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Researchers at the University of Washington School of Medicine in St. Louis have discovered an autoimmune muscle disorder previously unknown, causing the sudden onset of debilitating muscle pain and weakness. The syndrome could easily be confused with other muscle diseases requiring different treatment, so the results should help doctors treat patients appropriately, the researchers said.
We have only seen four patients in more than 20 years, so it is very rare. Since this has never been described before and it seems to be treatable, it will be helpful for doctors to know it. People do not need to worry that this will happen to them, but in the extremely rare case, doctors should now have the tools to respond. "
Lead author Alan Pestronk, MD, Professor of Neurology, Pathology and Immunology
The results are available in the April 6 issue of the journal Neurology.
In 1996, Pestronk, who runs the University's Neuromuscular Diseases Clinic, was examining the muscle microscope slides with muscular pains and weaknesses while he was seeing something weird: Trapping cells that normally feed on dead material were clogged with injured muscle fibers.
"It was a pretty unusual situation for me to keep it in my memory and stay on the lookout for other cases like this," said Pestronk.
Over the next 22 years, he met three other hospitalized patients with muscle aches and weaknesses whose biopsies revealed muscle breakdown coupled with scavenging cells. By carefully badyzing the biopsies, Pestronk and his colleagues found that the patient's own muscles were attacked by tricky immune cells called histiocytes. They named immune myopathy related to large histiocytes.
The disease also reflects a new way in which the immune system can damage muscle cells. Understanding how immune cells damage muscle fibers could help prevent this damage.
"There are several immune muscle diseases for which the main damage under the microscope is the breakdown of muscle fibers – each of these diseases has a different prognosis and requires different treatment," said Pestronk. "Physicians must recognize the immune nature of this disease in order to treat it appropriately."
Three of the patients improved on immunomodulatory therapy, such as steroids, and have not re-offended since. The fourth was following cancer treatment when muscle symptoms developed and he died of cancer soon after.
In addition, while muscle pain and weakness brought patients to the clinic, all four were anemic and shared other symptoms. An accurate diagnosis of the syndrome would help doctors manage and treat their other symptoms, Pestronk said.
The condition could also be confused with rhabdomyolysis, a condition in which muscle fibers break down due to injury, excessive physical exercise or other reasons. This syndrome generates results similar to those of rhabdomyolysis during a blood chemistry. But people with rhabdomyolysis usually recover from themselves, while the new syndrome can be effectively treated with anti-inflammatory drugs.
Source:
University of Washington School of Medicine
Journal reference:
Pestronk, A. et al. (2019) Immune myopathy with large myofibers necrosis related to histiocytes. Neurology. doi.org/10.1212/WNL.0000000000007260.
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