White Muscle Disease

Nutritional myodegeneration (NMD) associated with inadequate selenium and perhaps Vitamin E in diet. Seen in Pacific Northwest and Eastern states in equine neonates [1]. May also be precipitated by birth asphyxia and oxidative stress. There are two types of the disease based on the organs affected: the peracute or cardiac form and the skeletal or sub acute form.

I. Clinical Signs

Peracute or cardiac form

1. Fulminant onset.
2. Animals found dead or exhibit cardiac failure, or cardiogenic shock.
3. Intercostal muscles and diaphragm may also be affected.

Subacute or skeletal form

1. Signs from birth to 11 months of age.
2. Weakness - Unable to rise without assistance, falls on attempting to rise, often resembles colic.
3. Dysphagia - Seen as oral and nasal regurgitation of milk.
4. Stiff painful gait or neck.
5. Tense or painful muscles.
6. Temperature may be elevated due to thrashing and straining and secondary infections.
7. Elevated respiratory rate.
8. Dark urine

II. Clinical Pathology [2]

1. Elevated serum CK (subtypes for myocardium or skeletal muscle can be differentiated)
2. Elevated serum AST
3. Elevated LDH
4. Occult blood or myoglobin in urine.

1. Dip stick orthotoluidine reagent reacts with both blood and myoglobin.

5. Low serum glutathione peroxidase activity

1. Submit whole blood in EDTA tube.
2. Normal level is 20-50 U/mg of hemoglobin/min.

6. Low blood selenium <0.07 ppm suggests deficiency.
7. Vitamin E level should be >1-2 ppm
8. Hyperkalemia and hyponatremia can be severe.

III. Differential Diagnosis

1. Botulism

1. Lack tone to muscles.
2. Shaking of muscles.
3. Dilated pupils
4. Weak eye lids

2. Hemolytic Anemia
3. Polyarthritis
4. Tetanus
5. Asphyxia
6. Polysaccharide storage myopathy
7. Glycogen branching enzyme deficiency
8. Malignant Hyperthermia [3]

1. Recently described and gene identified by Dr. Monica Aleman - horses have similar signs of "white muscle disease". Test all suspect cases for MH (See Congenital Anomalies and Genetic Disorders).

IV. Treatment

1. Vitamin E - Selenium injection - 1 ml E-Se/45 kg IM. It may need to be repeated daily or q 2-6 weeks. Also use oral vitamin E 1000 unit/day during acute phase.
   Editor's Comment - Use natural form of alpha tocopherol and not synthetic - better absorption.
2. Supplementation of pregnant mares at risk.

1. 1 mg/day Selenium to ration.
2. 10 ml Vitamin E-Se® intramuscularly.

3. Metabolic support - I.V. fluids, correction of hyperkalemia (See Fluid and Electrolyte Balance, Enteral Nutrition) and hyponatremia, diuresis for myoglobinuria, limit movement.

V. Prognosis is poor to guarded, treatment must be started early to be beneficial