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EQUINE DISEASE: MYOGLOBINURIA
Rhabdomyolysis = Muscle destruction/damage
Myoglobinuria is an equine disease caused by the presence of myoglobin in the urine.
Myoglobin is a protein found in muscles, which transport oxygen to muscle cells. It is similar to haemoglobin in its function – they are both proteins that contain haem, but they are structurally different. When muscles are damaged myoglobin is released into the bloodstream to be excreted by the kidneys. Myoglobinuria is the equine disease caused by presence of myoglobin in the urine. Once myoglobin is released from muscles it is taken up by haptoglobins - a process that becomes rapidly saturated. The excess remaining myoglobin then enters the kidney tubules which lead to obstruction and subsequent renal failure.
CAUSES OF EQUINE DISEASE MYOGLOBINURIA
Any causes of muscle breakdown can contribute to the equine disease Myoglobinuria:
- Burns – burning/crawling sensation in the muscles, leads to muscle damage and thus myoglobinuria
- Status epilepticus – due to constant muscle contraction, this will lead to muscle damage and therefore myoglobinuria
- Myocarditis – inflammation of the heart muscle
- Acute tumour lysis - massive tumour breakdown which occurs after starting chemotherapy
- Major disasters e.g. earthquakes
- Meyer-Betz disease - muscle pain, weakness and myoglobinuria following strenuous exercise
- Genetic disorders e.g. Glycogenosis type 5 and Phosphoglycerate mutase 2 deficiency
- Snake venoms e.g. beaked sea snake/canebrake rattlesnake
- Drugs e.g. heroin, diazepam, ethylene glycol
SYMPTOMS OF EQUINE DISEASE MYOGLOBINURIA
Rust-coloured urine – is direct proof of myoglobinuria
Myoglobin in the urine
In cases where myoglobinuria is asymptomaticdetection is of more significance than symptoms.
Detection of equine disease myoglobinuria
- Myoglobin in the urine usually darkens the urine.
- The equine disease Myoglobinuria can cause a positive urine dipstick for blood, thus being confused with haematuria
- Urine microscopy specifically looks for red blood cells. A lack of RBC's with a positive dipstick for blood indicates myoglobinuria
- Immunoassays is a direct test for myoglobinuria
EQUINE DISEASE MYOGLOBINURIA-CAUSES
- Crush Syndrome – Also known as Bywaters' syndrome: A trauma or accident involving the crushing of soft tissues and associated symptoms. Severe cases can result in death.
- Myocarditis - Inflammation of the myocardium (muscle walls of the heart).
- Glycogenosis type 5 – Also known as McArdle disease: A rare inherited glycogen storage disorder involving a deficiency of muscle phosphorylase needed to convert glycogen to glucose in the muscles.
- Burns – burning or crawling sensation in the muscles. Indication damage to the muscle and this can lead to myoglobinuria.
- Muscle phosphoglycerate mutase deficiency - A rare inborn error of metabolism where an enzyme deficiency (muscle phosphoglycerate mutase) affects the muscles, especially during periods of strenuous activity.
- Myositis - One of the underlying causes for muscle weakness/myopathy, thus leading to myoglobinuria
- Meyer-Betz disease - a necrotising disease affecting exercising muscles, and therefore directly linked to the development of myoglobinuria.
TREATMENT OF EQUINE DISEASE MYOGLOBINURIA
This is the treatment for equine disease rhabdomyolysis – a specific type of Myoglobinuria.
- Prompt fluid rehydration aids in the initial control of myoglobinuria
- Alkaline diuresis - alkalinisation of the urine with bicarbonate can reduce the risk of acute renal failure
- Hyperkalaemia must be treated
- Diuretics (should not be used until hypovolaemia is corrected)
- If renal function fails to improve the horse is at risk of acute tubular necrosis (this is the death of tubular cells, which may result when tubular cells do not get enough oxygen) - in which case haemodialysis may be necessary