• Clinical science

Henoch-Schonlein purpura (Anaphylactoid purpura…)


Henoch-Schonlein purpura (HSP) is an acute immune complex-mediated small vessel vasculitis that most commonly occurs in children. It is often preceded by an upper respiratory tract infection and typically presents with a tetrad of symptoms: palpable purpura, arthritis/arthralgia, abdominal pain, and renal disease. However, in any individual patient, only some of the classic tetrad of symptoms may be present. HSP is a clinical diagnosis, but in particularly unclear or atypical cases a biopsy may be used to confirm the diagnosis. Because the disease course is usually self-limiting, treatment is generally supportive. Severe cases may require glucocorticoids, antihypertensive drugs, and possibly dialysis. HSP has an excellent prognosis, usually resolving within one month when not complicated by significant renal disease.


  • Sex: >
  • More common in children
    • 90% of cases < 10 years old
    • Peak incidence: 6 years


Epidemiological data refers to the US, unless otherwise specified.


  • The exact pathogenesis is unknown and assumed to be multifactorial. Factors that likely play a role include:
    • Preceding infection
      • > 75% of cases preceded by viral or bacterial infection 1–3 weeks prior
      • Most commonly an upper respiratory tract infection caused by group A streptococcus
      • GI infections also possible; many other organisms have also been associated with HSP
    • Genetic predisposition
    • Drugs (e.g., some antibiotics and antiarrhythmics) and vaccinations (e.g., yellow fever, cholera)



  • Hypothesized pathophysiological mechanism: exposure to allergen/antigen (e.g., infection, drugs) → stimulation of IgA production → deposition of IgA immune complexes in vascular walls (e.g., in the skin, GI tract, joints, kidneys) → activation of complement → vascular inflammation and damage


Clinical features


  • Symptom onset often 1–3 weeks after an infection, typically affecting the upper respiratory tract


  • Skin (∼ 100% of cases)
    • Symmetrically distributed, raised, erythematous macules or urticarial lesions that coalesce into palpable purpura (non-blanching skin lesions)
    • Most common sites: the lower extremities, buttocks, and other areas of pressure or constraint (e.g., from socks or clothing)
  • Joints (∼ 75% of cases): : arthritis/arthralgia, most common in the ankles and knees
  • Gastrointestinal tract (∼ 60% of cases)
  • Kidneys (∼ 50% of cases): HSP nephritis with signs and symptoms of nephritic syndrome
  • Other organs
    • Scrotum (e.g., scrotal swelling, pain, and tenderness)
    • Central and peripheral nervous system (e.g., headaches, seizures, focal neurologic deficits, ataxia, intracerebral hemorrhage, central and peripheral neuropathy)
    • Respiratory tract (e.g., mild interstitial changes, pulmonary hemorrhage)

HSP is characterized by a tetrad of clinical findings: palpable purpura, arthritis/arthralgia, GI symptoms, and renal disease
HSP is one of the important differential diagnoses to consider in cases of pediatric limp!



HSP is a clinical diagnosis; , laboratory tests are not essential to HSP diagnosis. However, they may be useful for excluding differential diagnoses in patients exhibiting only one or two of the HSP tetrad of symptoms, as is often the case in the first few days. Laboratory tests are also useful for monitoring the extent of renal involvement, which helps determine the prognosis. Definitive diagnosis in uncertain cases is made via biopsy.

Laboratory tests

The platelet count in HSP is normal or elevated, as opposed to other causes of purpura!


  • Indication: performed in patients with marked abdominal symptoms or suspected complications
  • Abdominal ultrasound/CT


  • Indications: reserved for patients with unusual skin presentations or severe renal involvement (e.g., persistent nephrotic syndrome)
  • Skin: Leukocytoclastic vasculitis with IgA and C3 immune complex deposition (hallmark) in small vessels of the superficial dermis
  • Kidney
    • Renal involvement characterized by mesangial IgA deposition; C3 and fibrin are also frequently present.
    • Crescent formation in more severe cases


Differential diagnoses

HSP is a unique cause of purpura without thrombocytopenia!



  • Autoimmune diseases : no IgA deposition on biopsy and associated with specific antibodies
  • Septic arthritis: arthritis typically in a single joint
  • Reactive arthritis: no rash, abdominal pain, or renal symptoms

Renal disease


The differential diagnoses listed here are not exhaustive.


Most cases of HSP are self-limiting and only require supportive care; (e.g., pain management) with regular outpatient follow-up. Severe HSP requires hospitalization and intensive medical therapy.

Mild disease

  • Outpatient treatment
  • Usually no treatment necessary
  • NSAIDs for pain management, rest, and adequate hydration

Severe disease




We list the most important complications. The selection is not exhaustive.