View source for Henoch–Schönlein purpura

{{Infobox medical condition (new)
| name            = Henoch–Schönlein purpura
| synonyms        = IgA vasculitis,<ref name="ChapelHill">{{cite journal |author1=J. C. Jennette |author2=R. J. Falk |author3=P. A. Bacon |display-authors=etal |date=January 2013 |title=2012 Revised International Chapel Hill Consensus Conference Nomenclature of Vasculitides |journal=[[Arthritis & Rheumatology|Arthritis & Rheumatism]] |volume=65 |issue=1 |pages=1–11 |doi=10.1002/art.37715 |pmid=23045170|doi-access=free }}</ref> anaphylactoid purpura,<ref name="Bolognia"/> purpura rheumatica,<ref name="Bolognia"/> Schönlein–Henoch purpura<ref name="Bolognia">{{cite book |vauthors=Rapini RP, Bolognia JL, Jorizzo JL |title=Dermatology |publisher=Mosby |location=St. Louis |year=2007 |isbn=978-1-4160-2999-1}}</ref>
| image           = Henoch-schonlein-purpura.jpg
| caption         = Typical purpura on lower legs and [[buttocks]]
| pronounce       = {{IPAc-en|ˈ|h|ɛ|n|ə|k|_|ˈ|ʃ|ɜː|n|l|aɪ|n|,_|ˈ|ʃ|oʊ|n|-}}
| field           = [[Rheumatology]], [[Immunology]]
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'''Henoch–Schönlein purpura''' ('''HSP'''), also known as '''IgA vasculitis''', is a disease of the [[skin]], [[mucous membrane]]s, and sometimes other [[organ (anatomy)|organs]] that most commonly affects [[child]]ren. In the skin, the disease causes [[palpable purpura]] (small, raised areas of bleeding underneath the skin), often with [[arthralgia|joint pain]] and [[abdominal pain]]. With [[kidney]] involvement, there may be a loss of small amounts of [[blood]] and [[protein]] in the [[urine]] ([[hematuria]] and [[proteinuria]]), but this usually goes unnoticed; in a small proportion of cases, the kidney involvement proceeds to [[chronic kidney disease]]. HSP is often preceded by an [[infection]], such as a [[pharyngitis|throat infection]].

HSP is a systemic [[vasculitis]] ([[inflammation]] of [[blood vessel]]s) and is characterized by deposition of [[immune complex]]es containing the antibody [[immunoglobulin A]] (IgA); the exact cause for this phenomenon is unknown. In children, it usually resolves within several weeks and requires no treatment apart from symptom control but may relapse in a third of cases and cause irreversible kidney damage in about one in a hundred cases. In adults, the prognosis is different from in children. The average duration of cutaneous lesions is 27.9 months.<ref name=dermatol1998>{{cite journal |vauthors=Sais G, Vidaller A, Jucglà A, Servitje O, Condom E, Peyri J|title=Prognostic factors in leukocytoclastic vasculitis: a clinicopathologic study of 160 patients |journal=Arch Dermatol |volume=134 |issue=3 |pages=309–15 |year=1998 |pmid=9521029|doi=10.1001/archderm.134.3.309 |doi-access=free }}</ref> For many, it tends to be [[relapsing–remitting]] over a long period of time, rather than self-limiting and there tend to be more complications.<ref name=rheumatologistaug2016>{{cite journal |journal=The Rheumatologist |title=Treatment Challenges, Uncertainty Abound with IgA Vasculitis |year=2016 |url=http://www.the-rheumatologist.org/article/treatment-challenges-uncertainty-abound-iga-vasculitis/?singlepage=1&theme=print-friendly}}</ref>

