Inclusion body myositis (IBM) is the most common acquired muscle disease in patients over the age of 50. More men have inclusion body myositis than women, and the disease is rarely seen in people younger than 50 years of age.

Inclusion body myositis is unlike all other forms of myositis in terms of symptoms, treatment, and who it affects.  Symptoms of inclusion body myositis progress more slowly than the other types of myositis with weakness increasing gradually, sometimes over years. For this reason it is not uncommon for patients to realize that they had been experiencing symptoms for many years before they were diagnosed.

Inclusion body myositis symptoms

The following are common symptoms of IBM:

  • Frequent falls
  • Difficulty walking
  • Trouble climbing stairs or standing from a seated position
  • A foot that seems to drop when walking, causing tripping
  • Weakened hand grip and difficulty flexing the fingers
  • Difficulty writing, manipulating keys, and other activities requiring finger control
  • Weakness and noticeable shrinking of the quadriceps (main muscle of the thighs)
  • Weakness in the forearm muscles
  • Pain or discomfort as muscles weaken
  • Difficulty swallowing

Some of the first signs of inclusion body myositis are falling, difficulty getting up from a chair, and weakened grip. Muscles most often affected are those at the front of the thighs, those that elevate the feet, and those in the hips, fingers, wrists, upper arms, shoulders, neck, back, and, less often, in the face. Many IBM patients notice shrinking (atrophy) in the arms and thighs as the muscles become weaker. Trouble swallowing, or dysphagia, is a common problem for patients with IBM as well.

Inflammatory disease debate

There is currently some debate among myositis experts about whether or not inclusion body myositis is actually an inflammatory disease. Inflammatory cells are present in muscle tissue from patients with inclusion body myositis, especially earlier in the disease process, but their role in causing muscle weakness is unclear.

Autoantibodies have also been found in patients with IBM, suggesting an inflammatory process. However, the weakness appears to be the result of a degenerative process within the muscles, and the disease does not respond to treatment with anti-inflammatory medications.

Most experts agree, however, that an eventual treatment and cure will likely require attention to both inflammation and muscle degeneration.

IBM and hereditary inclusion body myopathies

Inclusion body myositis should not be mistaken for hereditary forms of inclusion body myopathy (also referred to as VCP or GNE myopathy). Although muscle biopsy findings in the hereditary myopathies share some of the same features seen in IBM—rimmed vacuoles and inclusions in muscle cells—these two conditions are otherwise quite different.

The hereditary form of the disease is caused by a gene defect, not inflammation. The average age of onset in the hereditary forms is between the teenage years and mid-twenties, not in older age. Muscle weakness is usually distal (in the extremities) and may include eye muscles and other areas of weakness. CK levels range from normal to slightly elevated, and EMG results are normal.

As you go through the diagnosis process, be sure to discuss these distinctions with your doctor.