A previously healthy 8-year-old boy presented with 2 days of knee and ankle pain with no known cause. His parents denied that he had any trauma or fever. On physical examination, he was afebrile in no apparent distress. His left knee was swollen and tender (Figure 175-1). He admitted to other joint pains but there was no swelling or tenderness in the other joints. The pediatrician noted a petechial and purpuric eruption from his buttocks down to his ankles (Figure 175-1). It was non-blanching but only barely palpable. There were prominent circumferential petechiae around the left sock area. Upon further questioning, the mother admitted that her son had a viral upper respiratory infection 2 weeks ago. A urinalysis showed mild hematuria but no proteinuria. He never developed abdominal pain. Therapy was supportive and systemic corticosteroids were not used.

Henoch-Schonlein Purpura (HSP) is a small vessel vasculitis characterized in children by a classic, palpable, purpuric rash over the lower extremities. In addition to the rash, children may also exhibit arthralgias, hematuria, and abdominal pain. The exact disease trigger is unknown; however, the symptoms of HSP are attributed to IgA deposition in the systemic vasculature. Though a minority of patients may develop long-term renal complications, the majority of cases are self-limited.

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  In the early 20^th century, HSP was thought to be due to anaphylaxis. Consequently, the disease was named “anaphylactoid purpura.” Occasionally, this term may still be used in reference to HSP.¹

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  HSP is the most common vasculitis in the pediatric population.²

  
  
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  Although HSP may affect all age groups, it is most common between children ages 2 to 6 years old.^2–4

  
  
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  The disease affects an estimated 70.3 per 100,000 children per year.^2,3

  
  
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  A very slight male predominance exists with a 1.2:1 male to female ratio.^2,3

  
  
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  White children have a much higher incidence compared to black children.^2,3

  
  
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  Though the incidence has been reported to be about 100 times greater in children than adults, HSP is typically less severe in the pediatric population.⁵

  
  
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  The peak disease occurrence is in the fall and winter months.¹

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  HSP is an immune complex-mediated disease.²

  
  
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  Clinical symptoms are due to widespread IgA deposits in the small vessels of the GI tract, renal glomeruli, and skin.^1,4 IgA activates a local inflammatory response which leads to necrosis of the blood vessels.²

  
  
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  IgA may bind to endothelial cells of the vasculature and lead to the destruction of these cells by activation of complement or PMNs with the subsequent release of reactive oxygen species. The exact pathogenic mechanism, however, remains unknown.⁶

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  HSP is preceded by an upper respiratory tract infection in up to 90 percent of patients (Figure 175-1).⁷ Many different respiratory pathogens have been linked to HSP, including group A β-hemolytic streptococcus.^1,5,7,8

  
  
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  Although many studies have speculated that a potential relationship exists between respiratory pathogens and the development of HSP, no single pathogen has shown to be the definitive causal agent.¹

  
  
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  Risk factors for renal disease in HSP remain unclear. Older age at onset, persistent purpura, and severe abdominal pain have been cited by some studies as risk factors for the development of renal disease.^9–11

  
  
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  Some experts hypothesize a genetic susceptibility towards the development of HSP as well as toward renal involvement; however, no definitive genetic polymorphism has been linked to the disease.^2,6,12

  
  
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  HSP is more common in children with a history of familial Mediterranean fever.^2,13

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  HSP is a clinical diagnosis.⁵

  
  
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  Diagnostic criteria include—The presence of nonthrombocytopenic palpable purpura (considered a mandatory criteria) plus at least one of the following four clinical features:^5,14

  
  
  
  
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    Diffuse abdominal pain.

    
    
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    Any biopsy showing predominantly IgA deposition.

    
    
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    Arthritis or arthralgia.

    
    
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    Renal involvement (proteinuria and/or hematuria).

  
  
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  The majority of children do not require renal or skin biopsy to confirm diagnosis unless severe renal involvement is suspected or skin findings appear atypical.¹⁵

  
  
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  Biopsy of the purpura, as well as of nonaffected areas, will reveal IgA deposition under immunofluorescence.¹⁵

  
  
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  Renal biopsy will demonstrate mesangial proliferation and focal necrosis, classically described as a “focal and segmental proliferative glomerulonephritis.” Cresecent formation is evident in cases of rapidly progressive disease.^2,15

Clinical Features

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  The classic palpable, purpuric rash is essential for diagnosis.² It is the presenting symptom in over half of the cases of HSP; however, it may not always be seen at initial presentation.^2,16,17

  
  
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  Both joint pain and abdominal pain may precede the classic rash in up to 43 percent of patients by up to two weeks.^1,2

  
  
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  The purpura are typically 2 to 10 mm in diameter and accompanied by scattered pinpoint petechiae and ecchymoses (Figure 175-2).¹

  
  
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  The rash may appear urticarial or macular-papular for the first 24 hours.¹

  
  
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  Bullous lesions may develop in some children.¹

  
  
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  Fatigue and low-grade fever are common.¹⁸

  
  
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  Joint pain is present in up to 82 percent of patients. It most often involves the lower extremities, including the feet, ankles, and knees; however, up to 37 percent of patients may have additional pain in the hands, wrists and elbows.^1,2

  
  
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  Abdominal pain is present in 50 percent to 75 percent of cases of HSP (Figure 175-3). It is described as “colicky,” or a “bowel angina,” and may be accompanied by vomiting.^1,2,6

  
  
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  The abdominal pain is often considered mild, however severely debilitating pain may occur in some individuals.²

  
  
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  Gastrointestinal bleeding, either gross or occult, is noted in approximately half of children with abdominal pain related to HSP.¹

  
  
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  Renal involvement is present in approximately 50 percent of cases.^5,19,20

  
  
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  While rarely severe, renal manifestations can range from mild and benign to a rapidly progressive glomerulonephritis with crescent formation and renal failure.^20,21

  
  
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  Nephritis is typically evidenced by microscopic hematuria with or without proteinuria; however, macroscopic hematuria may also be present.^2,21

  
  
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  Some children with renal involvement may also have hypertension.²

  
  
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  A less common clinical feature includes testicular involvement in male children. This may present as epididymitis or orchitis with swelling and pain.^1,2,16 Testicular involvement may be the presenting symptom in some male children.¹⁶

  
  
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  CNS involvement is rare, but may occur. Headache, seizures, intracranial hemorrhage and cerebral vasculitis may be present in about 2 percent of patients.^2,22

  
  
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  Most CNS manifestations are mild and resolve without permanent consequences. Severe or fatal neurologic complications are very rare.²²