== Signs and symptoms ==
[[File:purpura.jpg|thumb|Typical [[purpura]] on lower leg]]
[[File:Purpura2.JPG|thumb|More severe case of HSP on child's foot, leg, and arm]]
[[Purpura]], [[arthritis]], and [[abdominal pain]] are known as the "classic triad" of Henoch–Schönlein purpura.<ref name=Kraft1998>{{cite journal |vauthors=Kraft DM, Mckee D, Scott C |title=Henoch–Schönlein purpura: a review |journal=American Family Physician |volume=58 |issue=2 |pages=405–8, 411 |year=1998 |pmid=9713395 |url=http://www.aafp.org/afp/980800ap/kraft.html |access-date=2007-12-15 |archive-date=2011-06-06 |archive-url=https://web.archive.org/web/20110606052544/http://www.aafp.org/afp/980800ap/kraft.html |url-status=dead }}</ref> Purpura occur in all cases, joint pains and arthritis in 80%, and abdominal pain in 62%. Some include [[Gastrointestinal bleeding|gastrointestinal hemorrhage]] as a fourth criterion; this occurs in 33% of cases, sometimes, but not necessarily always, due to [[Intussusception (medical disorder)|intussusception]].<ref name=Saulsbury1999>{{cite journal |author=Saulsbury FT |title=Henoch–Schönlein purpura in children. Report of 100 patients and review of the literature |journal=Medicine (Baltimore) |volume=78 |issue=6 |pages=395–409 |year=1999 |pmid=10575422 |doi=10.1097/00005792-199911000-00005}}</ref> The purpura typically appear on the legs and buttocks, but may also be seen on the arms, face and trunk. The abdominal pain is colicky in character, and may be accompanied by nausea, vomiting, constipation or diarrhea. There may be blood or mucus in the stools.<ref>{{cite book |author=Fauci AS |veditors=Braunwald E, Isselbacher KJ, Petersdorf RG, Wilson JD, Martin JB, Fauci AS |title=Harrison's Book of Internal Medicine |edition=11th|volume=2|year=1987|publisher=McGraw Hill|isbn=978-0-07-079454-2|pages=1441 |chapter=269:The Vasculitis Syndromes}}</ref> The joints involved tend to be the [[ankle]]s, [[knee]]s, and [[elbow]]s, but arthritis in the hands and feet is possible; the arthritis is nonerosive and hence causes no permanent deformity.<ref name=Kraft1998/> Forty percent have evidence of [[kidney]] involvement, mainly in the form of [[hematuria]] (blood in the urine), but only a quarter will have this in sufficient quantities to be noticeable without laboratory tests.<ref name=Saulsbury1999/> Problems in other organs, such as the [[central nervous system]] (brain and spinal cord) and [[lung]]s may occur, but is much less common than in the skin, bowel and kidneys.<ref name=Saulsbury2001>{{cite journal |author=Saulsbury FT |title=Henoch–Schönlein purpura |journal=Current Opinion in Rheumatology |volume=13 |issue=1 |pages=35–40 |year=2001 |pmid=11148713 |doi=10.1097/00002281-200101000-00006}}</ref>

Of the 40% of patients who develop kidney involvement, almost all have evidence (visible or on [[urinalysis]]) of blood in the urine. More than half also have [[proteinuria]] (protein in the urine), which in one eighth is severe enough to cause [[nephrotic syndrome]] (generalised swelling due to low protein content of the blood). While abnormalities on urinalysis may continue for a long time, only 1% of all HSP patients develop [[chronic kidney disease]].<ref name=Saulsbury2001/> [[Hypertension]] (high blood pressure) may occur. Protein loss and high blood pressure, as well as the features on [[biopsy]] of the kidney if performed, may predict progression to advanced kidney disease. Adults are more likely than children to develop advanced kidney disease.<ref name=Saulsbury2001/><ref name=Shrestha2006>{{cite journal  |vauthors=Shrestha S, Sumingan N, Tan J, etal |title=Henoch Schönlein purpura with nephritis in adults: adverse prognostic indicators in a UK population |journal=QJM |volume=99 |issue=4 |pages=253–65 |year=2006 |pmid=16565522 |doi=10.1093/qjmed/hcl034| url=http://qjmed.oxfordjournals.org/cgi/content/full/99/4/253|doi-access=free }}</ref>

