Large Animal Medicine Ruthie Reinken, Jessica Reese, Maritza Rodriguez
Large Animal Medicine
Ruthie Reinken, Jessica Reese, Maritza Rodriguez
9 year old Warmbloodgelding
Junior Equitation horse
With current owners since February
4-5 month progressive onset: Poor performance
Ataxia
Personality change
Two weeks prior to presentation, almost fell while handwalking
Previously treated with doxycycline and ponazuril with no improvement.
PE WNL
Neuro exam: Grade 1 ataxia in all 4 limbs
Weakness post-exercise
Quickly fatigued
Lameness exam: Grade 2/5 lame LF
Grade 2/5 lame RH
Weakness/ataxia
History stumbling, bucking
Lameness
Neuropathy Cervical spinal cord compression
EPM
Neuroborreliosis
Myopathy Polysaccharide Storage Myopathy (PSSM)
Nutritional (Vit E/Selenium deficiency)
Lameness/orthopedic
Diagnostic analgesia Bilateral abaxial
Nuclear scintigraphy
Neuropathy Cervical spinal cord compression
EPM
Neuroborreliosis
Myopathy Polysaccharide Storage Myopathy (PSSM)
Nutritional (Vit E/Selenium deficiency)
Lameness
Neuropathy Cervical spinal cord compression
EPM
Neuroborreliosis
Myopathy Polysaccharide Storage Myopathy (PSSM)
Nutritional (Vit E/Selenium deficiency)
Lameness
Neuropathy Cervical spinal cord compression
EPM
Neuroborelliosis
Myopathy Polysaccharide Storage Myopathy (PSSM)
Nutritional (Vit E/Selenium deficiency)
Lameness
Neuropathy Cervical spinal cord compression
EPM
Neuroborelliosis
Myopathy Polysaccharide Storage Myopathy (PSSM)
Nutritional (Vit E/Selenium deficiency)
Lameness
Neuropathy Cervical spinal cord compression
EPM
Neuroborelliosis
Myopathy Polysaccharide Storage Myopathy (PSSM)
Nutritional (Vit E/Selenium deficiency)
Lameness
Neuropathy Cervical spinal cord compression
EPM
Neuroborelliosis
Myopathy Polysaccharide Storage Myopathy (PSSM)
Nutritional (Vit E/Selenium deficiency)
Lameness
Muscle disorder in horses characterized by abnormal polysaccharide accumulation in skeletal muscle & clinical signs of rhabdomyolysis
1st recognized as a specific myopathy in 1992
Since then, the disease has been diagnosed in at least 35 different breeds in the USA and UK
Considered a common cause of neuromuscular disease in Quarter horse and Draft breeds
Affected horses were reported to have a 2-fold higher muscle glycogen concentration compared to normal horses Increase synthesis of glycogen, NOT an inability to
metabolize glycogen
2 linked biochemical abnormalities associated 1. Enhanced sensitivity to insulin in Quarter horses
2. Abnormal regulation of glycogen synthase
2 types of PSSM recognized
Mutation in glycogen synthase 1 gene (GYS1) resulting in excessive accumulation of
glycogen
Inherited in an autosomal dominant manner
The increased activity has an association with regulation of energy generation in muscle fibers during exercise under certain dietary conditions
Muscle samples from PSSM1 horses showed less than normal branched polysaccharide in the muscle fibers
Related to chronic enhanced activity of GYS1 gene Leads to less highly branched polysaccharide
Becomes resistant to amylase digestion when stained
Important for differentiation between PSSM type 1 and 2 via muscle biopsy
1st study differentiating Type 1 from Type 2 in 2009 (McCue et al)
Current knowledge based on retrospective studies of cases of diagnosed PSSM No genetic mutation associated
Origin is yet unknown
Valberg SJ. Muscling in on the Cause of Tying-Up. AAEP Proceedings/Vol.58/2012; 106-113
PAS stain Amylase-PAS stain
Type 1
Type 2
Highest prevalence appears to occur in draft horses derived from Continental European breeds
Valberg SJ. Muscling in on the Cause of Tying-Up. AAEP Proceedings/Vol.58/2012; 106-113
Highest prevalence appears to occur in draft horses derived from Continental European breeds
Valberg SJ. Muscling in on the Cause of Tying-Up. AAEP Proceedings/Vol.58/2012; 106-113
Estimates of PSSM1 in Quarter Horses range from 6-10% of the breed
Valberg SJ. Muscling in on the Cause of Tying-Up. AAEP Proceedings/Vol.58/2012; 106-113
Prevalence is low to nonexistent in light horse breeds Thoroughbreds, Standardbreds, Arabians
Valberg SJ. Muscling in on the Cause of Tying-Up. AAEP Proceedings/Vol.58/2012; 106-113
