Muscle: biopsy in Horses (Equis) | Vetlexicon
equis - Articles

Muscle: biopsy

ISSN 2398-2977

Contributor(s) :


Podcast: Muscle: biopsy

Introduction

  • Muscle biopsy is an under utilized technique that can provide valuable information about the etiology of neuromuscular conditions.
  • It would be primarily used in the investigation of recurrent or rhabdomyolysis   Muscle: myopathy - exertional rhabdomyolysis  and muscle wasting associated with neuromuscular disease, particularly suspected EMND   Neurology: motor neuron disease  .
  • While typically used for generalized muscle disorders, it is also useful for localized muscle disorders, eg myositis.

Indications

  • Recurrent rhabdomyolysis   Muscle: myopathy - exertional rhabdomyolysis  .
  • Shivering.
  • Hindlimb weakness.
  • Hindlimb muscle atrophy   Hindlimb: muscle atrophy 01    Hindlimb: muscle atrophy 02  .
  • Generalized weakness and atrophy.
  • Local muscle swelling, pain or atrophy of unknown etiology.

techniques for recurrent rhabdomyolysis

Needle biopsy

  • Either muscle group can be sampled using a muscle biopsy needle. These are modified Bergstrom Angstrom needles with a diameter of 5 mm   Muscle: biopsy needles  .
  • Advantages:
    • Minimally invasive with no suturing required and no time off work required.
  • Disadvantages:
    • It does require some experience to take appropriate samples and while the needles are re-useable, they are expensive to purchase.
    • Sample size is also small, and usually required some experience to get the most out of the sample obtained.

technique

  • Clip and surgically prepare a small area (10 x 10 cm) on the rump a hand's breadth from the tuber coxae in an adult horse   Muscle: needle biopsy 01  .
  • Instill 3 ml of local anesthetic subcutaneously and just below the fascia, taking care not to instill it into the muscle itself.
  • Using a No 10 scalpel blade, make a stab incision through the skin and fascia.
  • Wearing sterile gloves, take the center piece from the needle and place on a sterile tray. Hold the needle (outer piece and cutting piece together) with the window facing away from you. Insert the needle to a depth of 8 cm into the middle gluteal muscle, pull out the cutting piece so as to open the window, tilt upwards (away from you) slightly to allow the muscle to bulge into to window and make 4 to 5 cuts using the cutting piece   Muscle: needle biopsy 02  .
  • Withdraw both pieces together and use the center piece to remove the muscle sample from the cutting piece   Muscle: needle biopsy 03  .
  • Tease out aligned fibers and fix using 10% buffered formalin or freeze using a recognized technique.

Surgical biopsy

  • The semimebranosus/semitendinosus muscles are useful for surgical biopsy techniques.
  • Advantages:
    • Is easily performed and producing a large sample size.
    • Analysis of greater numbers of fibers may increase the chances of finding equine polysaccharide storage myopathy (EPSM).
  • Disadvantages:
    • The technique does require suturing and a short period of convalescence.

technique

  • Clip and surgically prepare an area of approximately 30 cm length and 20 cm width either just above or below the tuber ischii, approximately 5 cm lateral to the tail.
  • Make a subcutaneous "L" block using local anesthetic so as to avoid infiltration of local anesthetic into the area where the sample will be taken from.
  • Make a 10 cm long incision in a vertical plane over the muscle.
  • Using curved hemostats, bluntly dissect and elevate a 1 cm diameter by 3 cm long piece of muscle aligned in the same plane as your incision   Muscle: surgical biopsy 01  .
  • Using a scalpel, incise one end of the elevated muscle, then, gently holding the free end, cut the fixed end also   Muscle: surgical biopsy 02  .
  • Place on a piece of cardboard or a tongue depressor and fix in 10% buffered formalin or freeze if facilities are available.
  • Skin is closed using sutures or staples.

techniques for neuromuscular disorders: equine motor neuron disease

  • As EMND primarily affects Type I or postural muscles, it is important to choose a muscle that contains predominantly Type I muscle fibers.
  • The tail head muscle, or sacrocaudalis dorsalis medialis is one such muscle and is easily accessible in the standing horse.
  • A surgical biopsy of this muscle can be taken using a technique similar to the semiembranosus/semitendinosus, although a smaller piece of muscle is usually obtained owing to the small size of this muscle.

techniques for localized muscle disorders

  • Surgical or needle biopsy from the affected muscle using the above techniques.

Sampling, handling and processing

  • Formalin:
    • 10% buffered formalin is the fixative used for most routine muscle diagnostic histopathology.
    • Ensure samples are not too large for the formalin, otherwise fixation of the central portions of muscle will not occur.
    • A maximum diameter of 1 cm should be placed into formalin.
  • Frozen:
    • Frozen samples are required for fiber typing and can reduce the fixation shrinkage artifacts sometimes seen with formalin fixed sections.
    • However, for routine clinical work, it is not necessary to use frozen sections and freezing can be difficult to accomplish without freezing artifacts.
    • To freeze samples, techniques include rolling the sample in talc prior to liquid nitrogen, cooling slowly on the surface of liquid nitrogen in an aluminium "boat", and freezing in liquid nitrogen cooled isopentane.
  • Laboratories:
    • Not all laboratories routinely process muscle and are comfortable interpreting the findings.
    • The Royal Veterinary College and the University of Edinburgh, in the UK, are 2 hospitals that routinely investigate equine muscle disorders.
    • It is advisable to call your laboratory to check if they are happy before sending or even taking your sample.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Stanley R L, Maile C & Piercy R J (2009) Storage-associated artefact in equine muscle biopsy sample. Equine Vet J 41 (1), 82-86.
  • Ledwith A & McGowan C M (2004) Muscle biopsy: a routine diagnostic procedure. Equine Vet Educ 16 (2), 62-67.
  • Valentine B A, Divers T J et al (1998) Muscle biopsy diagnosis of motor neuron disease and equine polysaccharide storage myopathy. Equine Vet Educ 10, 42-50.