Henoch Schonlein Purpura (HSP)

01Pathophysiology

Henoch-Schonlein Purpura (HSP), now formally termed IgA vasculitis, is the most common systemic vasculitis in children. It is classified as a small vessel vasculitis characterized by the deposition of IgA-dominant immune complexes in the walls of arterioles, capilloles, and postcapillary venules.

The disease is most often triggered by a preceding infection, with Group A Streptococcus being the most frequently identified pathogen. Other triggers include Mycoplasma, adenovirus, parvovirus B19, certain medications (e.g., vancomycin, ACE inhibitors), and vaccinations. In response to these antigens, the immune system generates an abnormal IgA1 antibody response. These IgA1 molecules are galactose-deficient, making them prone to forming self-aggregating immune complexes. The complexes circulate and deposit in the walls of small vessels, activating the alternative complement pathway and triggering an inflammatory cascade with neutrophilic infiltration.

This vascular inflammation produces the four hallmark organ manifestations. In the skin, small dermal vessel inflammation leads to extravasation of red blood cells, producing the classic palpable purpura. In the gastrointestinal tract, submucosal vessel involvement causes edema, hemorrhage, and sometimes intussusception. In the joints, synovial vessel inflammation produces periarticular swelling and pain. In the kidneys, IgA deposits in the glomerular mesangium cause a proliferative glomerulonephritis that is histologically indistinguishable from IgA nephropathy (Berger disease). The key conceptual link to remember is that HSP nephritis and IgA nephropathy are considered the same disease on a spectrum: HSP is the systemic form and Berger disease is the renal-limited form.

02Classification and Clinical Manifestation

The EULAR/PRINTO/PRES classification criteria require palpable purpura (mandatory criterion) plus at least one of the following:

An important clinical sequencing point: the purpura does not always appear first. In roughly one-third of cases, abdominal pain or joint symptoms precede the rash by days, making early diagnosis challenging and leading to unnecessary surgical evaluations.

03Diagnostic Workup

Best initial test: HSP is fundamentally a clinical diagnosis. When a child between 3 and 10 years old presents with palpable purpura on the lower extremities and buttocks alongside joint pain and abdominal symptoms after a recent URI, the diagnosis is made at the bedside. The single most important initial laboratory step is a CBC with platelet count to confirm that platelets are normal. This immediately separates HSP from thrombocytopenic causes of purpura such as immune thrombocytopenic purpura (ITP), thrombotic thrombocytopenic purpura (TTP), or disseminated intravascular coagulation (DIC). A urinalysis must be obtained to screen for renal involvement, as nephritis is the primary determinant of long-term morbidity.

Most accurate (confirmatory) test: When the presentation is atypical or the diagnosis is uncertain, a skin biopsy with direct immunofluorescence is the gold standard. The hallmark finding is leukocytoclastic vasculitis with perivascular IgA deposition. If renal involvement is significant (persistent proteinuria exceeding 1 g/day, nephrotic syndrome, or declining renal function), a renal biopsy is indicated. The histologic pattern mirrors IgA nephropathy, showing mesangial proliferation and IgA deposits on immunofluorescence.

All patients require serial urinalyses for at least 6 months after diagnosis, because nephritis can develop weeks after the initial presentation.

04Management and Treatment

Acute stabilization: For most children, HSP is a self-limited condition requiring only supportive care. NSAIDs are the first-line treatment for arthralgia. The role of corticosteroids remains important primarily for severe abdominal pain and GI complications, where early steroid use can reduce symptom duration and may decrease the risk of intussusception or perforation. It is important to note that corticosteroids have not been definitively proven to prevent nephritis, although they may reduce the severity of early renal involvement in some studies.

Long-term management: The kidneys are the organ that determines the ultimate prognosis. Mild hematuria and low-grade proteinuria typically resolve spontaneously. When proteinuria is persistent and exceeds 1 g/day, an ACE inhibitor should be started to reduce intraglomerular pressure and limit proteinuria progression. Patients with biopsy-proven crescentic glomerulonephritis or rapidly progressive renal failure require aggressive immunosuppression.

Follow-up protocol: All patients, even those with no initial renal findings, must have urinalysis and blood pressure monitoring at weekly intervals for the first month, then monthly for 6 months. Renal involvement can appear as late as 6 months after initial presentation.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common trap with HSP is confusing it with ITP because both present with purpura in a child following a viral illness. The discriminator is the platelet count: if the vignette tells you the platelets are normal, think HSP; if the platelets are low, think ITP. A second frequent mistake is anchoring on the purpura as the first symptom. Test-writers love to present an atypical sequence where the child comes in with severe colicky abdominal pain or joint swelling before the rash appears, leading students to pursue surgical diagnoses or juvenile idiopathic arthritis. The appearance of palpable purpura on the buttocks and lower extremities a few days later clinches the diagnosis.

Another commonly tested point is the distinction between the intussusception seen in HSP and the classic pediatric intussusception. Standard pediatric intussusception is ileocecal and responds well to air or barium enema reduction. HSP-associated intussusception is ileoileal, which is less amenable to enema reduction and more likely to require surgery.

The most testable long-term concept is renal monitoring. Questions will often present a child who recovered from HSP weeks ago and now shows up with cola-colored urine or peripheral edema. The core competency being assessed is recognizing that nephritis can be a delayed complication appearing weeks to months after initial resolution, and that serial urinalysis for at least 6 months is the standard of care. When a question stem asks for the "next best step" in a child with resolved HSP and new-onset proteinuria, the answer is to quantify the proteinuria and consider renal biopsy if it is significant, not to simply reassure the family that the disease is over.