The triggers of inclusion body myositis are thought to be environmental triggers like viral infections as well as genetic predispositions, that trigger an autoimmune response and muscle degeneration.
Although inclusion body myositis is an idiopathic condition, which means that it's exact cause is unknown.
However the root causes and biological processes of inclusion body myositis are thought to be a result of a combination of several complex factors, which include genetic predisposition, aging, muscle degeneration and protein buildup and autoimmune response.
Sporadic IBM (sIBM) is typically not an inherited disease.
However, genetics are thought to play a role in a person's susceptibility to the condition.
Approximately 67% of IBM patients share a specific combination of human leukocyte antigen (HLA) genes (part of the 8.1 ancestral haplotype), which may make them more prone to developing the disease.
IBM is the most common muscle disease in adults over the age of 50, and onset under 50 is relatively rare.
The degenerative changes in muscle tissue are strongly linked to the natural aging process, oxidative stress, and the body's declining ability to clear out abnormal proteins over time.
Inclusion body myositis also gets its name from "inclusion bodies"—which are microscopic clumps of abnormal proteins and discarded cellular material that build up inside the muscle cells.
These accumulations cause small, empty spaces called "vacuoles" to form in the muscle fibers.
This degenerative process—the accumulation of misfolded proteins—interferes with normal cellular function and is characteristic of neurodegenerative conditions.
IBM or inclusion body myositis is also considered an inflammatory myopathy with a distinct autoimmune component.
The body’s immune system mistakenly attacks its own healthy muscle tissues, causing inflammation. However, unlike other inflammatory diseases, IBM often responds poorly to traditional immunosuppressive therapies, leading researchers to believe the immune reaction may actually be secondary to underlying muscle degeneration.
The life expectancy of someone with inclusion body myositis is often close to normal, although there can be a modest reduction in lifespan.
Most often though, people with inclusion body myositis pass away or die from aging related conditions or secondary complications, instead of the inclusion body myositis itself.
In most cases, the age at death for people with inclusion body myositis is around 79.3 years, when compared to the 83.6 years for people without inclusion body myositis.
Inclusion Body Myositis progresses very slowly and steadily over months and years and muscle deterioration with Inclusion Body Myositis is gradual and often around 3.5% per year.
In the early stages, Inclusion Body Myositis commonly targets your quadriceps (thighs) and your forearm/finger flexors, and you might notice frequent tripping, difficulty rising from a low chair or even have trouble gripping and pinching objects.
In the mid to late stages of Inclusion Body Myositis, over 10 to 15 years, the weakness with Inclusion Body Myositis, spreads and many people require mobility aids, like a cane, walker or wheelchair and up to 1/2 of all people with Inclusion Body Myositis, will also develop, difficulty swallowing, which is also known as dysphagia, over the course of the Inclusion Body Myositis.
Although IBM or Inclusion Body Myositis does not target the heart or affect breathing muscles early on, so life expectancy with Inclusion Body Myositis is often normal.
The first signs of IBM also known as Inclusion Body Myositis are frequent tripping and falls, foot drop, hand and finger weakness and difficulty standing or climbing.
Weakness in your quadriceps (thigh muscles) as a result of Inclusion Body Myositis can cause your knees to suddenly buckle or give way.
And foot drop with Inclusion Body Myositis is when you have difficulty in lifting the front part of your foot that causes your toes to drag, which leads to stumbling.
Hand and finger weakness as a result of Inclusion Body Myositis, involves loss of dexterity and grip strength, which results in trouble with fine motor tasks, such as turning a key, opening a jar or buttoning of a shirt.
And difficulty standing or climbing as a result of Inclusion Body Myositis can involve having trouble getting up from a low chair or stepping up onto curbs.
Early symptoms and signs of IBM or Inclusion Body Myositis, mainly involve slowly progressive muscle weakness in your fingers, wrists and thighs.
And people with Inclusion Body Myositis often experience frequent and unexplained trips and falls, which is often called "foot drop", weakened hand grips as well as difficulty rising from a seated position or climbing up stairs.
These early signs of Inclusion Body Myositis can easily be mistaken for the affects of normal aging, which also often results in a huge delay in diagnosis.
The early symptoms of Inclusion Body Myositis often manifest gradually over months or even years and they can also differ from person to person.
Other less common early symptoms of Inclusion Body Myositis or IBM include Dysphagia, which are swallowing difficulties and shoulder and arm weakness, where you have weakness in your arms and shoulder when attempting to reach overhead or comb your hair.
Symptoms are often brushed off initially when you have Inclusion Body Myositis because Inclusion Body Myositis primarily affects adults over age 50 and progresses so slowly.
Myositis is typically diagnosed through elevated levels of muscle enzymes (especially creatine kinase, aldolase, LDH, and AST/ALT) that leak into the bloodstream when muscle fibers break down. Autoimmune forms of myositis are further identified by positive antinuclear antibodies (ANA) and specific myositis-related autoantibodies.
The main laboratory markers for myositis can be broken down into three key categories:
1. Muscle Enzymes
When muscle tissue is damaged or inflamed, intracellular enzymes leak out and cause elevated blood levels.
Creatine Kinase (CK): The most specific and widely used blood test for muscle damage.
Levels can often reach 10 to 50 times the normal range, especially in acute myopathies.
Aldolase: Often elevated and sometimes used as a marker when CK levels are surprisingly normal.
Lactate Dehydrogenase (LDH): An enzyme found in muscle tissue (as well as the heart and liver) that frequently spikes during muscle breakdown.
AST and ALT (Aspartate Aminotransferase and Alanine Aminotransferase): While primarily thought of as liver enzymes, these are also highly concentrated in muscles. In myositis, they are often elevated in the absence of any liver issues.
2. Autoantibodies (Immune Markers)
Many types of myositis are autoimmune in nature. Doctors typically screen for these using blood tests to determine the specific subtype of the disease.
Antinuclear Antibodies (ANA): A broad screening test for autoimmune diseases. A positive ANA indicates an underlying immune issue but is not specific to myositis.
Myositis-Specific Antibodies (MSA): These pinpoint the exact type of myositis and help predict potential complications (such as lung or heart involvement).
Common examples include:
Anti-Jo-1: The most common myositis-specific antibody, often associated with lung disease (antisynthetase syndrome).
Anti-Mi-2: Frequently seen in dermatomyositis (typically with characteristic skin rashes).
Anti-SRP: Often tied to acute, severe muscle weakness and cardiac issues.
Anti-HMGCR: Seen in immune-mediated necrotizing myopathy (often linked to statin use).
3. General Markers of Inflammation
Myositis causes widespread or systemic inflammation, which can be detected by general blood tests.
C-Reactive Protein (CRP): A protein produced by the liver that spikes in response to inflammation.
Erythrocyte Sedimentation Rate (ESR): A blood test that measures how quickly red blood cells settle to the bottom of a test tube; an accelerated rate usually points to inflammatory activity in the body.