Inclusion body myositis

A progressive muscle disorder

Inclusion body myositis (IBM) is a progressive muscle disorder characterized by muscle inflammation, weakness, and atrophy. It is one of the most common types of inflammatory myopathy in adults over the age of 50. IBM is distinguished by the presence of inclusion bodies in the muscle fibers, which are abnormal clumps of proteins.

Pathophysiology

Inclusion body myositis is considered both an autoimmune disease and a degenerative muscle disorder. The exact cause of IBM is not fully understood, but it involves an abnormal immune response that attacks the muscle tissue. This leads to chronic inflammation and the formation of inclusion bodies within the muscle fibers. These inclusion bodies contain proteins such as beta-amyloid, tau protein, and ubiquitin, which are also associated with neurodegenerative diseases.

Clinical Features

IBM typically presents with progressive muscle weakness and atrophy. The disease often affects the quadriceps muscles, leading to difficulty with activities such as climbing stairs and rising from a seated position. The forearm muscles and finger flexors are also commonly involved, resulting in difficulties with gripping and fine motor tasks. Unlike other inflammatory myopathies, IBM often affects the muscles asymmetrically.

Diagnosis

The diagnosis of inclusion body myositis is based on a combination of clinical features, laboratory tests, and muscle biopsy findings. Creatine kinase levels may be mildly elevated. Electromyography (EMG) can show characteristic patterns of muscle involvement. A muscle biopsy is crucial for diagnosis, revealing the presence of inflammatory infiltrates and inclusion bodies within the muscle fibers.

Treatment

There is currently no cure for inclusion body myositis, and treatment options are limited. Corticosteroids and other immunosuppressive therapies are generally ineffective. Management focuses on supportive care, including physical therapy to maintain muscle strength and function. Assistive devices may be necessary as the disease progresses.

Prognosis

The progression of IBM is generally slow, but it leads to significant disability over time. Most individuals with IBM will eventually require assistance with daily activities and mobility. The disease does not typically affect life expectancy, but it can significantly impact quality of life.

Related pages

• Inflammatory myopathy
• Autoimmune disease
• Muscle biopsy
• Neurodegenerative disease