== Pathophysiology ==
Henoch–Schönlein purpura is a small-vessel vasculitis in which complexes of [[immunoglobulin A]] (IgA) and [[complement component 3]] (C3) are deposited on arterioles, capillaries, and venules (hence it is a type III hypersensitivity reaction). The activation of the alternative complement pathway results in the deposition of IgA aggregates or IgA complexes in target organs (with deposition of C3)<ref>Song Y, Huang X, Yu G, et al. Pathogenesis of IgA Vasculitis: An Up-To-Date Review. Front Immunol. 2021;12:771619. Published 2021 Nov 9. doi:10.3389/fimmu.2021.771619</ref>. This leads to  the production of inflammatory mediators, including vascular prostaglandins like prostacyclin, which may play a key role in the development of IgAV and its organ-specific clinical manifestations. <ref>Turi S, Belch JJ, Beattie TJ, Forbes CD. Abnormalities of vascular prostaglandins in Henoch-Schönlein purpura. Arch Dis Child. 1986 Feb;61(2):173-7. doi: 10.1136/adc.61.2.173. PMID: 2420289; PMCID: PMC1777583.</ref>As with [[IgA nephropathy]], serum levels of IgA are high in HSP and there are identical findings on renal biopsy; however, IgA nephropathy has a predilection for young adults while HSP is more predominant among children. Further, IgA nephropathy typically only affects the kidneys while HSP is a systemic disease. HSP involves the skin and connective tissues, scrotum, joints, gastrointestinal tract and kidneys.<ref name="Rai1999"/> The genetic basis remains unclear except for involvement of the human leukocyte antigen region of the genome.<ref>{{Cite journal|last1=López-Mejías|first1=Raquel|last2=Castañeda|first2=Santos|last3=Genre|first3=Fernanda|last4=Remuzgo-Martínez|first4=Sara|last5=Carmona|first5=F. David|last6=Llorca|first6=Javier|last7=Blanco|first7=Ricardo|last8=Martín|first8=Javier|last9=González-Gay|first9=Miguel A.|date=March 2018|title=Genetics of immunoglobulin-A vasculitis (Henoch–Schönlein purpura): An updated review|journal=Autoimmunity Reviews|language=en|volume=17|issue=3|pages=301–315|doi=10.1016/j.autrev.2017.11.024|pmid=29353097|doi-access=free}}</ref>
It is hypothesized to involve autoimmunity triggered by infections. Streptococcus strains and Parainfluenza virus are the most commonly associated pathogens, and in children Human Parvovirus B19 is a frequent viral trigger<ref>Hetland LE, Susrud KS, Lindahl KH, Bygum A. Henoch-Schönlein Purpura: A Literature Review. Acta Derm Venereol. 2017 Nov 15;97(10):1160-1166. doi: 10.2340/00015555-2733. PMID: 28654132.</ref>

== Diagnosis ==
[[File:Henoch-Schönlein nephritis IgA immunostaining.jpg|thumb|[[Immunohistochemistry|Immunostaining]] showing IgA in the [[Glomerulus (kidney)|glomerulus]] of a patient with Henoch–Schönlein [[nephritis]]]]
The diagnosis is based on the combination of the symptoms, as very few other diseases cause the same symptoms together. [[Blood test]]s may show elevated [[creatinine]] and [[urea]] levels (in kidney involvement), raised [[IgA]] levels (in about 50%<ref name="Rai1999"/>), and raised [[C-reactive protein]] (CRP) or [[erythrocyte sedimentation rate]] (ESR) results; none are specific for Henoch–Schönlein purpura. The [[platelet]] count may be raised, and distinguishes it from diseases where low platelets are the cause of the purpura, such as [[idiopathic thrombocytopenic purpura]] and [[thrombotic thrombocytopenic purpura]].<ref name=Kraft1998/>

If there is doubt about the cause of the skin lesions, a [[biopsy]] of the skin may be performed to distinguish the purpura from other diseases that cause it, such as [[vasculitis]] due to [[cryoglobulinemia]]; on microscopy, the appearances are of a [[hypersensitivity vasculitis]], and [[immunofluorescence]] demonstrates IgA and [[C3 (complement)|C3]] (a protein of the [[complement system]]) in the blood vessel wall.<ref name=Kraft1998/> However, overall serum complement levels are normal.

