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Disclaimer: This article is for informational purposes only and is not intended for diagnostic use. LifeDNA does not provide diagnostic reports on any traits discussed. Genetics is just one piece of the puzzle; please consult a healthcare professional for comprehensive guidance on any health condition.
Inclusion Body Myositis (IBM) is a rare and progressive muscle disorder that primarily affects adults over the age of 50. It causes slow but steady muscle weakness, especially in the arms and legs. While IBM is often mistaken for other types of inflammatory muscle disease, it stands apart due to its unique cellular changes and resistance to most conventional treatments.
While the exact cause of Inclusion Body Myositis remains unknown, researchers have identified several contributing factors that appear to play a role in its development. These include autoimmune activity, abnormal protein buildup, and age-related cellular changes.
You might want to read: The Genetics of Age-related Muscle Mass Loss
The exact triggers of IBM are not fully understood, but researchers believe it develops due to a combination of immune system issues and underlying cellular defects. Key contributing factors include:
Autoimmune response
IBM is classified as an inflammatory myopathy, which means the body’s immune system mistakenly attacks its own muscle tissue. This autoimmune reaction leads to chronic inflammation and progressive damage to muscle fibers.
Protein misfolding and accumulation
A hallmark of IBM is the buildup of abnormal clumps (inclusion bodies) inside muscle cells. These clumps are made of misfolded proteins that the body fails to clear. The presence of these inclusions is what gives IBM its name and contributes to muscle degeneration.
Genetic susceptibility
While IBM is not typically inherited in a straightforward way, certain genetic aspects(like variations in the HLA-DRB1 gene) may increase the risk. These genetic variants may influence immune function or how cells process and remove damaged proteins.
Age-related changes
IBM mostly affects people over 50, suggesting that aging muscles may be more vulnerable to the underlying disease processes. As we age, the body becomes less efficient at managing inflammation and repairing damaged tissue.
IBM usually progresses slowly over several years, with symptoms that can vary from person to person. Common signs include:
Weakness in the thighs and forearms
IBM tends to affect specific muscle groups, particularly the quadriceps (front thigh muscles) and finger flexors (muscles used to grip). This leads to difficulty rising from chairs or holding objects.
Frequent falls and unsteady walking
Leg weakness often causes people with IBM to lose balance or trip easily. Falls become more common as the condition progresses.
Difficulty swallowing
Involvement of the throat muscles can make swallowing difficult, increasing the risk of choking or aspiration pneumonia.
Wasting or shrinkage of muscles
As muscle tissue deteriorates, visible muscle wasting (atrophy) may occur, especially in the forearms and thighs.
Slow but steady progression
IBM develops gradually over time and may take years before becoming significantly disabling. Unlike other forms of myositis, it typically does not respond to steroids or immunosuppressants.
 Research studies have looked at immune-related genes and found that certain variations in the HLA-DRB1 gene may increase the risk of IBM. These variations affect specific amino acid coding positions in the gene, possibly changing its function, which could help explain why some people are more likely to develop the disease. Another gene, CCR5, has also shown a possible link to IBM, suggesting there may be shared genetic features between IBM and other autoimmune diseases. In addition, rare genetic changes have been discovered in genes like VCP, SQSTM1, and FYCO1, which are involved in how the body breaks down damaged proteins. Studies also found large mitochondrial DNA deletions in certain muscle cells, suggesting that mitochondrial damage could be part of IBM as well. Similar findings have been reported by a more recent study on mitochondrial DNA variants in IBM. Altogether, these findings support the idea that IBM is caused by a combination of immune system problems, protein breakdown issues, and mitochondrial dysfunction. Scientists now believe that inflammation in the muscles may come first, leading to a buildup of damaged proteins and mitochondrial changes. Different research approaches have helped uncover these clues, and ongoing global studies are collecting more samples to improve future research. Larger studies that include diverse populations, along with advanced genetic testing methods like whole-exome and whole-genome sequencing, are expected to reveal even more about how genetics contributes to IBM.
While there is no known cure for Inclusion Body Myositis (IBM), supportive care can make a significant difference in a patient’s quality of life. Physical therapy plays an important role in helping maintain mobility and muscle strength through gentle, customized exercises that avoid overexertion. Occupational therapy is also valuable, offering practical tools and adaptations to support daily tasks as fine motor skills decline. As leg weakness progresses, mobility aids such as canes, walkers, or wheelchairs may become necessary to prevent falls and maintain independence.
For those experiencing swallowing difficulties, working with a nutritionist or speech therapist can help modify diets to ensure safe and adequate nutrition. Emotional support is equally crucial—living with a chronic, progressive condition can be isolating, so having access to support groups, therapy, and a strong social network can help ease the psychological burden. Regular visits to a neurologist are essential to monitor progression and manage emerging symptoms. In some cases, patients may also qualify for clinical trials exploring potential new treatments. A coordinated, multidisciplinary approach remains the best strategy for managing IBM over time.
Diagnosing IBM can be challenging because its symptoms often resemble other muscle diseases like polymyositis or ALS. However, there are several ways to confirm it:
Blood tests
These may show elevated muscle enzymes like creatine kinase (CK), but levels are usually only mildly increased in IBM.
Electromyography (EMG)
This test measures electrical activity in muscles and helps identify patterns consistent with IBM-related muscle damage.
Muscle biopsy
A definitive diagnosis usually requires a biopsy, where a small sample of muscle tissue is analyzed under a microscope. Inclusion bodies and other cellular changes are key markers of IBM.
Genetic and immune testing
While there is no standard genetic test for IBM, some individuals may benefit from genetic screening to identify genetic variants like those in HLA-DRB1. Research is ongoing into the genetic underpinnings of IBM, and new insights may shape future diagnostics.
If you’re experiencing unexpected muscle weakness or other concerning symptoms, speak with a healthcare provider. A neurologist or rheumatologist familiar with neuromuscular disorders is best equipped to assess and guide you through the appropriate tests.
