Discussion

IgG4-RD is recognised for its potential to affect nearly every organ, particularly a preference for large and medium-sized arteries when vascular involvement occurs.2 The aorta is the most commonly affected artery followed by the iliac and coronary arteries.3 4 However, instances of splenic artery aneurysms are exceedingly rare with only two cases reported in the literature. We have summarised the characteristics of the three patients we reported along with the two patients previously reported in table 1. During the follow-up time between the initial diagnosis and the identification of the splenic artery, these three patients underwent one to two abdomen CT scans annually, none of which revealed splenic artery aneurysm formation. The three patients we reported had normal or not significantly elevated serum IgG4 levels and no arterial involvement was found in these three patients at the time of diagnosis. Moreover, other organ involvement was stable when the splenic artery aneurysm was detected. It is noteworthy that all five patients had salivary gland involvement and only one patient had other arterial involvement indicating that splenic artery involvement and other arterial involvement are not parallel in IgG4-RD. All these patients had an IgG4-RD RI of no more than 5 suggesting that splenic artery aneurysm may not indicate disease flare. However, aneurysms may represent a form of damage rather than an active disease. These aneurysms likely represent a late complication of prior vascular involvement that may not have been detected clinically during active disease. Figure 1c shows an aneurysm that developed calcification whereas cases 1 and 2 show no signs of calcification. On one hand, neither case 1 nor case 2 suffered from any chronic illnesses such as diabetes, hypertension or hyperlipidaemia that might damage the arteries. On the other hand, they abstain from alcohol and smoking.

Considering the risks associated with biopsy, tissue biopsy of the splenic artery aneurysm was not performed in our three patients. It is not certain whether this is a coincidence. Indeed, vascular involvement in IgG4-RD is usually lesions presenting as periarteritis. However, the periarteritis may have been improved when the artery aneurysm formed. One previously reported patient underwent a biopsy and was found to have mild-to-moderate infiltration of plasma cells and lymphocytes in the wall of the splenic artery aneurysm with a maximal plasma cell IgG4+/IgG+ ratio of 40%.5 Therefore, we hypothesise that the observed aneurysms are probably linked to IgG4-RD. Two out of the three patients we reported underwent embolisation of the splenic artery aneurysm. The follow-up time for the three patients was 7, 12 and 20 months, respectively. The splenic artery aneurysm remained stable with no signs of progression. Currently, the mechanism of vascular involvement in patients with IgG4-RD remains unclear. Notably, a recent study demonstrates elevated absolute T-helper 1 (Th1) cells counts in individuals with IgG4-RD compared with healthy controls.6 It is interesting to note that Th1 cells typically trigger inflammatory cellular reactions such as macrophage activation which has a direct impact on the development of abdominal aortic aneurysms.7 The cases we reported here highlight a potential association between IgG4-RD and concurrent splenic artery aneurysms. However, further research is required to elucidate a more comprehensive empirical and theoretical basis for the clinical diagnosis and management of IgG4-RD with splenic artery aneurysms.