Rare Daily Staff
Researchers at Washington University School of Medicine in St. Louis have identified a previously unknown autoimmune muscle disease involving sudden onset of debilitating muscle pain and weakness, an important finding because it can easily be mistaken for other muscle diseases that require different treatment.
The findings were published in the April 6 issue of the journal Neurology.
“We observed only four patients in more than 20 years, so it’s very rare,” said Alan Pestronk, a professor of neurology, and of pathology and immunology and senior author of the study. “It has never been described before, and it seems to be treatable, so it will be helpful for physicians to be aware of it. People don’t need to be afraid this is going to happen to them, but in the extremely rare event that it does, physicians should now have the tools to respond.”
Pestronk first observed the condition in 1996 while examining slides of the muscle cells of patient who experienced muscle pain and weakness. He noticed the patient had scavenger cells, which normally feed on dead material, crowding around injured muscle fibers. He continued to look for other cases over the next 22 years.
He discovered three more patients hospitalized for muscle pain and weakness whose biopsies showed muscle breakdown coupled with scavenger cells. By analyzing the biopsies, Pestronk and his colleagues discovered that the patients’ muscles were under assault by immune scavenger cells known as histiocytes. They dubbed the newfound syndrome large-histiocyte-related immune myopathy.
“There are several immune muscle diseases where the primary damage you see under the microscope is muscle fiber breakdown. Each of those diseases has a different prognosis and requires a different treatment,” Pestronk said. “Physicians need to recognize the immune nature of this condition in order to treat it appropriately.”
Three of the patients improved when treated with immunomodulating therapy such as steroids and have not relapsed since. The fourth was undergoing cancer treatment when the muscle symptoms developed, and he died due to cancer shortly afterward.
Pestronk noted that while muscle pain and weakness brought the patients into the clinic, all four were also anemic and had other shared symptoms. Accurately diagnosing people with the syndrome would help doctors manage and treat their other symptoms as well, he said.
Photo: Alan Pestronk, professor of neurology, and of pathology and immunology at Washington University School of Medicine