Page 476 - The Veterinary Care of the Horse

Clinical signs

There is a whole spectrum of clinical signs ranging from exertional rhabdomyolysis
VetBooks.ir syndrome (ERS) (see page 303) to more subtle signs of poor performance. There are some

horses with PSSM1 that show no clinical signs.
The following may be seen:

• Firm, painful muscles

• Stiffness

• Abnormal sweating

• Reluctance to work
• Exercise intolerance

• Exertional rhabdomyolysis syndrome (ERS)

• Abnormal hind limb gait

• Stopping when ridden and adopting the urinating position
• Discoloured brown urine

• Tremors of the flank muscles

• Pawing the ground

• Rolling
• Intolerance of trimming and shoeing the hind feet

• Inability to stand up in severe cases

This can then lead to:
• Muscle wasting

• Progressive weakness

• Behavioural problems as a result of the pain

• Increased risk of myopathy following a general anaesthetic

The muscles of the back, rump and hamstrings are most severely affected, i.e. the
longissimus dorsi, gluteals, biceps femoris, semimembranosus and semitendinosus.

Diagnosis

A biopsy is taken from the gluteal or semimembranosus muscle and sent to a specialist
laboratory that regularly examines muscle samples. When stained and viewed under the