On the basis of symptoms, it is possible to distinguish HSP from [[hypersensitivity vasculitis]] (HV). In a series comparing 85 HSP patients with 93 HV patients, five symptoms were found to be indicative of HSP: palpable purpura, [[abdominal angina]], digestive tract hemorrhage (not due to intussussception), hematuria and age less than 20. The presence of three or more of these indicators has an 87% [[Sensitivity (tests)|sensitivity]] for predicting HSP.<ref name="pmid1613701">{{cite journal |vauthors=Michel BA, Hunder GG, Bloch DA, Calabrese LH |title=Hypersensitivity vasculitis and Henoch–Schönlein purpura: a comparison between the 2 disorders |journal=Journal of Rheumatology |volume=19 |issue=5 |pages=721–8 |year=1992 |pmid=1613701}}</ref>

Biopsy of the [[kidney]] may be performed both to establish the diagnosis or to assess the severity of already suspected kidney disease. The main findings on kidney biopsy are increased cells and Ig deposition in the [[mesangium]] (part of the [[glomerulus]], where blood is filtered), [[white blood cell]]s, and the development of [[crescentic glomerulonephritis|crescents]]. The changes are indistinguishable from those observed in [[IgA nephropathy]].<ref name="Rai1999">{{cite journal |vauthors=Rai A, Nast C, Adler S |title=Henoch–Schönlein purpura nephritis |journal=[[Journal of the American Society of Nephrology]] |volume=10 |issue=12 |pages=2637–44 |date=1 December 1999|doi=10.1681/ASN.V10122637 |pmid=10589705 |url=http://jasn.asnjournals.org/cgi/content/full/10/12/2637 |doi-access=free }}</ref>

[[File:HSP IF IgA.jpg|thumb|right|Microphotograph of a [[histology|histological section]] of human skin prepared for direct [[immunofluorescence]] using an anti-IgA antibody, the skin is a biopsy of a patient with Henoch–Schönlein purpura. IgA deposits are found in the walls of small superficial capillaries (yellow arrows). The pale wavy green area on top is the [[Epidermis (skin)|epidermis]], the bottom fibrous area is the [[dermis]].]]

HSP can develop after infections with [[streptococcus|streptococci]] ([[Streptococcus pyogenes|β-haemolytic, Lancefield group A]]), [[hepatitis B]], [[herpes simplex virus]], [[parvovirus B19]], [[Coxsackievirus]], [[adenovirus]], ''[[Helicobacter pylori]]'',<ref name=Saulsbury2001/> [[measles]], [[mumps]], [[rubella]], ''[[Mycoplasma]]'' and numerous others.<ref name=Rai1999/> Drugs linked to HSP, usually as an idiosyncratic reaction, include the antibiotics [[vancomycin]] and [[cefuroxime]], [[ACE inhibitor]]s [[enalapril]] and [[captopril]], anti-inflammatory agent [[diclofenac]], as well as [[ranitidine]] and [[streptokinase]]. Several diseases have been reported to be associated with HSP, often without a causative link. Only in about 35% of cases can HSP be traced to any of these causes.<ref name=Rai1999/>

The exact cause of HSP is unknown, but most of its features are due to the deposition of abnormal antibodies in the wall of blood vessels, leading to [[vasculitis]]. These antibodies are of the subclass IgA<sub>1</sub> in [[polymer]]s; it is uncertain whether the main cause is overproduction (in the digestive tract or the [[bone marrow]]) or decreased removal of abnormal IgA from the circulation.<ref name=Rai1999/> It is suspected that abnormalities in the IgA<sub>1</sub> molecule may provide an explanation for its abnormal behaviour in both HSP and the related condition [[IgA nephropathy]]. One of the characteristics of IgA<sub>1</sub> (and [[IgD]]) is the presence of an 18 [[amino acid]]-long "hinge region" between [[complement system|complement]]-fixating regions 1 and 2. Of the amino acids, half is [[proline]], while the others are mainly [[serine]] and [[threonine]]. The majority of the serines and the threonines have elaborate sugar chains, connected through [[oxygen]] atoms ([[glycosylation#O-linked glycosylation|O-glycosylation]]). This process is thought to stabilise the IgA molecule and make it less prone to [[proteolysis]]. The first sugar is always [[N-acetyl-galactosamine]] (GalNAc), followed by other [[galactose]]s and [[sialic acid]]. In HSP and IgAN, these sugar chains appear to be deficient. The exact reason for these abnormalities is not known.<ref name=Saulsbury2001/><ref name=Rai1999/>

