Rationale: Myositis-related ILD are a heterogenous group of disorders. Clinical features and presence of autoantibodies determines sub-type with prognostic implications. The aim of this study was to assess how quantitative radiology scores correlated with phenotype.
 
Methods: Retrospective clinical, radiological, serological and therapeutic data was analysed for all myositis-related ILD patients. Semi-quantitative assessment of fibrosis on CT was performed using validated methodology.
 
Results: 14 patients with myositis-related ILD were assessed. Median age at diagnosis was 51.5 yrs, with 64% females. Despite having signs and symptoms consistent with myositis, 21.4% of patients had undetectable auto-antibodies. Reticulation was the most common radiological finding with mean lung involvement of 8% (range:0%-33%), followed by pure ground glass (mean:6.4%; range:0-23%), then honeycombing (mean:1.6%; range 0%-20%).  Patients with predominantly lower lobe disease had lower mean % predicted FVC (71+-22% v 92+-16.3%, p=ns) and DLCO (54+-20% v 67+-13%, p=ns) than those with upper lobe disease and were less likely to have a decline in FVC over time. Percentage of lung volume affected by reticulation correlated with DLCO (R²=0.6218)
 
Conclusion: The pattern of interstitial fibrosis is variable in myositis-related ILD. Lower zone predominant disease is more common but is not associated with worse prognosis. The proportion of reticulation appears to correlate with DLCO.  Notably honeycombing does not but is an uncommon feature.