SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
to determine if they would have given better performances or won in better classes if
they had not had such raised activities.
Plasma/serum Muscle Enzyme Activities in Rhabdomyolysis
Increases in total plasma/serum CK and AST activities in equine rhabdomyolysis
were first reported in the 1960's. It has been suggested that, although AST activities
would increase slightly with mild muscle inflammation and liver disease, much higher
values were likely to be found in acute equine rhabdomyolysis.
The time at which peak circulating activities of these enzymes may be found,
following an attack of equine rhabdomyolysis, has been reported as 3-15 hours for
CK and at least 24 hours for LDH and AST. The time to return to the pre-attack
activities has been given as 1-7 days for CK; 5-10 days for LDH and 2-4 weeks for
AST depending on the extent of the initial increase. These differences allow the
simultaneously measured AST and CK activities to be used to indicate whether the
muscular damage is active or resolving. The rise in enzyme activities may be
proportional to the degree of muscle fiber damage as well as the clinical severity.
However, some cases of mild clinical severity have been found to have markedly
higher CK and AST activities than cases showing signs typical of more marked
clinical severity. A partial explanation may be that animals have different pain
thresholds and the nature or temperament of the horse may be important. Damage
to certain muscle groups may also be more painful than damage to others. Another
possibility is that some animals suffer a mild but generalized pathological increase in
cell permeability which results in a marked increase in plasma muscle enzyme
activities but little overt muscular damage and pain.
Using muscle enzyme activities alone to make a diagnosis of equine rhabdomyolysis
has been questioned. Problems with diagnosis can arise when either elevated
plasma enzyme activities without clinical signs, or clinical signs without increased
activities, are found. Mild clinical signs can be missed and it is possible that a more
detailed examination of the stride length and limb positioning of those animals with
high activities and no clinical signs, may reveal abnormalities not obviously apparent.
Several apparently healthy endurance horses have been reported to have elevated
resting plasma enzyme activities. Following endurance rides high CK activities have
been found in some animals, which return towards baseline values within 24 hours,
without any clinical signs of muscular damage. The increase in CK in these cases
could not be correlated with poor performance or post-exercise signs of fatigue.
These elevated levels possibly reflect an altered state of muscle metabolism caused
by the endurance exercise. Such changes appear to be confined to individuals and
do not appear to be a general finding. This suggests that the physiological or
pathological processes involved are unique to the individual(s) rather than being
linked to endurance riding alone.
67