=== Classification ===
Multiple standards exist for defining Henoch–Schönlein purpura, including the 1990 [[American College of Rheumatology]] (ACR) classification<ref name="pmid2202310">{{cite journal  |vauthors=Mills JA, Michel BA, Bloch DA, etal |title=The American College of Rheumatology 1990 criteria for the classification of Henoch–Schönlein purpura |journal=Arthritis and Rheumatism |volume=33 |issue=8 |pages=1114–21 |year=1990 |pmid=2202310 |doi=10.1002/art.1780330809}}</ref><ref name="ACRcriteria">{{cite web |author=American College of Rheumatology |url=http://www.rheumatology.org/practice/clinical/classification/hsp.asp |title=1990 criteria for the classification of Henoch–Schönlein purpura |access-date=2007-12-15 |archive-date=2016-03-03 |archive-url=https://web.archive.org/web/20160303233238/http://www.rheumatology.org/practice/clinical/classification/hsp.asp |url-status=dead }}</ref> and the 1994 Chapel Hill Consensus Conference (CHCC).<ref name="pmid8129773">{{cite journal  |vauthors=Jennette JC, Falk RJ, Andrassy K, etal |title=Nomenclature of systemic vasculitides. Proposal of an international consensus conference |journal=Arthritis and Rheumatism |volume=37 |issue=2 |pages=187–92 |year=1994 |pmid=8129773 |doi=10.1002/art.1780370206|doi-access=free }}</ref> Some have reported the ACR criteria to be more [[Sensitivity (tests)|sensitive]] than those of the CHCC.<ref name="pmid12139664">{{cite journal  |vauthors=Murali NS, George R, John GT, etal |title=Problems of classification of Henoch Schonlein purpura: an Indian perspective |journal=  Clinical and Experimental Dermatology|volume=27 |issue=4 |pages=260–3 |year=2002 |pmid=12139664 |doi=10.1046/j.1365-2230.2002.01063.x|s2cid=45849349 }}</ref>

More recent classifications, the 2006 [[European League Against Rheumatism]] (EULAR) and [[Pediatric Rheumatology Society]] (PReS) classification, include palpable purpura as a mandatory criterion, together with at least one of the following findings: diffuse abdominal pain, predominant IgA deposition (confirmed on skin biopsy), acute arthritis in any joint, and renal involvement (as evidenced by the presence of blood and/or protein in the urine).<ref>{{cite journal  |vauthors=Ozen S, Ruperto N, Dillon MJ, etal |title=EULAR/PReS endorsed consensus criteria* for the classification of childhood vasculitides |journal=Annals of the Rheumatic Diseases |volume=65 |issue=7 |pages=936–41 |date=July 2006 |pmid=16322081 |doi=10.1136/ard.2005.046300 |pmc=1798210}}</ref>

=== Differential diagnosis ===
Henoch–Schönlein purpura may present with an atypical manifestation, which can be confused with [[hives|papular urticaria]], [[systemic lupus erythematosus]], [[meningococcemia]], [[dermatitis herpetiformis]], and  [[acute hemorrhagic edema of infancy]].<ref name=Lawee2008>{{cite journal| author=Lawee D| title=Atypical clinical course of Henoch–Schonlein purpura. | journal=Can Fam Physician | year= 2008 | volume= 54 | issue= 8 | pages= 1117–20 | pmid=18697972 | pmc=2515239 | type= Review. Case Reports. }}</ref>

