment. means. A list of differential diagnoses, and their
A definitive diagnosis of tetanus is challenging; means of differentiation from tetanus in the horse,
microbiological culture of the organism may fail are summarised in Table 10.6.

Table 10.6 Differential diagnosis for tetanus for horses in Europe
DIFFERENTIAL DIAGNOSIS (SIMILAR PRESENTING SIGNS) DIAGNOSIS
Laminitis (stiffness) Pounding digital pulses; lateral distal phalanx radiographs
Meningitis (stiffness) Cerebrospinal fluid cytology
Myopathies (stiffness) (e.g. polysaccharide storage myopathy, Serum muscle enzyme concentrations, plasma fibrinogen and
immune-mediated myositis, nutritional myopathy, exertional serum amyloid A
myopathy)
Cervical vertebral fracture/pain Cervical radiographs
Equine motor neuron disease (muscle fasciculations, reluctance Retinal lesions, muscle biopsy (sacrocaudalis dorsalis medialis)
to move, dysphagia)
Hyperkalaemic periodic paralysis (stiffness, muscle Episodic, often associated with hyperkalaemia, Appaloosa/Quarter
fasciculations) horse, ‘Impressive’ genetic lineage; DNA testing available