EUH Morning Report: What are the important clinical features for diagnosing the different types of inflammatory myopathies?

The Bottom Line: “Idiopathic inflammatory myopathy (IIM) includes dermatomyositis (DM), polymyositis (PM), overlap myositis (OM), sporadic inclusion body myositis (IBM) and necrotising autoimmune myopathy (NAM), also known as immune-mediated necrotising myopathy. DM, OM and NAM all present similarly, with proximal weakness and elevated creatine kinase (CK) level. By contrast, IBM preferentially involves the long finger flexors and quadriceps, and presents with a normal or only mildly elevated CK. Developments in serological testing and imaging are shifting the diagnostic paradigm away from a reliance on histopathology.” (Ashton)

“There is some debate as to whether PM exists as a discrete entity, or is an ill-defined condition encompassing connective tissue disease (CTD) associated myositis, or OM, and the previously poorly recognised NAM” (Ashton)

(Greenberg & Amato)

“Epidemiologic studies suggest that the incidence of IM grouped together is >4 cases per 100,000 with prevalence in the range of 14–32 per 100,000. Defining the actual incidence and prevalence of the individual myositides is limited, however, by the different diagnostic criteria employed in various epidemiologic studies, increasing recognition of AS, and frequent misdiagnosis of IBM and IMNM. Idiopathic PM without signs of an overlap syndrome is quite rare, while DM, IBM, and IMNM occur in roughly similar frequencies. DM can occur in children (juvenile DM), while IBM always occurs in adults and is the most common cause of myopathy in those aged >50. DM, PM, and AS are more common in women, while IBM is more common in men.” (Greenberg & Amato)

Midtown Morning Report: What is the pathophysiology of statin-associated myopathy?

The Bottom Line: “The pathophysiology of statin-associated autoimmune myopathy (SAAM) is not clear but is likely related to statin-induced autoimmunity against HMG-CoA reductase in genetically susceptible individuals.” (Nemati)

EUH Morning Report: At what dosage and duration can corticosteroid induced myopathy develop? What are the risk factors?

The Bottom Line:

• It typically develops with doses >10 mg prednisone equivalents/day used for four weeks or longer.
• 2-3 weeks of higher doses (such as 40 to 60 mg prednisone/day) have been associated with more acute presentations.
• At higher risk:
  • Elderly patients (due to lower baseline muscle mass)
  • Oncology patients
  • Women (mechanism of this is unclear)
  • Prior muscle disease or spinal cord injury
  • Chronic respiratory illness
  • Poor nutritional status and/or sedentary lifestyle
• Acute corticosteroid myopathy (ASM) is rare, but can develop 14 days of initiating of treatment. (It is characterized by unpredictability and heterogeneity, sometimes developing within 1–3 days, after a single dose, which may not be high and administered by varied routes.)

EUH Morning Report: What are characteristics of antisynthetase syndrome and do they include gastrointestinal manifestations?

The Bottom Line:

Suspect antisynthetase syndrome in patients with consistent clinical presentation, including ≥1 of:

• interstitial lung disease (particularly if idiopathic) or unexplained acute respiratory distress syndrome
• idiopathic inflammatory myopathy
• arthritis (generally nonerosive)
• Raynaud phenomenon
• fever of unknown origin
• mechanic’s hands – hyperkeratotic skin over palmar surface and fingers