Myositis is one of the rarer forms of autoimmune diseases having an annual incidence of 2 to 10 cases in a million. So yes, very rare! There are multiple forms of inflammatory myositis. In my adult rheumatology practice, I mainly see polymyositis and dermatomyositis, but there are other types.
- Polymyositis
- Dermatomyositis (DM)
- PM/DM associated with cancer (12% of all myositis cases; 50% of myositis cases in people aged >65 years)
- Juvenile dermatomyositis
- Overlap syndrome (e.g., concurrent scleroderma and myositis, accounts for 11 to 40% of cases)
- Inclusion body myositis
- Giant cell myositis
Non-autoimmune forms of myositis are those caused by infections as well as drugs and toxins.
Who gets myositis?
That really depends on what form of myositis we are talking about. For example, the incidence of dermatomyositis is bimodal meaning that it has two peaks: 5-10 years of age and then 45-65 years of age. Polymyositis tends to occur later in life: 50-60 years of age. In general, like many other autoimmune diseases, women tend to be affected more than men: 2-3:1. Childhood cases are pretty much equal. Moreover, in the US African Americans are more commonly affected as compared to caucasians: 3-4:1.
What are the signs and symptoms of myositis?
Muscles
One would think that muscle pain would be the most prominent symptom seen in myositis. But actually it isn’t.
Muscle weakness involving the arms, shoulders, hips, and legs are the earliest signs of myositis.
Typically, symptoms progress over the course of 3 to 6 months. At times muscles used to speak, swallow, and breathe can be affected as well. People often experience low grade fevers, fatigue, and weight loss.
Sometimes, myositis can affect the heart causing myocarditis. This can then cause abnormal heart rhythms. This isn’t common though.
However, if there are symptoms involving the face or eyes, then we may be dealing with another form of myopathy. Not myositis.
Skin and nails
Many people with myositis develop Raynaud’s phenomenon. People who develop Raynaud’s experience a painful blanching of the fingers when exposed to the cold or in stressful situations. Your rheumatologist may use a special instrument to look at your blood vessels supplying your nail. I wrote about Raynaud’s in a previous article. Please follow the link to learn more.
People suffering from dermatomyositis may experience a host of different rashes. Please follow this link for pics.
- Heliotrope rash
- Gottron’s papules
- V-sign
- Shawl-sign
- Holster-sign
- Skin ulcers
- Livedo reticularis
People with myositis, particularly those with what we call anti-synthetase antibodies can develop something called Mechanic’s hands.
Finally, people with dermatomyositis particularly in juvenile cases, can develop calcinosis. These are calcium deposits that form under the skin and in muscles and tendons. We also see these in scleroderma, lupus, and mixed connective tissue disease.
Lungs
Myositis can cause a host of different pulmonary manifestations. Because the diaphragm is a muscle, people often experience shortness of breath. They are also prone to develop aspiration pneumonia. This happens when someone inhales regurgitated food, which then causes pneumonia.
People suffering with myositis, particularly those with antisynthetase antibodies also can develop interstitial lung disease and pulmonary fibrosis. This occurs when there is inflammation within the lung. If left untreated, it can cause stiffness and hardening of the lung.
Pulmonary hypertension can also happen. This occurs when the pressure in the pulmonary artery increases, which in turn increases strain on the heart and can result in heart failure.
Gastrointestinal
Myositis affects the GI tract as follows:
- Esophageal dysmotility
- Reflux
- Stool incontinence
- Intestinal perforation (particularly in juvenile cases)
Musculoskeletal
Inflammatory arthritis can sometimes be seen: joint pain, swelling, and morning stiffness lasting more than one hour. This mainly occurs with antisynthetase antibodies, but also in overlap cases. e.g., polymyositis + rheumatoid arthritis.
How do we make a diagnosis of myositis?
Like most rheumatic diseases, a single lab test does not make or break a diagnosis. A rheumatologist may obtain any of the following to help establish the diagnosis but also help determine which organs are involved:
- Identify clinical signs and symptoms: muscle fatigue, rash, etc.
- Blood tests that detect muscle damage: CK, aldolase, LDH, elevated AST and ALT. Sometimes muscle enzymes can leak into urine.