== Treatment ==
As of 2017, the optimal way to treat Henoch–Schönlein purpura remains controversial.<ref name="Hetland2017">{{cite journal |last1=Hetland |first1=LE |last2=Susrud |first2=KS |last3=Lindahl |first3=KH |last4=Bygum |first4=A |title=Henoch–Schönlein Purpura: A Literature Review |journal=Acta Dermato-venereologica |date=November 2017 |volume=97 |issue=10 |pages=1160–66 |doi=10.2340/00015555-2733 |pmid=28654132|type=Review|doi-access=free }}</ref> [[Analgesic]]s may be needed for the abdominal and joint pains. [[Wound care]] is warranted if the [[Necrosis|skin death]] and ulcerations occur.<ref name="Hetland2017"/> It is uncertain as to whether HSP needs treatment beyond controlling the symptoms. Most people do not receive therapy because of the high spontaneous recovery rate. Experts disagree on whether to routinely use [[corticosteroids]] as treatment for HSP.<ref name="Hetland2017"/> However, if they are given early in the disease episode, the duration of symptoms may be shortened, and abdominal pain can improve significantly.<ref name="Hetland2017"/> Moreover, the chance of severe kidney problems may be reduced.<ref name="pmid17974746">{{cite journal |vauthors=Weiss PF, Feinstein JA, Luan X, Burnham JM, Feudtner C |title=Effects of corticosteroid on Henoch–Schönlein purpura: a systematic review |journal=Pediatrics |volume=120 |issue=5 |pages=1079–87 |year=2007 |pmid=17974746 |doi=10.1542/peds.2007-0667 |pmc=3525094}}</ref> A systematic review did not find any evidence that steroid treatment ([[prednisone]]) is effective at decreasing the likelihood of developing long-term kidney disease.<ref name=Hahn2015>{{Cite journal|last1=Hahn|first1=Deirdre|last2=Hodson|first2=Elisabeth M.|last3=Willis|first3=Narelle S.|last4=Craig|first4=Jonathan C.|date=2015-08-07|title=Interventions for preventing and treating kidney disease in Henoch–Schönlein purpura (HSP)|journal=The Cochrane Database of Systematic Reviews|issue=8|pages=CD005128|doi=10.1002/14651858.CD005128.pub3|issn=1469-493X|pmid=26258874}}</ref>

Evidence of worsening kidney damage would normally prompt a kidney biopsy. Treatment may be indicated on the basis of the appearance of the biopsy sample; various treatments may be used, ranging from steroids by mouth to a combination of intravenous [[methylprednisolone]] (steroid), [[cyclophosphamide]] and [[dipyridamole]] followed by prednisone. Other regimens include steroids/[[azathioprine]], and steroids/cyclophosphamide (with or without [[heparin]] and [[warfarin]]). [[Intravenous immunoglobulin]] (IVIG) is occasionally used.<ref name=Rai1999/>

There is no good evidence that treating children who have HSP with [[Antiplatelet drug|antiplatelet]] agent prevents persistent kidney disease.<ref name=Hahn2015 /> There is also no evidence that treating children or adults with cyclophosphamide prevents severe kidney disease.<ref name=Hahn2015 /> Heparin treatment is not justified.<ref name=Hahn2015 />

== Prognosis ==
Overall prognosis is good in most patients, with one study showing recovery occurring in 94% and 89% of children and adults, respectively (some having needed treatment).<ref name="pmid9153547">{{cite journal |vauthors=Blanco R, Martínez-Taboada VM, Rodríguez-Valverde V, García-Fuentes M, González-Gay MA |title=Henoch–Schönlein purpura in adulthood and childhood: two different expressions of the same syndrome |journal=Arthritis and Rheumatism |volume=40 |issue=5 |pages=859–64 |year=1997 |pmid=9153547 |doi=10.1002/art.1780400513|doi-access=free }}</ref> In children under ten, the condition recurs in about a third of all cases, usually within the four months of the initial attack.<ref name="Saulsbury1999"/> Recurrence is more common in older children and adults.<ref name=Saulsbury2001/>

=== Kidney involvement ===
In adults, kidney involvement progresses to [[end-stage kidney disease]] (ESKD) more often than in children. In a UK series of 37 patients, 10 (27%) developed advanced kidney disease. Proteinuria, hypertension at presentation, and pathology features (crescentic changes, interstitial fibrosis and tubular atrophy) predicted progression.<ref name=Shrestha2006/> About 20% of children that exhibit nephrotic or nephritic features experience long permanent renal impairment.<ref name=5yearReview>{{cite journal|last=Watson|first=L|author2=Richardson, AR |author3=Holt, RC |author4=Jones, CA |author5= Beresford, MW |title=Henoch schonlein purpura--a 5-year review and proposed pathway.|journal=PLOS ONE|date=January 2012|volume=7|issue=1|pages=e29512|pmid=22235302|doi=10.1371/journal.pone.0029512|pmc=3250434|bibcode=2012PLoSO...729512W|doi-access=free}}</ref>

