Inclusion-Body Myositis (IBM)

Diagnosis

Diagnosing inclusion body myositis (IBM) may require a combination of testing modalities. People with the disease may exhibit:

Test	Characteristic findings
Clinical symptoms	Signs indicative of IBM such as frequent falls, loss of hand/finger dexterity, etc.
Clinical exam	Asymmetric, distal muscle weakness and weakness in the hip flexors, knee extensors
Blood tests	Moderately elevated creatine kinase (CK) and other muscle enzymes Specific antibodies indicative of myositis or other autoimmune diseases
Myositis autoantibody testing	Myositis-specific autoantibodies: Anti-NT5C1A
Assessment of electrical activity in muscles/nerves	Distinctive pattern of electrical activity in affected muscles, as assessed by electromyogram Distinctive pattern of electrical activity in affected nerves, as assessed by a nerve conduction velocity test
Magnetic resonance imaging (MRI)	Signs of muscle thinning and tissue swelling (edema)
Muscle biopsy	Empty, bubble-like spaces (rimmed vacuoles) Clumps of cellular material (inclusion bodies) Inflammatory cells (e.g., cytotoxic T cells and macrophages) between the fibers Other characteristic findings

Muscle biopsy is still the gold standard in diagnostic testing for IBM. A biopsy sample from a person with IBM is unique because of its inclusion bodies, for which the disease is named. These “bodies” (which do not appear in normal cells) contain clumps of discarded cellular material. Inflammatory cells can be seen invading muscle tissue, although some researchers believe this invasion is secondary to the primary events in the muscle tissue, presumably those that cause the inclusion bodies to appear.

References

1. Inflammatory Muscle Diseases. N. Engl. J. Med. (2015). doi:10.1056/nejmc1506827
2. Lotz, B. P., Engel, A. G., Nishino, H., Stevens, J. C. & Litchy, W. J. Inclusion body myositis: Observations IN 40 patients. Brain (1989). doi:10.1093/brain/112.3.727
3. Greenberg SA. Inclusion body myositis: clinical features and pathogenesis. Nat Rev Rheumatol. 2019;15(5):257-272. doi:10.1038/s41584-019-0186-x
4. Naddaf E. Inclusion body myositis: Update on the diagnostic and therapeutic landscape. Front Neurol. 2022;13:2236. doi:10.3389/FNEUR.2022.1020113/BIBTEX

Last update: Feb 2023
Reviewed by Julie Paik, MD, MHS; Johns Hopkins University