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Case Study 1: Atypical Myopathy

Rubi’s owner called us in the early hours of the morning after noticing that her young mare seemed unexpectedly lethargic after a short hack the previous afternoon. She had been diligently checking Rubi every couple of hours into the night and at around 2am it became apparent that she wasn’t improving and most definitely wasn’t well.

On examination Rubi appeared quiet but otherwise alert and responsive. Her muscles were slightly tightened as you would expect with a mild exertional myopathy (‘Tying Up’) and her heart rate was abnormally elevated given the fact that she was relaxed in her stable. We took a blood sample and monitored her closely for any deterioration in signs and her owner monitored her for abnormally dark coloured urine. The owner was not aware of any sycamore seeds being present in the paddocks at this stage.

Before the blood results had been received Rubi’s owner called to say that she had passed some dark chocolate-coloured urine and that sycamore seeds had been found in the field. The blood results came back later that morning with extremely elevated muscle enzymes indicating muscle damage and widespread severe inflammation with values consistent with Atypical Myopathy. Rubi was promptly given aggressive fluid therapy, multivitamins, muscle relaxants, antibiotics and anti-inflammatories. We did not want to risk transporting her for fear of worsening the muscle damage so her owner and owner’s friend took shifts through the night to maintain her IV fluid line, change her fluids and continue to give her medication overnight. Despite remaining quiet Rubi never lay down and continued to be able to eat and move around the stable as normal. We persevered with treatment despite an initial decline in her blood work but as the days passed Rubi turned a corner and her muscle enzymes started normalising.

Rubi pulled through thanks to the owner spotting that her horse was not right and alerting us so quickly. This enabled us to treat Rubi immediately and therefore prevent significant deterioration, giving her the chance to fight the disease. It is extremely rare for any case to service once the horse has become recumbent for any length of time. The fact that the owner had the perfect set up of a stable with a rail above for hanging fluids and the time to monitor her 24 hours a day also contributed hugely to the successful outcome.

Equine Atypical Myopathy is a disease which is fatal in around 70% of cases. It is a disease of the muscles caused by a toxin which breaks the muscles down into products which have to be filtered through the kidneys. As the kidneys attempt to rid the body of these products they become heavily (and sometimes irreparably) damaged. The toxin, called ‘Hypoglycin A’ is found in Sycamore Seeds.

Initial signs are non-specific with affected horses appearing quiet and lethargic but the disease will quickly progress with the horse showing muscle fasciculation (severe trembling), sweating, inappetance, colic like signs and dark coloured urine. At this stage, the horse will soon become recumbent and treatment is usually hopeless as the heart and lungs will start to fail.

Unfortunately the disease can progress so quickly that some horses are found dead in their fields with sycamore seeds still in their mouth. We are more likely to be able to successfully treat the disease if:

  • The horse has no other underlying systemic disease (such as Cushing’s disease) which may reduce the immune system.
  • The horse has only ingested small amounts of the toxin.
  • The horse is still standing and able to walk.

Treatment of the disease involves aggressive intravenous fluid therapy (this will require hospitalisation in almost all cases), anti-inflammatory medication, sedation, strong painkillers, muscle relaxants and antibiotics. Blood samples are taken as often as twice daily to enable monitoring of the muscle enzymes (CK, AST and LDH) in the blood. Due to the intensive nature of the treatment it can be very costly and therefore something we would recommend insuring your horse against.

The vast majority of cases are seen in the autumn when the seeds have recently fallen onto pasture. It is advisable to fence off space around sycamore trees in paddocks or to manually rake up fallen seeds if fencing off is difficult. It is possible for the disease to occur in the spring and summer too although cases are seen in far fewer numbers. These cases are believed to be the result of ingestion of Sycamore seedlings which have germinated and taken root over the winter. In 2014, we saw almost 10 times more cases than in any other year. It seems that certain weather conditions have a massive effect on how prevalent the disease is year on year.

The severity of the disease may relate to the amount of seeds ingested but some horses seem to be more susceptible than others. We have seen many more cases in younger horses and whilst it is possible for the disease to occur in older horses it is likely that they may have some level of resistance to the toxin. New research has shown that Hypoglycin A is not present in every seed or in seeds from every tree. Atypical Myopathy is not contagious so cannot be passed from one horse to another.

We would suggest any horses showing signs of weakness and increased periods of recumbency (lying down) are stabled and monitored closely. Tape a clear plastic pot onto the end of a broom handle and collect a sample of urine when the horse next urinates. If the urine looks red / brown or black then call the practice urgently. If the urine is yellow or clear then it is unlikely that your horse is affected. Horse urine has a wide range of normality. It can be watery and clear through to gloopy, thick and dark yellow. If you are at all unsure please bring a sample into the practice for a dipstick test.

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