Inclusion body myositis

Inclusion body myositis (IBM) is a type of inflammatory myopathy. It is often considered is the most common acquired myopathy in patients older than 50.

Epidemiology

ItInclusion body myositis tends to present in older individuals ⁴ (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) ⁶.

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

ItInclusion body myositis is characterizedcharacterised 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

ItInclusion body myositis can affect both proximal (close to the trunk of the body) and distal (further away from the trunk) muscles. It is usually bileteralbilateral although Musclemuscle weakness may affect only one side of the body.    

Usual muscles involved include:

• quadriceps ⁶
• iliopsoas
• tibialis anterior
• deltoids
• biceps brachii ⁶
• triceps muscles ⁶
• finger flexors
• ankle dorsiflexors

Radiographic features

MRI

May show evidence of muscle oedema although this is not a specific feature. Abscess formation is generally not seen ¹.

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Treatment and prognosis

At the time of writing there is no definitive cure nor a standard course of treatment for IBMInclusion body myositis. The disease is generally unresponsive to corticosteroids and immunosuppressive drugs ⁴. There may be some evidencesuggestive a slight ,short, short lasting benefit from intravenous immunoglobulin therapy. Management is essentially supportive (physical therapy to improve mobility etc, etc).

Differential diagnosis

For MRI appearances consider:

• differential diagnosis of skeletal muscle oedema on MRI