A 32 year old woman has malaise, fatigue, weight loss and fever. On examination, a
Malar rash with sparing of nasolabial fold can be seen. She also complains of joint
stiffness and pain. What is the SINGLE most appropriate investigation?
A. Anti-dsDNA
B. Anti-histone
C. Anti-centromere
D. Anti-Jo-1
E. Anti-Scl-70
The signs and symptoms here point towards systemic lupus erythematosus (SLE). The 3
best initial test to order are anti-dsDNA titre, complement (C3 and C4) and ESR.
Systemic lupus erythematosus (SLE)
Important must know features for the PLAB exam
- Remitting and relapsing illness
- Mouth ulcers → large, multiple and painful
- Lymphadenopathy
- Malar (butterfly) rash: spares nasolabial folds
- Discoid rash: scaly, erythematous, well demarcated rash in sun-exposed areas
- Photosensitivity
- Arthralgia
- Raynaud’s phenomenon occurs in about one fifth of patients but is often mild
Cardiovascular: pericarditis - Respiratory: pleurisy, fibrosing alveolitis
- Renal: Glomerulonephritis (nephritis is often asymptomatic and is detected by
proteinuria, haematuria, hypertension or a raised serum urea or creatinine) - Neuropsychiatric: anxiety and depression are common
Investigation
FBC and ESR: - Mild normochromic normocytic anaemia is common
- ESR is raised
Autoantibodies: - Antinuclear antibody (ANA)
o Screening test with a sensitivity of 95% but not diagnostic in the
absence of clinical features. It is a nonspecific antibody that is also
present in many patients with systemic autoimmune conditions - Anti-dsDNA
o Highly specific (> 99%), but less sensitive (70%) - Anti-Smith
o Most specific (> 99%), but even less sensitive (30%-40%) - Anti-histone: drug-induced lupus ANA antibodies are often this type
- 20% are rheumatoid factor positive
Complement levels (C3, C4) are low during active disease (formation of complexes leads
to consumption of complement)