Investigations should be directed by accurate historical and clinical findings. Many cases are from a drug reaction, and removal of the drug allows resolution. However, a vasculitis rash may herald a serious underlying condition.
- Most vasculitic rashes are caused by small vessel vasculitis.
- Many cases are related to a new medication – e.g. beta-lactam antibiotics, sulfonamides, allopurinol, phenytoin.
- Infectious causes of a vasculitis must be excluded.
- Urinalysis should always be obtained; if normal, concomitant renal vasculitis is unlikely.
- Histological confirmation by skin biopsy is desirable.