Background/Purpose:

The goal of this study was to identify specific clinical features of patients with SLE who have inflammatory myositis.

Methods:

A retrospective chart review was performed of patients seen in the rheumatology clinic at a single center safety net hospital over a period of 4 months and who had an encounter diagnosis of SLE by ICD-10 code [M32.x]. Diagnosis of SLE was confirmed by one author (NB) using 2015 ACR/SLICC criteria. Cases of inflammatory myositis were defined by either muscle biopsy or with CK elevation/muscle weakness with or without confirming muscle MRI consistent with myositis. Data on patient demographics, clinical and laboratory features were extracted. Chi-square was used to analyze clinical features.

Results:

Of 354 patients with an encounter diagnosis of SLE, 30 (8.5%) were diagnosed with myositis. Most (93%) were women; 56% were African American and 43% Hispanic. Half were diagnosed with SLE and myositis simultaneously, 30% developed myositis after SLE diagnosis (mean 5.5 years later) and 20% were diagnosed with myositis prior to SLE (mean 10.9 years earlier). Patients fell into two clinical categories, those with features of systemic sclerosis (60%) and those without (40%). Among those with features of systemic sclerosis, 9 of 18 met the 2013 ACR/EULAR classification criteria for systemic sclerosis, while 9 of 18 did not but scored 5 or more criteria points.

SLE patients with co-existing features of systemic sclerosis were more likely to have Raynaud’s phenomenon and interstitial lung disease  (p<0.05) (Table 1 and 2). Muscle biopsy was performed in 16 patients, with 12 biopsies among 11 patients available for review (one patient underwent two biopsies over 3 years). Non-specific inflammatory changes were the most commonly observed muscle biopsy feature, followed by tubuloreticular inclusions by electron microscopy (Table 3). Autoimmune necrotizing myopathy was described in 4 of 12 muscle biopsies, three of whom lacked features of systemic sclerosis.

Conclusion:

In our cohort of SLE patients at a large safety net hospital, the diagnosis of co-existing myositis was seen in 8.5% of patients, most of whom had overlap features of systemic sclerosis.