Page 45 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

20 CHAPTER 1

VetBooks.ir Lactate dehydrogenase substance p); growth factors (high mobility group B
[HMGB]-1); and certain matrix enzymes (matrix
Lactate dehydrogenase (LDH) is found in many
organs as well as in skeletal muscle. Elevations are
seen in rhabdomyolysis. As with AST, LDH should metalloproteinases [MMPs], ADAMTS serine
proteases).
be measured with CPK. Although this is a fast moving research topic and
there has been good evidence supporting the use-
Exercise test fulness of indirect biomarkers in the prevention and
The measurement of CPK, AST and LDH at management of equine joint disease, the reality is,
rest, 6 hours and 24 hours after exercise can be however, that day to day use still remains mostly
useful as an aid to diagnosing chronic exertional limited to clinical research studies or large equine
rhabdomyolysis. A >4-fold increase on the first centres that have a strong associated research lab-
sample or persistently elevated levels of the three oratory working in this field. This is very likely to
enzymes over the test period may indicate muscle change in the near future.
damage.
Tendon sheath markers for tendon pathology
Joint markers for osteoarthritis Most of the work on tendon biomarkers has used
Biomarkers are parameters that are objectively in-vitro models. COMP, cyclooxygenase (COX)-2,
measured and evaluated as indicators of a certain IL-6 and MMP-13 have been shown to be increased
biological process, be it physiological or patho- in cultured tendon cells and explants when stressed.
logical. As the onset of clinical signs of joint pain Since these are not tendon specific, RNA sequenc-
(lameness) usually appear well after the onset of ing has recently identified new markers of tendon
disease, intensive research interest has been given disease, such as EYA2 and GPRIN3, and specific
to identifying biomarkers of joint disease that could tendon markers of normal tendon. Similar to joint
provide more accurate and early diagnosis as well disease, the clinical usefulness of these remains lim-
as monitor disease progression. Biomarkers are ited at present.
commonly divided into two main categories: direct
and indirect. Direct biomarkers are those related Serology
to tissue metabolism or destruction, and indirect High antibody titres to the tick-borne organism
markers are molecules produced due to the inflam- Borrelia burgdorferi may be seen in Lyme disease.
matory or disease process but are not a product of Measurement of Brucella titres may be useful in the
cell or matrix breakdown. diagnosis of fistulous withers, vertebral osteomyeli-
tis or unexplained neck pain.
Direct biomarkers Some of the direct biomarkers that
have received most interest are: carboxypropeptides of Muscle biopsy
type II collagen (CPII); epitopes of chondroitin sul- Muscle biopsy can be useful for diagnosing specific
phate; glycosaminoglycan keratan sulphate; cartilage muscle disorders such as polysaccharide storage
oligomeric matrix protein (COMP); and biomarkers myopathy (PSSM) and nutritional myodegeneration
of bone metabolism such as osteocalcin (OC), bone- (NMD). Biopsy of the sacrocaudalis dorsalis muscle
specific alkaline phosphatase (BAP) and type I collagen is also used for confirmation of equine motor neuron
C telopeptides (CTXs). disease (EMND). The sample may be obtained under
sedation and local anaesthesia via a small, vertical skin
Indirect markers Many molecules have been iden- incision over the muscle of interest by either using
tified as useful markers of joint disease, but the main a 6 mm skin percutaneous biopsy needle or surgi-
ones are: cytokines (interleukin [IL]-1, tumour cally excising a 2 cm cube of muscle (Fig. 1.43). The
necrosis factor [TNF]-α and IL-6); inflammatory skin is routinely closed with non-absorbable suture
and pain mediators (prostaglandin [PG]E2 and material. Routine histopathological biopsy samples