- Antibodies associated with myositis: Jo-1, Mi-2, anti-155/140 antibodies, Ro-52 etc.
- Electromyogram: “nerve conduction tests”
- Muscle biopsy
- Skin biopsy if there’s a rash
- MRI of an affected limb
- Pulmonary function tests
- Echocardiogram
- Electrocardiogram (EKG or ECG depending on which side of the Pond you reside)
- Right heart catheterization
- Swallow test
- CT of the chest, abdomen, and pelvis
If the presentation is classic and there is sufficient supporting data, at times a rheumatologist may skip the muscle biopsy. For example, if someone has muscle weakness, high muscle enzymes, a classic dermatomyositis rash, and positive antibodies.
Do steroids affect the results of a muscle biopsy?
No. Shinjo and colleagues studied the effects of prior steroid use in people undergoing a muscle biopsy. They found that if a person was experiencing active symptoms and their labs showed active disease, the muscle biopsy tended to to show active inflammation as well, despite prior use of steroids.
Can statins cause myositis?
Statins are a class of medications commonly prescribed to treat high cholesterol. About 1 in 10,000 people receiving low doses and 1% of people receiving high doses of statins can develop muscle pain and cramps. A very small percentage of these people can develop polymyositis. The muscle biopsy looks very different in these situation: necrosis without inflammation. These people also tend to have anti-200/100 antibodies also known as anti-HMG-CoA reductase antibodies.
Do people with myositis have a higher risk for cancer?
First, myositis is extremely heterogenous. There are certain forms of myositis that have a higher risk of cancer. About 12% of inflammatory myositis cases are associated with cancer, but about 50% of dermatomyositis cases occurring above the age of 65 year are.
There are also certain risk factors that increase the risk, such the presence of skin ulcerations and having anti-155/140 antibodies. However, people with a Mi-2 antibodies have less risk of developing a malignancy.
That being said, many rheumatologists will order a CT of the chest, abdomen, and pelvis at diagnosis to rule an occult malignancy. It’s also important to be up-to-date with routine cancer screening: colonoscopy, mammogram, etc.
How is myositis treated?
Typically the first medication we use are steroids. But these are just a band-aid and should not me used long-term. Like most autoimmune diseases, we use disease modifying anti-rheumatic drugs (DMARDs). There are many types of DMARDs. These can be used as monotherapy but also in combination with other DMARDs and also supportive treatments. For example, we can use mycophenolate mofetil, which is a DMARD, in combination with ambrisentan, which is a pulmonary hypertension medication. The specific type or regimen will depend on the manifestations, prior medical medications, and allergies.
The following are some the DMARDs used to treat myositis.
- Methotrexate
- Azathioprine
- Mycophenolate mofetil
- Hydroxychloroquine – for mild and mainly cutaneous cases
- Cyclosporine
- Tacrolimus
- IVIG
- Infliximab
- Rituximab
- Cyclophosphamide
- Repository corticotropin injection (Acthar gel)
How does one differentiate between myositis and steroid induced myopathy?
Sometimes people develop weakness when receiving large doses or steroids for prolonged periods of time, which often happens in people suffering from myositis. It can be difficult to differentiate between the two.
Typically, people with steroid myopathy have normal muscle enzymes meaning their CKs and aldolase are normal. People with myositis tend to have high muscle enzymes when they are flaring. If for some reason, it’s still unclear an MRI with STIR images can help identify active inflammation. A muscle biopsy is rarely necessary. People with steroid myopathy will also improve with decreasing steroid doses.
Conclusion
I hope this article was helpful and if you are interested in learning more about myositis please check out these sites.
Medical Disclaimer
This information is offered to educate the general public. The information posted on this website does not replace professional medical advice, but for general information purposes only. There is no Doctor – Patient relationship established. We strongly advised you to speak with your medical professional if you have questions concerning your symptoms, diagnosis and treatment.
References
- Rheumatology Secrets, 3rd edition
- Shinjo SK, Nascimento JJ, Marie SK. The effect of prior corticosteroid use in muscle biopsies from patients with dermatomyositis. Clin Exp Rheumatol. 2015 May-Jun;33(3):336-40. Epub 2015 Jan 29.