Inclusion Body Myositis (IBM)

Characteristics

Inclusion Body Myositis (IBM) is a slowly progressive disorder of skeletal muscle tissue, typically manifesting after the age of 40. The male-to-female prevalence ratio is approximately 2:1. Muscle weakness is often asymmetrical and predominantly affects ventrally located muscles. Early symptoms commonly relate to weakness in the quadriceps, wrist and finger flexors, and pharyngeal muscles. This weakness can result in frequent falls, reduced grip and pinch strength, food stasis, and aspiration. Contractures and respiratory insufficiency may also occur. There is no evidence of cardiac involvement. IBM is associated with various autoimmune conditions, and in rare cases, a familial occurrence has been reported.

The rate of progression varies between individuals and within muscle groups of a single individual, averaging 3.5–5.5% loss of muscle strength per year. The disease ultimately leads to severe disability. About 13% of patients opt for palliative sedation or euthanasia in the late stages of the disease.

Serum creatine kinase levels are elevated by 0–12 times the normal range, and approximately 30% of patients test positive for antibodies against anti-cytosolic 5’-nucleotidase 1A.

The diagnosis is made through histopathological examination of a muscle biopsy, often guided by prior MRI imaging to localize the biopsy site. Several diagnostic criteria exist, primarily for research purposes, with the most widely used being the European Neuromuscular Centre (ENMC 2011) criteria.

Cause

The cause of IBM remains unknown. It exhibits features of both a degenerative and an inflammation-mediated disorder. Protein accumulation is observed in the sarcoplasm and nucleus of muscle cells. Additionally, a CD8-mediated inflammatory response is prominently involved.

Treatment

Currently, no pharmaceutical treatments are available for IBM. In cases of severe dysphagia, a cricopharyngeal myotomy can often provide temporary symptom relief. Ongoing international clinical trials are exploring potential treatment options.

Notes:

• Rate of Progression: The variability in progression underscores the importance of personalized care strategies.
• Diagnostic Tools: MRI-guided biopsy improves diagnostic accuracy.
• Clinical Research: Emerging therapies from trials may provide hope for future treatment options.