The findings on [[renal biopsy]] correlate with the severity of symptoms: those with asymptomatic hematuria may only have focal mesangial proliferation while those with proteinuria may have marked cellular proliferation or even crescent formation. The number of crescentic glomeruli is an important prognostic factor in determining whether the patient will develop chronic renal disease.<ref name=Saulsbury2001/>

In ESKD, some eventually need [[hemodialysis]] or equivalent renal replacement therapy (RRT). If a [[kidney transplant]] is found for a patient on RRT, the disease will recur in the graft (transplanted kidney) in about 35% of cases, and in 11%, the graft will fail completely (requiring resumption of the RRT and a further transplant).<ref name=Rai1999/>

== Epidemiology ==
HSP occurs more often in children than in adults,<ref name="pmid9153547" /> and usually follows an [[upper respiratory tract infection]]. [[Median|Half of affected patients]] are below the age of six, and 90% are under ten. It occurs about twice as often in boys as in girls.<ref name=Saulsbury2001/> The [[incidence (epidemiology)|incidence]] of HSP in children is about 20 per 100,000 children per year, making it the most common vasculitis in children.<ref name=Gardner-Medwin2002>{{cite journal |vauthors=Gardner-Medwin JM, Dolezalova P, Cummins C, Southwood TR |title=Incidence of Henoch–Schönlein purpura, Kawasaki disease, and rare vasculitides in children of different ethnic origins |journal=Lancet |volume=360 |issue=9341 |pages=1197–202 |year=2002 |pmid=12401245 |doi=10.1016/S0140-6736(02)11279-7|s2cid=25018798 }}</ref>

Cases of HSP may occur anytime throughout the year, but some studies have found that fewer cases occur during the summer months.<ref>{{cite journal|author=Saulsbury FT|title=Epidemiology of Henoch–Schönlein purpura|journal=Cleveland Clinic Journal of Medicine|year=2002|volume=69 Suppl 2|pages=SII87–9|pmid=12086273|url=http://www.ccjm.org/content/69/Suppl_2/SII87.full.pdf+html|doi=10.3949/ccjm.69.suppl_2.sii87|access-date=2012-08-26|archive-date=2020-03-27|archive-url=https://web.archive.org/web/20200327165812/http://www.ccjm.org/content/69/Suppl_2/SII87.full.pdf+html|url-status=dead}}</ref>

== History ==
The disease is [[eponym|named after]] [[Eduard Heinrich Henoch]] (1820–1910), a German [[pediatrics|pediatrician]] (nephew of [[Moritz Heinrich Romberg]]) and his teacher [[Johann Lukas Schönlein]] (1793–1864), who described it in the 1860s. Schönlein associated the purpura and arthritis, and Henoch the purpura and gastrointestinal involvement. The English [[internal medicine|physician]] [[William Heberden]] (1710–1801) and the [[dermatology|dermatologist]] [[Robert Willan]] (1757–1812) had already described the disease in 1802 and 1808, respectively, but the name ''Heberden–Willan disease'' has fallen into disuse. [[William Osler]] was the first to recognise the underlying [[allergy|allergic]] mechanism of HSP.<ref>{{WhoNamedIt|synd|1022|Schönlein-Henoch purpura}}</ref>

== See also ==
* [[Cutaneous small-vessel vasculitis]]

== References ==
{{Reflist}}

== External links ==
{{Medical resources
|  DiseasesDB     = 5705  
|  ICD10          = {{ICD10|D|69|0|d|65}}<br />([[ILDS]] D69.010) 
|  ICD9           = {{ICD9|287.0}} 
|  ICDO           =  
|  OMIM           =  
|  MedlinePlus    = 000425 
|  eMedicineSubj  = derm 
|  eMedicineTopic = 177  
|  eMedicine_mult = {{eMedicine2|emerg|767}} {{eMedicine2|emerg|845}} {{eMedicine2|ped|3020}} 
|  MeshID         = D011695
}}
{{commons category}}

{{Hypersensitivity and autoimmune diseases}}
{{Systemic vasculitis}}

{{good article}}

{{DEFAULTSORT:Henoch-Schonlein Purpura}}
[[Category:Rheumatology]]
[[Category:Pediatrics]]
[[Category:Nephrology]]
[[Category:Autoimmune diseases]]
[[Category:Ailments of unknown cause]]
[[Category:Vascular-related cutaneous conditions]]