Researchers Find Viruses
Can Trigger IBM

Viruses, specifically a class known as retroviruses, may underlie at least some cases of inclusion-body myositis (IBM), say Marinos Dalakas at the National Institutes of Health and colleagues.

In a study published in the May issue of Annals of Neurology, the investigators describe four men infected with the human immunodeficiency virus (HIV) who also developed IBM. They note that they have so far seen a total of nine patients with HIV and IBM and another five with HTLV1 (human T-lymphocyte virus 1) and IBM, and that they don’t think the association is coincidental.

“It appears that certain genetically susceptible individuals who harbor the virus for many years can develop IBM,” they say, although they don’t believe that viruses are responsible for all IBM cases.

IBM is characterized by inflammation and degeneration of muscle tissue, and researchers have argued about whether the primary cause is a misguided immune system, resulting in inflammation and then muscle deterioration; or clumps of abnormal proteins causing muscle degeneration, with inflammation appearing secondarily.

A small percentage of IBM cases are directly genetic and run in families (familial IBM), but the majority of IBM cases are sporadic (nonfamilial).

Dalakas and colleagues propose that, in some sporadic IBM cases, the underlying cause is a virus, such as HIV, HTLV1 or another retrovirus, which then triggers an immune response that’s misdirected at muscle tissue.

They didn’t find any viruses inside muscle cells, but they did find them in nearby immune-system cells. They suggest that these immunologically active cells may send signals telling the immune system to attack the muscle fibers, and/or that when the immune system attacks a virus in the area, the muscle fibers are caught in the cross-fire.