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This is systemic vasculitis (blood vessel inflammation) which occurs in the skin and the kidney.
It has an incidence of 20/100000 children per year. 90% are <10 years old, 50% <6 years old.
IgA antibodies deposit in the blood vessels leading to inflammation and vasculitis. There are variety of theories as to how this happens and HSP usually occurs after infection (especially after URTI) or use of certain drugs (see below).
- Previous infection (particularly upper respiratory tract infection)
- Certain drugs
- antibiotics:vancomycin, cefuroxime; ACE inhibitors: enalapril, captopril; diclofenac; ranitidine; and streptokinase
The classic triad of clinical features in HSP are purpura (100% of cases), joint pain (80%) and abdominal pain (60%). It is rare that these three symptoms are seen together in another condition.
The purpura is usually seen on the legs and the buttocks. The joint pain generally affect the ankles, knees and elbows but the hands and feet can be affected by arthritis as well.
About 40% of cases have kidney involvement. HSP involving the kidney causes haematuria and more than half have proteinuria which is important because this can develop into nephrotic syndrome in one-eighth of cases.
Diagnosis is generally clinical but there are some tests which can help.
- FBC - Platelets↑ (distinguishes from other causes of purpura)
- U+Es - Urea↑, creatinine↑ (shows kidney involvement)
- IgA levels↑
A skin biopsy can be done of the lesions where there is doubt about the diagnosis but this is not routinely done. A kidney biopsy may be done for diagnosis of kidney involvment or to assess the severity of the disease.
The management is symptomatic. Pain (joints and abdominal) is treated symptomatically and corticosteroids can be given early in the disease to reduce abdominal pain. With kidney involvement, depending on the level of kidney damage, different levels of steroid therapy are used. This can be oral or intravenous. Other drugs that can used are azathioprine (an immunosuppresant) and cyclophosphamide.
Usually, the disease is self-limiting and last 4 weeks. Kidney involvement needs to followed up for up to a year to make sure there is no permanent damage.