inclusion body myositis
Inclusion body myositis (IBM) is a type of inflammatory myositis. It is often considered is the most common acquired myopathy in patients older than 50.
Epidemiology
Inclusion body myositis tends to present in older individuals (often after the age of 50), although the disease may occasionally present earlier. There may be a greater occurrence in males (M:F up to 3:1) .
Clinical presentation
The onset of symptoms is generally gradual (over months or years). Falling and tripping are often the first noticeable symptoms. In some cases individuals, the disorder begins with a painless weakness in the wrists and fingers that causes difficulty with pinching, buttoning, and gripping objects. There may be weakness of the wrist and finger muscles and atrophy (thinning or loss of muscle bulk) of the forearm muscles and quadriceps muscles in the legs. Difficulties with swallowing can occur in approximately half of cases.
Pathology
Inclusion body myositis is characterized by chronic, progressive muscle inflammation accompanied by muscle weakness.
Although it is classified as an inflammatory myopathy, inflammation is not considered a dominant component of the disease. The pathognomonic histologic feature of this condition is the presence of inclusion bodies in the nucleus and cytoplasm of affected muscle cells.
Location
Inclusion body myositis can affect both proximal (close to the trunk of the body) and distal (further away from the trunk) muscles. It is usually bilateral although muscle weakness may affect only one side of the body.
Usual muscles involved include:
- quadriceps
- iliopsoas
- tibialis anterior
- deltoids
- biceps brachii
- triceps muscles
- finger flexors
- ankle dorsiflexors
Associations
Recognized associations include :
- diabetes mellitus: ~20%
- other autoimmune conditions: ~15%
Radiographic features
MRI
May show evidence of muscle edema although this is not a specific feature. Abscess formation is generally not seen .
Treatment and prognosis
At the time of writing there is no definitive cure nor a standard course of treatment for Inclusion body myositis. The disease is generally unresponsive to corticosteroids and immunosuppressive drugs . There may be some evidence suggestive a slight, short lasting benefit from intravenous immunoglobulin therapy. Management is essentially supportive (physical therapy to improve mobility, etc).
Differential diagnosis
For MRI appearances consider:
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