Differentials
Infective endocarditis
SIGNS / SYMPTOMS
Increased risk if known underlying valvular disease or high-risk behaviour, such as intravenous drug use.
INVESTIGATIONS
Three paired blood cultures (aerobic and anaerobic) to detect causative organism. Previous antibiotic exposure decreases the yield.
Keep blood cultures long enough to exclude HACEK organisms (Haemophilus aphrophilus and Haemophilus paraphrophilus, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella kingae), although these are not specifically associated with vascular complications.
Echocardiocardiography shows valvular vegetations.
Hypercoagulability syndromes
SIGNS / SYMPTOMS
Absence of chronic B-type symptoms, such as fevers, weight loss, myalgias, and arthralgias.
INVESTIGATIONS
Difficult to assess after anticoagulation therapy has started.
Heterozygous factor V Leiden and prothrombin mutations (which can be diagnosed through genetic testing) are common and generally not severe enough to mimic vasculitis.
It is important to rule out the antiphospholipid antibody syndrome by looking for anticardiolipin antibodies or a prolonged dilute Russell viper venom time.
Systemic lupus erythematosus (SLE)
SIGNS / SYMPTOMS
Only rarely associated with a true vasculitis, but, as with the primary systemic vasculitides, it can affect multiple organ systems simultaneously.
The cutaneous manifestations of SLE, such as a malar rash and discoid lesions, are readily differentiated from the palpable purpura that is found with vasculitis.
INVESTIGATIONS
Positive anti-nuclear antibody test, and other lupus specific antibodies (e.g. DNA, Smith).
Direct immunofluorescence of biopsied tissue will demonstrate a 'full house' pattern, characterised by deposition of multiple types of immunoglobulins and complement.
Levamisole-induced vasculitis
SIGNS / SYMPTOMS
Distinctive, purple or ulcerating lesions on the ears and the extremities.
INVESTIGATIONS
Proteinase 3 anti-neutrophil cytoplasmic auto-antibody (PR3-ANCA)-positive, often at high titres, but urine toxicology (or history) should establish history of cocaine use.
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