Learn to recognize myositis and myopathy (aka the idiopathic inflammatory myopathies), perform the appropriate initial testing, whether or not statins and exercise are safe to continue, and how to partner with our subspecialist colleagues to treat these patients in primary care. Recorded LIVE at Johns Hopkins, we’re joined by Dr. Lisa Christopher-Stine, @DrLisaCS of @HopkinsMedicine, a rheumatologist and leading expert on myositis and myopathy!
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“If you don’t like the sound of a future project six months from now, then it won’t sound any better in six months.” –Dr. Lisa Christopher-Stine
Myositis is commonly referred to as Idiopathic Inflammatory Myopathy (IIM). The IIMs are a heterogeneous group of rare autoimmune disorders with varying combinations of muscle weakness and extramuscular manifestations like skin involvement, arthritis, and interstitial lung disease (Lundberg 2021). Myositis-specific auto-antibodies (MSAs) are associated with specific clinical phenotypes. Further, since MSAs are present in up to 60 percent of patients with IIM they can help predict organ involvement and prognosis (Lundberg 2021).
Classically, we were taught to split the IIMs into polymyositis (PM) and dermatomyositis (DM) based on the presence of skin involvement. More recently, it’s become apparent that the IIMs can be split into the “clinico-serological subtypes” of DM, antisynthetase syndrome (AS), overlap myositis (OM), immune mediated necrotizing myopathy (IMNM), and inclusion body myositis (Khadilkar 2020).
Dr. Christopher-Stine points out that myositis usually has a subacute onset and many patients incorrectly attribute their symptoms to aging. Fatigue and difficulty rising from deep-seated chairs are common complaints (Christopher-Stine UpToDate 2022). She asks questions like, “If there was a fire in a crowded theater, could you get out of your seat to run away from the fire?” to differentiate true weakness from fatigue. Classically, myopathy is painless, but pain can accompany weakness in inflammatory myopathies (Lundberg 2021). However, Dr. Christopher-Stine points out that pain WITHOUT weakness is highly atypical (expert opinion).
Ask about rashes (especially of the eyelids, MCP, and PIP joints), fevers, weight loss, and new onset Raynaud’s phenomenon. Pruritis or burning pain of the scalp can be present in myositis (Christopher-Stine UpToDate 2022). She points out that rashes may appear hyperpigmented rather than erythematous in darker skin tones (Skin of Color Society, resources).
Overt cardiac involvement is uncommon (but may be subclinical), so be sure to ask about signs and symptoms of cardiopulmonary disease.
Dr. Christopher-Stine recommends we examine the neck and hip flexors with the patient in the supine position to prevent recruitment that can mask true weakness (expert opinion). Apply resistance distal to the joint of interest and proximal to the next joint (e.g., place hand just above the knee to test hip flexion). Test the hip extensors with the patient lying prone. Place a hand on the forehead to gently resist neck flexion and test for weakness out of proportion to neck extension (Christopher-Stine. Clinical Manifestation of DM. UpToDate 2022).
You have been testing grip strength wrong! The forearm flexors are a common distal muscle group affected by inclusion body myositis (Vencovsky 2019). Ask the patient to flex at the PIP and DIP joints, but not the MCPs. This prevents contribution from intrinsic hand muscles and can detect the subtle weakness of the forearm flexors (e.g., as found in inclusion body myositis).
Look for the shawl sign on the neck and chest, along with plaques, or patches on any extensor surfaces. We use the term Gottron’s sign for flat lesions and Gottron’s papules if raised. Curiously, the gun holster sign, increased pigmentation of the lateral thighs, may be present in dermatomyositis (Lundberg 2021). As noted above, the rash in dermatomyositis is often itchy, especially on the scalp, and may be accompanied by a burning sensation.
This list is not all-inclusive (Christopher-Stine. DDx of DM and PM. UpToDate 2022).
Specific differential considerations for dermatomyositis (DM) include:
Dr. Christopher-Stine recommends consideration of the following tests when working up a patient with suspected or confirmed myositis (Christopher-Stine, UpToDate 2022).
Notably, renal disease is uncommon, so a urinalysis is not a standard order.
The following studies are often ordered by specialists to further characterize a patient’s disease for treatment options and prognosis.
Most idiopathic inflammatory myopathies (excluding inclusion body myositis and anti-synthetase syndrome) carry an increased risk for malignancy, especially dermatomyositis (Lundberg 2021). This risk seems highest in the first year after diagnosis (Chen 2010, Targoff. Malignancy in DM and PM. UpToDate 2022). In her practice Dr. Christopher-Stine screens with an initial CT abdomen and pelvis for all patients with DM, but she admits this is not standard everywhere.
Consider the following cancer for screening in patients with myositis:
Evidence indicates that exercise is safe and may improve muscle function and quality of life for patients with myositis (Alexanderson 2018; de Oliveira 2018, Lundberg 2021). It should be started with a gradual progression (Lundberg 2021). Dr. Christopher-Stine recommends light resistance training or cardio rather than heavy weights. Patients can self-titrate based on results.
Dr. Christopher-Stine offers that statins are generally beneficial and safe medications. Small retrospective studies suggest that patients with myositis (excluding statin-associated autoimmune myositis –more on this below) can safely take a statin if indicated (Pires Borges 2019, Bae 2020). For these patients start low and go slow (e.g., Mon, Wed, Fri). Then, titrate based on tolerance and lipid goals as you would for any patient requiring a statin (expert opinion).
Atorvastatin can be a direct myotoxin (symptoms of myalgia or rhabdomyolysis) or trigger an immune-mediated necrotizing myositis (typically presents after three years of statin exposure) —Troyanov 2017, Lundberg 2021. HMGCR antibodies (HMG-CoA Reductase) are widely available, sensitive, and specific (Mammen 2012).
No consensus guidelines or FDA approved therapies exist related to the rarity of diagnosis and heterogeneity amongst the idiopathic inflammatory myopathies. Treatment generally consists of corticosteroids in combination with steroid sparing agents (e.g., methotrexate), biologic agents (e.g., rituximab), anti-TNF agents, and IVIG (Lundberg 2021).
Listeners will develop a framework for the diagnosis and management of myositis
After listening to this episode listeners will…
Dr. Christopher-Stine has received consulting fees, honoraria, and worked in advisory roles to Janssen, Boehringer-Ingelheim, Mallinckrodt, EMD Serono, Roivant/Priovant, Pfizer, ArgenX, Horizon Therapeutics, and Allogene. She has intellectual property interest and receives royalties from Inova diagnostics for the anti-HMGCR antibody testing assay, which she helped discover in 2009 with her group at Johns Hopkins.
The Curbsiders report no relevant financial disclosures.
Watto MF, Christopher-Stine L, Williams PN. “#349 Myositis and Myopathy, Live!”. The Curbsiders Internal Medicine Podcast. http://thecurbsiders.com/episode-list Final publishing date August 1, 2022.
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