A 34 year old woman has fatigue, oral ulcers and a facial rash that is worse in the summer. She complains of having joint pains and stiffness especially in the morning. Urea and creatinine are slightly elevated with urinalysis demonstrating red cell casts. What is the SINGLE most appropriate investigations?
A. Ultrasound of the Kidneys, Ureters & Bladder
B. Joint aspiration
C. Autoantibodies
D. Intravenous urogram
E. Schirmer test
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. Given
in the options are autoantibodies which include anti-dsDNA titres.
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)