Page 428 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.9 Muscle disorders of the horse 403

VetBooks.ir systemic inflammation. Diagnosis is based gener- Prognosis
The prognosis is generally fair, as long as the practi-
ally on clinical signs suggestive of a local abscess,
with or without a fistula being present, ultrasound
nent debilitation and disfigurement. Healing after
examination to identify areas of abscessation and tioner initiates treatment rapidly to prevent perma-
their extent, and guided fine-needle aspiration for drainage may be prolonged and there may be recur-
culture and sensitivity samples. Serology through rence or delayed healing, but the condition is rarely
a synergistic haemolysis inhibition test is useful for life threatening and usually leaves no significant
intra- abdominal or thoracic abscesses but has proved untoward effects. When musculoskeletal infection
unreliable for muscular abscesses. C. pseudotubercu- with C. pseudotuberculosis results in osteomyelitis or
losis infection of musculoskeletal structures should septic arthritis, prognosis for survival is poor.
be considered in horses with severe lameness and
an inflammatory leucogram during autumn/winter HYPOCALCAEMIA
months where it is prevalent.
Definition/overview
Management Hypocalcaemia per se relates to a decreased blood cal-
Unlike internal infection and ulcerative lymphan- cium concentration causing a stiff gait, weakness and
gitis, in musculoskeletal abscessation, the use of multiple muscle fasciculations (spasms). Conditions
antimicrobials is not recommended because this associated with hypocalcaemia include lactation in
may delay maturation of the abscess and prolong the the mare (‘eclampsia’ or ‘lactation tetany’), transport
disease course. Additionally, antimicrobials should or stress (‘transport or ‘stress’ tetany’), endurance
not be used in mature abscesses because of their exercise, acute kidney injury or severe metabolic dis-
low permeability across abscess membranes. The orders such as colic, enterocolitis or pleuropneumo-
abscess should be located, a hot poultice applied to nia. It can also be caused by intoxication with the
the affected area to stimulate abscess maturation, cantharid beetle, found especially in alfalfa hay, or
and then lanced and drained thoroughly under ultra- oxalate ingestion, and may be difficult to differenti-
sound guidance. Daily chlorhexidine flushes should ate from the ‘exhausted horse syndrome’ (see p. 404).
be performed to eliminate purulent exudate and bac-
teria. If antimicrobial treatment is required, such as Aetiology/pathophysiology
if multiple sites are affected or there is concurrent Extracellular calcium concentrations affect the volt-
lymphangitis, an antimicrobial with intracellular age at which sodium channels are activated; calcium
penetration, improved activity in the presence of ions act as a sodium channel antagonist by decreased
exudates and culture and sensitivity results should sodium permeability and increasing the depolari-
be recommended. NSAIDs are used for their anal- sation threshold. Therefore, a decrease in calcium
gesic properties. concentration leads to hyperactivity of the sodium
channels and muscle fasciculations, tremors, tetany
Prevention and seizures. Tachycardia and cardiac arrhthymias
Controlling the fly population is crucial to prevent may also be present. As calcium and magnesium
and control infection. C. pseudotuberculosis is able to homeostasis are linked, it is not unusual for horses
survive for months in soil, hay, fencing and fomi- with hypocalcaemia to also have low magnesium
tes and, therefore, when abscesses are lanced and concentrations.
flushed, it is imperative to collect and properly dis- Hypocalcaemia may cause sustained skeletal
pose of the exudate to minimise exposure to both muscle contractions or tetany. Any horse with severe
other horses and man. A vaccine against C. pseu- hypocalcaemia can develop tetany, although it is
dotuberculosis was briefly available in 2016, but was more frequent in lactating mares and horses trans-
quickly removed from the market due to adverse ported for long distances, especially in hot weather.
effects. A second generation of the vaccine may be The recruitment of calcium in the milk of the mare
released in the future. at the peak of lactation (around 60–100 days post