Inclusion Body Myositis

Inclusion Body Myositis (IBM) (also referred to as sporadic inclusion body myositis, sIBM) is classified as a chronic, degenerative neuromuscular disease in which inflammatory cells invade muscle tissue causing progressive muscle weakness and wasting. IBM differs from other types of Myositis in that there is currently no known effective treatment for the disease.

IBM is known to cause slow, progressive asymmetrical weakness and atrophy of the muscles of the wrists and fingers, muscles in the front of the thigh, and muscles that lift the front of the foot. Patients who have the disease can gradually lose the ability to walk, experience falls and injuries, lose hand function, and have swallowing difficulties. Some patients also experience muscle pain.

The first muscles affected in Inclusion Body Myositis are usually those of the wrists and fingers, and the muscles at the front of the thigh. The muscles that lift the front of the foot also may be affected (see image to the right).

Muscle weakness is often asymmetrical, more prominent on one side than the other.

IBM is a rare disease affecting men more than women. Approximately 5 to 10 people per million in the U.S. are diagnosed with a form of Myositis each year.

Inflammatory and Non-Inflammatory Types

There are two types of Inclusion Body Myositis, both have similar symptoms, but the diseases differ in other aspects. Our focus is the inflammatory type of IBM, called sIBM.

Sporadic Inclusion Body Myositis (sIBM)

Sporadic Inclusion Body Myositis is the more prevalent form of IBM and is classified as an Idiopathic Inflammatory Myopathy, an inflammatory muscle disease with no known cause. It is also considered an Acquired Myopathy, one which is not caused by genetic inheritance.

It is the most common inflammatory muscle disease in adults older than 50 and is found in men more often than in women. Symptom onset occurs gradually, typically over a period of months or years, most often after the age of 50. It is not uncommon for people with IBM to become wheelchair bound within 10 to 15 years of disease onset.

The cause of inflammatory myopathies is unclear. For some reason, in the case of sIBM, the body’s immune system turns against itself, referred to as an autoimmune response, and damages muscle tissue. The cause of the progressive muscle degeneration that occurs in IBM is unclear as well.

IBM and ALS are similar in that  muscle-wasting occurs. Some patients with sIBM are actually diagnosed with ALS first.

Inherited Inclusion Body Myositis (hIBM)

Inherited Inclusion Body Myositis is a disease which is genetically inherited, often appearing in other family members, and frequently starts with muscle weakness in early adulthood, occasionally as early as the teen years. This form of the disease is not categorized as an Acquired Myopathy or an Idiopathic Inflammatory Myopathy.

The early symptoms include index finger weakness, difficulty walking, tripping and loss of balance. The disease typically progresses to the hands, shoulders, and neck. In this form of the disease, organs are rarely affected, nor are the muscles in the face and eyes, those used for breathing, digestion, and the heart.

Inflammatory cells invading muscle tissues is one characteristic of IBM, but the disease is distinct from other inflammatory myopathies in that muscle degeneration also occurs.

Inclusion Body Myositis is named for the clumps of discarded cellular material — the “bodies” — that collect in the muscle tissues. These are apparent on the pathology reports for a muscle biopsy.

Each case of IBM may be quite different from others.  There have been cases where people originally diagnosed with Polymyositis (PM) but were not responding to standard treatments later found they actually had IBM or a non-inflammatory Myopathy such as a form of Muscular Dystrophy.

Tool: Inclusion Body Myositis – Functional Rating Scale (IBM-FRS)

The Functional Rating Scale (IBM-FRS) for Inclusion Body Myositis can be used to help hospital staff better understand your needs. Download the file below and ask that it be made a part of your medical records.

Have you been diagnosed with sIBM?

Or, are you a direct caregiver to someone who has been?

We have a support group just for those living with sIBM, sporadic inclusion body myositis, and their direct caregivers.

As part of our commitment to help myositis patients, we have several online support groups. What makes the IBM support group helpful is that often the discussion surrounding IBM, vs. that of PM, DM, NAM, and other forms, is less about treatment options, since none currently exist, and more about learning to cope and live with this rare muscle disease.

And, since we know how difficult it can be for anyone with a muscle disease, we also allow a direct caregiver in the group as well. Support, both emotional and physical, along with education is paramount to living well with IBM.

If you have been diagnosed with IBM we hope you will request to join our group on Facebook at www.Facebook.com/groups/inclusionbodymyositis

IBM and other diseases

IBM is not typically associated with an increased prevalence of other diseases such as cancer, interstitial lung disease, or heart disease. Autoimmune disorders such as Sjögren’s syndrome, thrombocytopenia, and sarcoidosis have been reported in up to 15% of patients with sIBM. Life expectancy is not thought to be affected.

Muscle Wasting

The first muscles affected in inclusion body myositis are usually those of the wrists and fingers, and the muscles at the front of the thigh. The muscles that lift the front of the foot also may be affected. This image shows muscle wasting in the forearm into the hands and fingers. 

Muscle biopsy comparison of normal muscle tissue versus muscle tissues affected with Inclusion Body Myositis.  Inclusion Body Myositis is named for the clumps of discarded cellular material — the “bodies” — that collect in the muscle tissues.

Image courtesy of

The Muscular Dystrophy Association

Simply Put

“Simply Put” is a service of Myositis Support and Understanding, to provide overviews of Myositis-related medical and scientific information in understandable language.

MSU volunteers, who have no medical background, read and analyze often-complicated medical information and present it in more simplified terms so that readers have a starting point for further investigation and consultation with healthcare providers. The information provided is not meant to be medical advice of any type.