Inclusion Body Myositis Health Article

Definition

Inclusion body myositis (IBM) is an inflammatory muscle disease characterized by progressive muscle weakness and wasting. The common feature of IBM is the abnormal finding of inclusion bodies, or granular material, in muscle fibers. The onset generally occurs gradually over months or years, and persons often experience falling and tripping as the first symptoms. Inclusion body myositis affects both proximal (closest to the center of the body) and distal (farthest from the center of the body) muscles.

Description

Sporadic inclusion body myositis is the most common muscle disease in people aged 50 years and older with an unknown cause. The disease was named in 1971, when scientists noted a case of myositis (muscle inflammation) that showed granular material in muscle fibers called inclusion bodies. The inclusion bodies are now recognized to contain abnormal deposits of amyloid proteins, similar to those found in the brain of patients with Alzheimer's disease. The deposits may represent a protein product left within the muscle fibers as they degenerate.

The onset of IBM is insidious, with symptoms often having been present for more than five years before diagnosis. The course of the disease is progressive over months or years, leading to severe disability. IBM may appear identical to another inflammatory myositis called polymyositis, although differences are clear in more than half of cases.

Weakness and impairment of muscle function are the hallmarks of IBM, and weakness distribution is variable, with both proximal (closest to the center of the body) and distal (farthest from the center of the body) muscles affected. Diminished deep-tendon reflexes and wasting (atrophy) of the involved musculature occur. Thus, loss of finger dexterity and grip strength may be present, while falling and tripping appear as the first signs. Patients often suffer from fatigue and reduced tolerance to exertion, and consequently become out of breath easily.