Immune-mediated necrotizing myopathy (IMNM)

Immune-mediated necrotizing myopathy is a muscle disease in which the immune system is understood to drive the death of muscle fibers directly, with research describing deposits of immune complement proteins on damaged muscle cells and, in many cases, relatively little of the lymphocyte infiltration seen in other inflammatory myopathies. Two autoantibodies, anti-SRP and anti-HMGCR, are associated with distinct forms of the condition and help define its diagnosis, though some people test negative for both.

Contemporary research estimates it affects roughly 7 to 11 people per 100,000 annually in the United States, making it rare, and it typically produces more rapidly progressive weakness and higher muscle enzyme levels than related conditions. The disease process is only partly understood, and researchers are still working out why some cases respond better to treatment than others.

Common signs

Often rapidly developing and significant weakness in the muscles closest to the trunk, the hips, thighs, shoulders, and upper arms, making rising, climbing, and lifting difficult. Muscle aching and fatigue are common, and the weakness can be more pronounced than in some other muscle diseases.

This is a plain-language summary for orientation, not a diagnosis. Mechanisms are described as current understanding, not settled fact. Work with your own clinician for your care.