Sporadic inclusion body myositis (sIBM) is the most common acquired myopathy in patients over the age of 50. It is unlike all other forms of myositis in terms of symptoms, treatment, and who it affects. More men have inclusion body myositis than women, and the disease is rarely seen in people younger than 50 years of age. 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.

There is currently some debate among myositis experts about whether or not inclusion body myositis is actually an inflammatory disease. On one hand, 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. In addition, autoantibodies have been found in patients with sIBM, suggesting an inflammatory process. On the other hand, 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.

Sporadic inclusion body myositis should not be mistaken for hereditary inclusion body myopathy (hIBM). Although muscle biopsy findings in the hereditary myopathies share some of the same features seen in sporadic 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 hIBM is between the teenage years and mid-twenties, not in older age. Muscle weakness in hIBM is usually distal (in the extremeties) and may include eye muscles and other areas of weakness. CK levels range from normal to slightly elevated, and EMG results are normal.

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 (dysphagia) is a common problem for patients with sIBM.

Signs and symptoms

  • 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 daily activities
  • 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