Macrophagic myofasciitis: A muscle disease first identified in 1993, macrophagic myofasciitis is named for the findings seen in tissue from muscle biopsies, namely an abnormal infiltrate surrounding muscle tissue of specialized immune cells called "macrophages," a type of immune cell important to swallowing and destroying microorganisms. They also assist other immune cells in the body's response to invading organisms.The cause of macrophagic myofasciitis is not known. Suspected causes include environmental factors, which may be toxins or infections.
The disorder is associated with an altered immune system in some, but not all, patients. A significant number of patients had taken chloroquine or hydroxychloroquine for malaria; these drugs are known to inhibit the secretion from macrophages of a cell messenger molecule called interleukin. The cause of macrophagic myofasciitis has not been identified. A unique material that accumulates within the affected macrophages has been seen on electron microscopy but this material has yet to be characterized. Most patients have responded to treatment with antibiotics and/or steroids within a few days or weeks.