Vasculitis from the pediatric perspective

Vasculitis: do we know more to classify better?

The systemic vasculitides are a heterogeneous group of disorders characterized by the inflammation of blood vessels. The development and implementation of advanced diagnostic tests and genetic studies have resulted in substantial improvement in our understanding of vasculitis pathogenesis, resulting in the revision of the nomenclature and classification for vasculitis. Multicenter, collaborative studies are currently underway to develop improved diagnostic criteria. In this review, the major nomenclature and classification systems for vasculitides are summarized, with special emphasis on those emerging from the recent 2012 Chapel Hill Consensus Conference (CHCC).

The Molecular Biology and Treatment of Systemic Vasculitis in Children

Primary systemic vasculitides are rare in childhood but are associated with significant morbidity and mortality. The cause of the majority of vasculitides is unknown, although it is likely that a complex interaction between environmental factors, such as infections and inherited host responses, triggers the disease and determines the vasculitis phenotype. Several genetic polymorphisms in vasculitides have now been described, which may be relevant in terms of disease predisposition or development of disease complications. Treatment regimens continue to improve with the use of different immunosuppressive medications and newer therapeutic approaches such as biologic agents. This chapter reviews recent studies shedding light on the pathogenesis of vasculitis with emphasis on molecular biology where known, and summarizes current treatment strategies. We discuss new emerging challenges particularly with respect to the long-term cardiovascular morbidity for children with systemic vasculitis and emphasize the importance of future international multicenter collaborative studies to further increase and standardize the scientific base investigating and treating childhood vasculitis.

Time to focus on outcome assessment tools for childhood vasculitis

Childhood systemic vasculitides are a group of rare diseases with multi-organ involvement and potentially devastating consequences. After establishment of new classification criteria (Ankara consensus conference in 2008), it is now time to establish measures for proper definition of activity and damage in childhood primary vasculitis. By comparison to adult vasculitis, there is no consensus for indices of activity and damage assessment in childhood vasculitis. Assessment of disease activity is likely to become a major area of interest in pediatric rheumatology in the near future. After defining the classification criteria for primary systemic childhood vasculitis, the next step was to perform a validation study using the original Birmingham vasculitis activity score as well as the disease extent index to measure disease activity in childhood vasculitis. Presently, there are efforts in place to develop a pediatric vasculitis activity score. This paper reviews the current understanding about the assessment tools (i.e., clinical features, laboratory tests, radiologic assessments, etc.) widely used for evaluation of the disease activity and damage status of the children with vasculitis.

Henoch-Schönlein purpura in a child with Guillain-Barré syndrome

A case of Henoch-Schönlein purpura with Guillain-Barré syndrome in a 3-year-old-girl is presented. This association is extremely rare. During the course of Guillain-Barré syndrome, a decrease in plasma factor XIII activity was noted. When the Guillain-Barré symptoms improved, the factor XIII activity returned to normal. In the present case of Henoch-Schönlein purpura complicated by Guillain-Barré syndrome, the factor XIII level was measured, a novel feature of this study. The findings suggest the involvement of factor XIII, which is characteristically involved in Henoch-Schönlein purpura, also is involved in the associated Guillain-Barré syndrome.

Medium-size-vessel vasculitis

Medium-size-artery vasculitides do occur in childhood and manifest, in the main, as polyarteritis nodosa (PAN), cutaneous PAN and Kawasaki disease. Of these, PAN is the most serious, with high morbidity and not inconsequential mortality rates. New classification criteria for PAN have been validated that will have value in epidemiological studies and clinical trials. Renal involvement is common and recent therapeutic advances may result in improved treatment options. Cutaneous PAN is a milder disease characterised by periodic exacerbations and often associated with streptococcal infection. There is controversy as to whether this is a separate entity or part of the systemic PAN spectrum. Kawasaki disease is an acute self-limiting systemic vasculitis, the second commonest vasculitis in childhood and the commonest cause of childhood-acquired heart disease. Renal manifestations occur and include tubulointerstitial nephritis and renal failure. An infectious trigger and a genetic predisposition seem likely. Intravenous immunoglobulin (IV-Ig) and aspirin are effective therapeutically, but in resistant cases, either steroid or infliximab have a role. Greater understanding of the pathogenetic mechanisms involved in these three types of vasculitis and better long-term follow-up data will lead to improved therapy and prediction of prognosis.

Henoch-schönlein purpura complicated by reversible posterior leukoencephalopathy syndrome

We report a 7-year-old girl with Henoch-Schönlein purpura who developed hypertensive encephalopathy. She showed a sudden onset of neurological symptoms, including hypertension, convulsions, disturbance of consciousness, and cortical blindness. Reversible posterior leukoencephalopathy syndrome was diagnosed from the findings on magnetic resonance imaging. Reports of this syndrome in patients with Henoch-Schönlein purpura are very rare. However, if symptoms suggest central nervous system involvement, neuroimaging should be done for rapid diagnosis, and immediate treatment should be provided to avoid sequelae.

