Macrophagic myofasciitis is named for the findings seen in tissue from muscle biopsies. Microscopic examination has shown an abnormal infiltrate of specialized immune cells called macrophages surrounding muscle tissue. Macrophages are a type of immune cell that is important for swallowing and destroying microorganisms. They also assist other immune cells in the body's response to invading organisms. The muscle cells involved in patients with this disease appear to be minimally damaged by the macrophages.
The disorder is associated with an altered immune system in some, but not all, patients. A significant number of patients with macrophagic myofasciitis 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 despite fairly extensive investigations into known infectious and immune disorders which might cause muscle disease. A unique material that accumulates within the affected macrophages has been seen on electron microscopy. This material has yet to be characterized.
Most of the patients with macrophagic myofasciitis have responded to treatment with antibiotics and/or steroids within a few days or weeks. One patient with macrophagic myofasciitis and evidence of tuberculosis exposure recovered following treatment of the tuberculosis with four drugs.
With macrophagic myofasciitis, a mysterious new disease of muscle has been identified.