Lupus
Formal Definition
Systemic Lupus Erythematosus (SLE); a multisystem autoimmune disease with immune complex deposition causing inflammation in virtually any organ; characterized by relapsing-remitting course, positive ANA (>95%), and specific antibodies (anti-dsDNA, anti-Smith); can affect joints, kidneys, CNS, heart, lungs, skin, and blood.
How It's Used on the Ward
"Lupus" or "SLE flare" — the great imitator that can look like almost any disease, famously associated with the malar butterfly rash.
Example
""22-year-old Black woman with arthralgias, malar rash, oral ulcers, pleuritis, proteinuria, leukopenia, and positive ANA: meets ACR criteria for SLE. Kidney biopsy showing diffuse proliferative glomerulonephritis (class III/IV) — starting hydroxychloroquine, high-dose prednisone, and mycophenolate for lupus nephritis.""
Clinical Context
2019 EULAR/ACR classification criteria: weighted point system. Anti-dsDNA and anti-Smith: highly specific for SLE (not sensitive). ANA positive in >95% but not specific (positive in 10–15% of healthy women). SLEDAI score tracks disease activity. Lupus nephritis: classified by biopsy (ISN/RPS classes I–VI); class III/IV most severe, requires immunosuppression. CNS lupus: seizures, psychosis, myelitis. Antiphospholipid antibody syndrome (APS): thrombosis + pregnancy loss; treat with anticoagulation. Hydroxychloroquine is backbone therapy for all lupus — reduces flares, protects kidneys, lowers mortality. Avoid sun exposure (UV triggers flares). Drug-induced lupus: hydralazine, procainamide, isoniazid — anti-histone antibodies positive.