Do you know your antibody?

Many people don’t know which type of antibody they have. In a survey conducted by Know Rare through social media, we found only 2 out of 15 people diagnosed with myositis knew which antibody they had. Many people did not know the type of myositis they had, unless it was dermatomyositis marked by rashes. Very few of the survey responders had ever heard of the diagnosis of immune-mediated necrotizing myopathy (IMNM). When we followed up on the survey by asking a few myositis specialists in the US and in Europe how they describe the diagnosis to patients, the most common ways they explained it was simply as “myositis” or “autoimmune myositis.”

Antibodies associated with a myositis diagnosis

It is estimated that 45-85% of people with myositis have tested positive for myositis-specific antibodies (MSA) (depending on the accuracy of the test).

Diagnosis is not solely determined with an antibody test, but in necrotizing myopathies there are two different antibodies: the anti-HMGCR and the anti-SRP. The disease experience can be different, depending on which antibody someone has. The anti-HMGCR antibody tends to be more associated with people who have been taking statins. People with the anti-SRP antibody often experience more severe symptoms, with significant muscle weakness.

Those who test positive for the anti-synthetase antibody may be more likely to have some type of lung complications and Raynaud’s (a condition which causes some areas of the body — such as fingers and toes — to feel numb and cold in cold temperatures or when under stress).

How does a doctor determine if a myositis treatment is working?

Specialists’ approach to the treatment of myositis is individualized, taking into account the type of myositis, the degree of muscle weakness, age, how long since diagnosis, other conditions you might have, and other symptoms that affect the skin and/or lungs. Though the treatment most commonly prescribed for all myositis types (except IBM) are glucocorticoids (a type of corticosteroids that reduces inflammation) along with immune modulators, such as methotrexate, azathioprine, mycophenolate and rituximab, people with dermatomyositis may also be treated with anti-malarial drugs. For many, intravenous immunoglobulin infusions (IVIg) are used to get a quick response.

Doctors may monitor the level of a muscle enzyme, creatinine kinase (CK), to see how well the treatment is reducing high levels of the enzyme. In some cases of polymyositis, the CK levels may be 50 times the normal rate, and treatments aim to reduce it. The CK levels are a signal of the disease’s activity against the muscles, so if the numbers go down after treatment, it’s a sign the treatment may be working.

Sources:

1. Know Rare Myositis Survey. Fielded January 2021. 

2. Christopher-Stine, L. et al. Overview of and the approach to idiopathic inflammatory myopathies. Uptodate, 2022. www.uptodate.com. Accessed 8/20/2022.