immune med muscle disorders review

Question 1

one of primary infectious agents that incite acute rhabdomyolysis

Answer 1

Streptococcus equi

causing infarctive purpura hemorrhagica (IPH), and immune-mediated myositis (IMM)

Question 2

Pathophysiology of infective purpura hemorrhagica

Answer 2

usually have had an infection within the past month, often with S. equi or a strangles vaccination.

often QH

In susceptible horses, the immune response results in high antibody titers to the SeM protein (>1:1600) and SeM-IgA immune complexes.

Question 3

Equine immune-mediated myositis predominantly happens in

Answer 3

Quarter Horses and related breeds (Paints, Appendix horses, and Appaloosas)

Question 4

How many horses have a history of infection when presenting with immune med myositis?

Answer 4

Of affected horses, 39% have a history of being recently exposed to a “triggering factor” such as S. equi infection, a respiratory virus

Question 5

which muscles are affected with immune mediated myositis

Answer 5

rarely generalized, and there is a

predilection for the gluteal and epaxial muscles

while other muscles such as the semimembranosus and semitendinosus muscles are relatively unaffected.

Question 6

which protein is specifically expressed with immune mediated myositis?

Answer 6

MHC histocomp complex on muscle cells

Question 7

treatment and prognosis of IMM

Answer 7

Anti-inflammatory doses of corticosteroid for approximately 1 month

combined with antibiotics if infection is present are often successful in halting muscle atrophy.

Muscle mass will regenerate over weeks to months, and horses can make a full recovery.

Almost 50% of horses will have recurrent episodes of muscle atrophy.

Question 8

A specific genetic defect and mode of inheritance have only been identified for which muscular diseases?

Answer 8

A specific genetic defect and mode of inheritance have only been identified in

hyperkalemic periodic paralysis [3],

glycogen branching enzyme deficiency [7], and

malignant hyperthermia

Question 9

malignant hyperthermia - which gene?

Answer 9

malignant hyperthermia in Quarter Horses with a mutation in the calcium release channel of the skeletal muscle sarcoplasmic reticulum, RyR1 gene

Question 10

hyperkalemic periodic paralysis -gene?

Answer 10

hyperkalemic periodic paralysis in Quarter Horses caused by a mutation in the a-subunit of the skeletal muscle sodium channel, SCN4A gene

Question 11

glycogen branching enzyme 1 deficiency- gene?

Answer 11

glycogen branching enzyme 1 deficiency in Quarter Horse and Paint foals due to a mutation in the glycogen branching enzyme 1, GBE1 gene

Question 12

Glycogen branching enzyme deficiency

Answer 12

fatal autosomal-recessive (only homozygot carriers affected) disease of Quarter Horses and Paint Horses caused by

Y34X missense mutation at codon 34 in exon 1 (C to A substitution at position 102 of coding sequence) of the glycogen branching enzyme 1 (GBE1) gene

Question 13

How many horses carry glycogen branching enzyme…

Answer 13

Approximately 8% of Quarter Horses and Paint Horses are carriers of GBED

Question 14

which part of dead foal provides diagnosis of GBED

Answer 14

Cardiac Purkinje fibers appear to consistently contain amorphous PAS-positive globular inclusions in affected foals

not always present in skeletal muscle

Question 15

PSSM most affected breeds?

Answer 15

Quarter Horses and related breeds (Paints and Appaloosas), draught horses (mainly Belgians and Percherons), and Warmbloods

Question 16

histopath diagnosis of PSSM?

Answer 16

presence of PAS-positive inclusions in muscle biopsies that are resistant to amylase digestion (

Question 18

Treatment of PSSM

Answer 18

Studies by Valberg and collaborators have shown that affected horses benefit from a combination of

daily regular exercise,

free exercise on pasture, and

dietary modification: includes high-fat (13%) and low starch (<10%) content of daily digestible energy

Question 19

when does malignant hyperthermia set off?

Answer 19

volatile anesthetics such as halothane,

depolarizing muscle relaxants such as succinylcholine,

and stress

Question 20

pathophysiology of malignant hyperthermia

Answer 20

mutations in the RyR1 gene cause

dysfunction of the calcium release channel of the sarcoplasmic reticulum in skeletal muscle,

resulting in excessive release of calcium into the myoplasm and a hypermetabolic state characterized by

intense heat,

hypercapnea,

lactic acidosis, and

in many cases, death

Question 22

diagnosis of malignant hyperthermia

Answer 22

difficult

muscle looks histolog normal

all ages and breeds

Question 23

Recurrent exertional rhabdomyolysis (RER) is the most prevalent muscle disease in

Answer 23

TB horses

It has been estimated that 5–10% of racing Thoroughbreds develop exertional rhabdomyolysis during a racing season with recurrences of up to 17%

Question 24

cause of RER

Answer 24

autosomal-dominant mode of inheritance with variable expression .

Recurrent Exertionl Rhabdo is believed to be caused by an abnormality in intracellular calcium regulation, and not by lactic acidosis

increased serum CK activity 4–6 h postexercise

Question 25

Pathophysiology of HYPP and clinical signs

Answer 25

4% of the Quarter Horse population may be affected

SCN4A gene mutation

• increased resting membrane potential,
• failure of a subpopulation of sodium channels to inactivate following depolarization, and
• excessive inward flux of sodium and outward flux of potassium

>>>resulting in persistent depolarization of muscle cells

Muscle hyperexcitability results in muscle tremors, fasciculations, and weakness that can progress to paralysis when muscle cells become persistently depolarized

Question 26

what triggers HYPP?

Answer 26

Diets high in potassium (>1.1%) such as alfalfa, soybean, molasses, electrolyte supplements, and kelp-based supplements commonly trigger episodes

Question 27

Lab diagnostics in HYPP

Answer 27

hyperkalemia (6–9 mmol/L; reference 3–5.6 mmol/L), mild hyponatremia, and hemoconcentration [74]. Serum CK is within reference values or may be mildly elevated a few hours post-episode.

e no specific histopathological findings in skeletal muscle