Comparison of clinical and radiological features of lung involvement between IgG4-related disease and idiopathic multicentric Castleman disease

<bold>Background:</bold> IgG4-related disease (IgG4-RD) and idiopathic multicentric Castleman disease (iMCD) have many overlaps in clinical, radiological, and pathological features. Moreover, the prognoses and treatments of the two diseases differ. So, the differential diagnosis of the two diseases is challenging and crucial for clinical management. However, there are few reports on the comparison between them, especially for patients with lung involvement. <bold>Aims:</bold> To clarify the clinical and radiological differences of lung involvement between IgG4-RD and iMCD. <bold>Method:</bold> Patients with IgG4-RD and patients with iMCD who exhibited lung involvement were enrolled. Clinical and chest CT findings on baseline were compared between them. <bold>Results:</bold> 178 patients with IgG4-RD and 61 patients with iMCD exhibited lung involvement. Patients with iMCD were younger (p<0.001) and had lower male-to-female ratio (p=0.004) than those with IgG4-RD. The levels of IgG, IgA, IgM, CRP, ESR and IL-6 were significantly higher in iMCD than those in IgG4-RD (all p<0.001). Although IgG4 levels were commonly elevated in both groups, it was significantly higher in IgG4-RD than that in iMCD (p<0.001). Nodular lesions were the most frequent findings in iMCD (98.4%), while the thickening of bronchovascular bundles was the most common findings in IgG4-RD (79.2%). Percentage of lung involvement of semi-quantitative assessment was significantly higher in iMCD than that in IgG4-RD (p<0.001). <bold>Conclusions:</bold> Compared to IgG4-RD, iMCD showed higher levels of inflammatory markers and immunoglobulin, and more extensive lung involvement, which indicated iMCD was a more aggressive condition than IgG4-RD.