Dr. Nothem discussed an interesting case of a patient presenting in severe respiratory failure who was ultimately diagnosed with polymyositis.
What is polymyositis?
Polymyositis (PM) is one of three idiopathic inflammatory myopathies (IIMs), the other two being dermatomyositis (DM) and inclusion body myositis (IBM). These three diseases are characterized by autoimmunity and inflammatory involvement of muscle fibers resulting in muscle weakness.
How does it present?
PM classically presents with muscle weakness, but can also have systemic symptoms (fever, fatigue, weight loss), arthritis, or Raynaud's.
Muscle involvement typically presents as progressive symptoms over months. This should be symmetric and proximal, with objective muscle weakness. Patients often report difficulty climbing stairs, brushing hair, etc.
1/3 of patients with PM or DM present with what is called the antisynthetase syndrome: this is an acute onset of significant constitutional symptoms as well as the positive autoantibodies (such as anti–Jo-1) plus two of the following clinical features:
Inflammatory myositis
Interstitial lung disease
Raynaud phenomenon
Nonerosive inflammatory arthritis
Mechanic's hands
The presence of ILD is uncommon, but happens in about 10% of patients, with nonspecific interstitial pneumonitis being the most common form.
GI involvement can be seen, because the striated muscle (found in the upper 2/3rds of the esophagus) can be involved. Patients typically complain of dysphagia and associated symptoms; they also have an increased risk of aspiration pneumonia.
Symptomatic cardiac involvement is uncommon, but can include pericardial involvement, ACS, or conduction delays. The skin is generally not involved in PM.
What labs would I see?
CK should be elevated, indicating muscle breakdown.
+ ANA is seen in about 80% of patients
Ro-52 auto-antibodies can be positive: these are associated with ILD.
Anti-Jo-1, anti-SRP can also be positive
The gold standard for diagnosis is muscle biopsy: this should be obtained initially in most patients to distinguish between DM, PM, and IBM as well as other myopathic disorders.
How do I treat PM?
Steroids are first-line: steroids should be started quickly and at high-doses until muscle enzymes normalize. Methotrexate or azathioprine can be used for either glucocorticoid-resistant disease or as glucocorticoid sparing agent. These are also used in poor prognosis groups and patients with extramuscular disease such as ILD. Don't forget supportive therapies (PT & OT) to help these patients recover.
What else do I need to consider?
There is an increased rate of malignancy in patients with both DM and PM. (Relative risk for malignancy is 2.4 to 7.7 for DM and 1.7 to 2.1 for PM, compared with the general population.) The risk of malignancy is highest in the first year after diagnosis, but remains elevated. Age-appropriate cancer screens are needed in all patients with this diagnosis. Because of the association with ovarian cancer, consider specific screening for ovarian cancer (i.e. transvaginal pelvic ultrasonography.)
References
1. MKSAP 17.
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