Warmbloods: about 80% of cases of PSSM diagnosed by muscle biopsy (Valberg 2012)
Quarter Horses: approximately 28% of cases of PSSM diagnosed by muscle biopsy (Valberg 2012)
Range significantly from one individual to another Pain Weakness recumbency Muscle atrophy Muscle spasms/fasciculations/contractions Gait abnormalities Poor performance Exercise intolerance Exertional rhabdomyolysis Other problems reported by owner – back soreness, difficulty trimming/shoeing rear
hooves, behavior problems under saddle or in harness, episodic spasmodic colic
Acute episode signs can last >2 hrs 10% become recumbent
Most affected muscles Gluteal, semimembranosus, semitendinosus, longissimus
Range significantly from one individual to another Pain Weakness recumbency Muscle atrophy Muscle spasms/fasciculations/contractions Gait abnormalities Poor performance Exercise intolerance Exertional rhabdomyolysis Other problems reported by owner – back soreness, difficulty trimming/shoeing rear
hooves, behavior problems under saddle or in harness, episodic spasmodic colic
Acute episode signs can last >2 hrs 10% become recumbent
Most affected muscles Gluteal, semimembranosus, semitendinosus, longissimus
Evidence of muscle-fiber necrosis: Elevated CK (>350 u/L) and AST (>420 u/L) 4-6 hours
after exercise
Other possible laboratory changes: Low blood selenium levels
Low vitamin E levels
Type I: Gold standard – genetic testing for GYS1 mutation Histopathology of muscle biopsy – PAS-positive amylase-
resistant inclusions in fast-twitch myofibers Risk of sampling error and false negatives
Type II: Histopathology of muscle biopsy – subsarcolemmal
aggregates of PAS-positive, amylase-sensitive (usually) glycogen Risk of false positives
Histopathologic findings don’t always correlate with severity of clinical signs or with increase in CK or AST post-exercise
Long-term therapy:
Diet change Very high in fat, high in fiber, low in starch and
sugar Goals: Decrease glucose load, increase availability of
NEFA for muscle metabolism, lower serum insulin levels
How is this achieved? At least 20% of total calories should be from fat
additive
Feeds should contain less than 33% starch/sugar
Hay with 12% or less non-structural carbohydrate to prevent insulin concentration increases
Regular daily exercise/turnout
Response to treatment takes up to 4 months for full fat adaptation
Good chance for return to acceptable performance-Variability in prognosis is based on severity of individual’s
clinical signs
PSSM horses will always have an increased tendency to have muscle soreness
CK
Pre exercise: 125 U/L
Post exercise: 134 U/L
Muscle biopsy
Results pending
Neuropathy
Cervical spinal cord compression EPM
Neuroborelliosis
Myopathy Polysaccharide Storage Myopathy (PSSM)
Nutritional (Vit E/Selenium deficiency)
Lameness
Thank you Dr. Sweeney
Dr. Tomlinson
Dr. Moore
Dr. Johnson
Dr. Davidson
Our rotation mates, Sam, Annie, and Alex
McCue ME, Armien AG, Lucio M, et al. Comparative skel-etal muscle histopathologic and ultrastructural features in two forms of polysaccharide storage myopathy in horses. Vet Pathol 2009;46:1281–1291.
McCue ME, Valberg SJ. Estimated prevalence of polysac-charide storage myopathy among overtly healthy Quarter Horses in the United States. Am J Vet Res2007;231:746–750.
McCue ME, Anderson SM, Valberg SJ, et al. Estimated prevalence of the type 1 polysaccharide storage myopathy mutation in selected North American and European breeds. Anim Genet 2010;41 (Suppl2):145–149.
McCue ME, Ribeiro WP, Valberg SJ. Prevalence of poly-saccharide storage myopathy in horses with neuromuscular disorders. Equine Vet J Suppl2006;36:340 –344.
Valberg SJ. Muscle disorders: Polysaccharide storage myopathy, in Proceedings. Am Assoc Equine Pract 2006;52:373-380.
Valberg SJ. Muscling in on the Cause of Tying-Up. AAEP Proceedings/Vol.58/2012; 106-113
Valentine BA. Equine polysaccharide storage myopathy: tutorial article. Equine vet Educ. 2003; 15 (5): 254-262.
Valentine BA, Van Saun RJ, and Thompson KN. Role of dietary carbohydrate and fat in horses with equine polysaccharide storage myopathy. JAVMA 2001; 219(11): 1537-1544.