Secondary immunodeficiency common yet underdiagnosed and undertreated in HK

07 Jun 2022 bởiSarah Cheung
Secondary immunodeficiency common yet underdiagnosed and undertreated in HK

Local data presented at the 26th HKMF indicates that secondary immunodeficiency (SID), a common disease that can be treated with immunoglobulin (Ig) replacement therapy, is underdiagnosed and undertreated in Hong Kong.

SID is an immunodeficiency disorder that occurs in later life, with a prevalence about 30-fold higher than well-studied primary immunodeficiency (PID). [Front Immunol 2019;10:33] In contrast with genetic-associated PID, SID is caused by extrinsic factors, such as malignancy, pathogens, or use of biologics (ie, protein-based medications with immune-mediated effects). For example, rituximab is an anti-CD20 antibody depleting CD20-expressing B cells. Other common biologics associated with SID include blinatumomab, daratumumab and CD19 chimeric antigen receptor (CAR) T-cell therapy. [Hong Kong Bull Rheum Dis 2017;17:1-5; Front Immunol 2019;10:33]

“These extrinsic factors may suppress the immune system, leading to antibody deficiency and increased risk of severe infections,” said Dr Philip Li of the Department of Medicine, the University of Hong Kong, at HKMF. [Hong Kong Bull Rheum Dis 2017;17:1-5]

“However, SID is often underdiagnosed. Statistics from Queen Mary Hospital [QMH] showed that two-fifths of immunodeficiency patients have antibody deficiency, of whom only around one-third are diagnosed with SID,” reported Li. “However, these data may not be representative [ie, the incidence of SID may be underestimated] due to low awareness and vigilance of SID.”

“Underdiagnosis of SID may lead to undertreatment. In the past decade, [for example,] only 3 percent of local patients on rituximab received Ig replacement therapy, suggesting that only a small proportion of SID patients are diagnosed and treated,” said Li.

“In patients treated with immune cell–depleting agents, it is essential to closely monitor for signs and symptoms of SID. If necessary, referral to clinical immunologists should be considered for further assessment and management,” he advised.

“From this year, subcutaneous Ig [SCIg] therapy has become available for immunodeficiency as a special indication in the Hospital Authority,” he said.

SCIg is a home-based Ig replacement therapy for immunodeficiency, including SID. With the flexible dosing of SCIg, immunodeficiency patients can self-administer IgG according to their dosing schedule. Compared with conventional treatment with intravenous Ig (IVIg), which requires infusions of high antibody dose in the hospital setting, SCIg may provide additional benefits, including stable serum IgG levels and improved quality of life of patients. [Transfus Med Rev 2017;31:45-50]

Notably, SCIg is associated with a minimal risk of thromboembolic events, such as stroke and myocardial infarction, which could occur with IVIg. [Front Immunol 2018;9:1299; Front Immunol 2015;6:11] “[Due to the effectiveness and safety concerns,] SCIg is an optimal treatment choice for immunodeficiency patients, including those on IVIg, pregnant patients, and patients with a history of hypersensitivity reaction,” suggested Li.

“At QMH, an increasing number of patients were treated with SCIg between 2019 and 2021 [3 vs 13]. Some of these patients previously received IVIg. In our experience, SCIg-treated patients experienced low rates of adverse events and had high treatment satisfaction,” he concluded.