Inflammatory myositis in systemic lupus erythematosus

Area of Science:

• Rheumatology
• Immunology
• Internal Medicine

Background:

• The co-occurrence of inflammatory myositis within systemic lupus erythematosus (SLE) requires further investigation.
• Understanding the incidence, types, and risk factors of myositis in SLE patients is crucial.

Purpose of the Study:

• To determine the incidence of inflammatory myositis in a cohort of pediatric and adult SLE patients.
• To identify distinct types of inflammatory myositis and associated risk factors in SLE.
• To describe clinical, laboratory, and pathological features of myositis in SLE.

Main Methods:

• Retrospective analysis of SLE patients diagnosed with myositis between 2010-2019.
• Inclusion of data from two pediatric and one adult hospital.
• Collection and descriptive statistical analysis of demographic, clinical, laboratory, and pathological features.

Main Results:

• 6.3% of 1718 SLE patients (108 individuals) had coexisting inflammatory myositis.
• Higher prevalence observed in Black individuals and those with childhood-onset SLE.
• Concurrent onset of SLE and myositis occurred in 68%; common features included systemic sclerosis overlap (48%), dermatomyositis rashes (33%), arthralgias/arthritis (>90%), and thrombotic events/pregnancy morbidity (>33%).
• Frequent laboratory findings included lymphopenia, hypocomplementemia, and positive RNP antibodies.
• Myositis-specific antibodies (MSA) and myositis-associated antibodies (MAA) were present in over 40% of patients.
• Muscle biopsy revealed diverse pathology, including nonspecific changes, dermatomyositis, polymyositis, and necrotizing autoimmune myopathy.

Conclusions:

• Inflammatory myositis is a significant comorbidity in 6.3% of SLE patients.
• Clinical manifestations like dermatomyositis rashes, systemic sclerosis overlap, arthralgias/arthritis, and cytopenias are common.
• Elevated frequency of RNP, MSA, and MAA supports their role in SLE-myositis.
• Black individuals and those with childhood-onset SLE exhibit higher myositis prevalence.
• Routine myositis screening is advised for Black SLE patients, childhood-onset SLE, and those with MSA/MAA.