Rheumatoid pulmonary nodules. Clinical and imaging features compared with malignancy

The objective of this study was to identify clinical and imaging features that distinguish rheumatoid lung nodules from malignancy. We conducted a retrospective review of 73 rheumatoid patients with histologically-proven rheumatoid and malignant lung nodules encountered at Mayo Clinic, Rochester, MN (2001-2016). Medical records and imaging were reviewed including a retrospective blinded review of CT and PET/CT studies. The study cohort had a mean age of 67 $\pm$ 11 years (range 45-86) including 44 (60%) women, 82% with a smoking history, 38% with subcutaneous rheumatoid nodules, and 78% with rheumatoid factor seropositivity. Subjects with rheumatoid lung nodules compared to malignancy were younger (59 $\pm$ 12 vs 71 $\pm$ 9 years, p $<$ 0.001), more likely to manifest subcutaneous rheumatoid nodules (73% vs 20%, p $<$ 0.001) and rheumatoid factor seropositivity (93% vs 68%, p = 0.034) but a history of smoking was common in both groups (p = 0.36). CT features more commonly associated with rheumatoid lung nodules compared to malignancy included multiplicity, smooth border, cavitation, satellite nodules, pleural contact, and a subpleural rind of soft tissue. Optimal sensitivity (77%) and specificity (92%) (AUC 0.85, CI 0.75-0.94) for rheumatoid lung nodule were obtained with $\ge$ 3 CT findings ($\ge$ 4 nodules, peripheral location, cavitation, satellite nodules, smooth border, and subpleural rind). Key ${}^{18}$FDG-PET/CT features included low-level metabolism (SUV${}_{max}$ 2.7 $\pm$ 2 vs 7.2 $\pm$ 4.8, p = 0.007) and lack of ${}^{18}$F-fluorodeoxyglucose (FDG)-avid draining lymph nodes. Rheumatoid lung nodules have distinct CT and PET/CT features compared to malignancy. Patients with rheumatoid lung nodules are younger and more likely to manifest subcutaneous rheumatoid nodules and seropositivity. (orig.)