Systemic lupus erythematosus: SAQ

This girl has childhood-onset systemic lupus erythematosus. The combination of the malar rash sparing the nasolabial folds, painless oral ulcers, photosensitivity, a non-erosive symmetrical arthritis, autoimmune haemolytic anaemia with a positive direct antiglobulin test, thrombocytopenia, and lymphopenia, together with a strongly positive antinuclear antibody, high-titre anti-dsDNA, and low complement C3 and C4, is diagnostic of active multisystem lupus in an adolescent girl. The active urinary sediment with blood and protein mandates renal biopsy because the histological class of lupus nephritis determines the induction strategy. ^[1]

Question 1 (10 marks)

Outline the EULAR/ACR 2019 classification criteria for systemic lupus erythematosus and apply them to this patient. ^[1]

A complete answer states that the 2019 European League Against Rheumatism and American College of Rheumatism criteria are a weighted additive system. The mandatory entry criterion is a positive antinuclear antibody at any time, which this girl meets with a strongly positive titre of 1 in 1280. After the entry criterion is satisfied, weighted points are summed across clinical and immunological domains, and classification requires a cumulative score of 10 or more points, with each criterion counted once and the highest within a domain taken, and a more likely alternative explanation excluded. ^[1]

Applying the criteria to this patient: the malar rash is acute cutaneous lupus, scoring 6 points in the mucocutaneous domain; the joint pains reflect joint involvement, scoring 6 points in the musculoskeletal domain; the autoimmune haemolysis with a positive direct antiglobulin test scores 4 points in the haematological domain (the thrombocytopenia and lymphopenia also belong to this domain but only the highest, the haemolysis at 4, is counted); the low C3 and C4 together score 4 points in the complement subdomain; and the anti-dsDNA antibody scores 6 points in the SLE-specific antibody domain. The clinical and immunological contributions easily exceed the threshold of 10 points, confirming the classification. A candidate should also mention that the planned renal biopsy, if it shows class III or IV lupus nephritis, would classify lupus regardless of the point total via the biopsy shortcut. ^[1]

The candidate should briefly contrast the 2019 system with the older criteria: the 1997 American College of Rheumatology criteria require at least four of eleven criteria, and the Systemic Lupus International Collaborating Clinics 2012 criteria require at least four of seventeen criteria including at least one clinical and one immunological criterion. This demonstrates the expected familiarity with all three systems and their lineage. ^[2]