Systemic Lupus Erythematosus Disease Background

Introduction 

Systemic lupus erythematosus (SLE) is a chronic, multisystem, inflammatory, autoimmune disorder characterized by the formation of autoantibodies directed against self-antigens and immune-complex formation. It has a relapsing and remitting disease course with organ damage resulting from persistent disease activity and therapy. It can be diagnosed with a single organ involvement such as lupus nephritis.

Epidemiology 

Systemic lupus erythematosus is predominantly diagnosed in females of childbearing age with a female-to-male ratio of 9:1. The incidence and prevalence rates differ worldwide with systemic lupus erythematosus more frequently occurring in Asian, African, Caribbean, and Hispanic individuals. In the Asia-Pacific region, the incidence ranged from 0.9 to 8.4 and the prevalence ranged from 3.7 to 127 per 100,000 population.

In Mainland China, the prevalence was 30 to 70 per 100,000 population in 2008 based on a large epidemiological study, whereas in Hong Kong, the prevalence was estimated to be 0.1% of the general population with an incidence of 6.7 per 100,000 population. A nationwide population-based study from 2005 to 2015 which utilized the National Health Insurance database in South Korea reported that the average prevalence of the disease was 28 per 100,000 person-years and the average incidence was 3.7 per 100,000 person-years.

Asian patients with systemic lupus erythematosus tend to have a higher disease activity, more severe disease, more organ damage, and higher incidence of renal involvement. Asian patients less commonly develop systemic lupus erythematosus-related antiphospholipid syndrome and venous thrombosis.

Pathophysiology 

The interplay between genetic and environmental factors activates the patient's innate and adaptive immunity resulting in immunologic alterations. Genetically susceptible individuals lose their immune tolerance upon exposure to environmental factors (eg cigarette smoke, silica, Epstein-Barr virus infection, ultraviolet B [UVB] radiation, oral contraceptives, or drugs [eg Procainamide, Hydralazine, Isoniazid, Minocycline, tumor necrosis factor-α inhibitors]) resulting to the irregular activation of autoimmunity. 

This leads to the production of autoantibodies, formation of immune complexes, production of autoreactive T cells and B cells, activation of complement, and release of cytokines causing tissue damage which may be limited to an organ or can cause systemic involvement leading to significant morbidity and mortality.

Classification 

Categories of Disease Activity in Systemic Lupus Erythematosus

Mild disease activity is considered in patients with the following:

• Constitutional symptoms, fatigue, mouth ulcers, mild arthritis, or a rash that is ≤9% of the body surface area (BSA)
• Disease is clinically stable without life-threatening organ involvement
• Platelet count of 50-100 x 10³/mm³
• Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) of ≤6
• British Isles Lupus Assessment Group (BILAG) C or ≤1 BILAG B manifestation

• Rheumatoid arthritis-like arthritis, serositis, rash that is 9-18% of the BSA, cutaneous vasculitis that is ≤18% of the BSA
• Platelet count 20-50 x 10³/mm³
• SLEDAI of 7-12
• ≥2 BILAG B manifestations

• Major organ- or life-threatening disease (eg cerebritis, mesenteric vasculitis, myelitis, nephritis, pneumonitis, pericarditis, thrombotic thrombocytopenic purpura-like disease, acute hemophagocytic syndrome)
• Platelet count <20 x 10³/mm³
• SLEDAI of >12
•  ≥1 BILAG A manifestations