Vasculitis in children

Primary systemic vasculitides of the young are relatively rare diseases, but can have a significant morbidity and mortality. The purpose of this review is to provide an overview of the paediatric vasculitides. Vasculitides that predominantly affect children will be considered in more detail than vasculitic diseases that although are seen in children affect adults more commonly, such as the ANCA associated vasculitides. New classification criteria for childhood vasculitis have recently been proposed and are currently undergoing validation. Epidemiological clues continue to implicate infectious triggers in Kawasaki Disease and Henoch Schönlein purpura. Several genetic polymorphisms have now been described in the vasculitides that may be relevant in terms of disease predisposition or development of disease complications. Treatment regimens continue to improve, with the use of different immunosuppressive medications and newer therapeutic approaches such as biologic agents. However new challenges are looming in regards to the role of inflammation in endothelial health and the long term cardiovascular morbidity for children with primary systemic vasculitis. International multicenter collaboration is of utmost importance in order for us to further advance our understanding and improve the treatment and outcome of systemic vasculitis in the young.

Biologic therapy in primary systemic vasculitis of the young

OBJECTIVES

To describe the biologic treatment regimens and report the efficacy and safety of biologic therapies in a multicentre series of children with primary systemic vasculitis (PSV).

METHODS

This was a retrospective descriptive case series of children with PSV treated with biologic therapy between February 2002 and November 2007. Primary retrospective outcome assessment measures were: daily corticosteroid dose; Birmingham Vasculitis Activity Score (BVAS); and adverse events (including infection rate).

RESULTS

Twenty-five patients median age 8.8 (range 2.4-16) years; 11 male with active PSV (n = 6 with anti-neutrophil cytoplasmic antibody associated vasculitides, n = 11 with polyarteritis nodosa, n = 7 with unclassified vasculitis and n = 1 with Behçet's disease) were treated with biologic agents including infliximab (n = 7), rituximab (n = 6), etanercept (n = 4), adalimumab (n = 1) or multiple biologics sequentially (n = 7). Overall, there was a significant reduction in BVAS from a median of 8.5 (range 5-32) at start of therapy to 4 (range 0-19) at median 32 months follow-up (P = 0.003) accompanied by significant reduction in median daily prednisolone requirement from 1 (range 0.2-2) to 0.25 (range 0-1) mg/kg/day, P = 0.000. For those receiving multiple biologic agents sequentially, a similar clinical improvement was observed with corticosteroid sparing. Infections occurred in 24%, the most severe in those receiving infliximab.

CONCLUSION

Our data provide retrospective evidence of efficacy of these agents, and highlight the associated infectious complications. Further multicentre standardization of treatment protocols and data collection to inform clinical trials of biologic therapy in systemic vasculitis of the young is required.

Vasculitis in children

Vasculitis is rare in children, and, apart from HSP and perhaps KD, most practicing pediatricians will never encounter a case. Nonetheless, progress in the diagnosis and treatment of these conditions has afforded most children with vasculitis a reasonably good prognosis. Accordingly, it is important to consider vasculitis as a potential cause of unexplained inflammation, perplexing rashes, or strange combinations of symptoms. Although evaluation and management of suspected vasculitis are difficult in the best of situations, they are impossible if the diagnosis is not considered.

Henoch–Schönlein purpura nephritis complicated by reversible posterior leukoencephalopathy syndrome

We report a young female patient with Henoch-Schönlein purpura (HSP) nephritis complicated by reversible posterior leukoencephalopathy syndrome (RPLS). The patient suddenly showed generalized seizures and cortical blindness with severe hypertension due to renal insufficiency approximately 1 year after cessation of corticosteroid treatment for HSP nephritis. Magnetic resonance imaging (MRI) demonstrated bilateral abnormal signals mainly in the cerebellum and white matter of the occipital lobe. Clinical symptoms quickly improved in conjunction with disappearance of abnormal signals on brain MRI after starting control of hypertension and continuous hemodiafiltration with steroid pulse therapy and plasmapheresis. RPLS may be caused by vasculitis and also by hemodynamic change due to severe hypertension in HSP, particularly in patients with nephropathy. In such cases intensive treatment should be performed as soon as possible to avoid neurological sequelae.

What's new in the aetiopathogenesis of vasculitis?

The cause of the majority of childhood vasculitides is unknown although it is likely that a complex interaction between environmental factors and inherited host responses trigger the disease and determine the vasculitis phenotype. Epidemiological clues continue to implicate infectious triggers in Kawasaki syndrome (KS) and Henoch Schonlein purpura (HSP). Several genetic polymorphisms have now been described in KS and HSP which predispose to disease or predict disease severity. Anti-neutrophil cytoplasmic antibodies (ANCA) are now known to be directly involved in the pathogenesis of vascular injury in ANCA-associated vasculitides, although why some individuals develop ANCA in the first instance is not yet understood. Endothelial injury and repair are active areas of research in vasculitis. It is now possible to track endothelial injury non-invasively in children with vasculitis using surrogate markers of endothelial injury. The vasculogenic pathways involved in vascular repair following vasculitis, including endothelial progenitor cells, are beginning to be studied. It is anticipated that an improved understanding of the aetiopathogenesis of vasculitis in the young will ultimately shape future novel diagnostic and therapeutic approaches and will help us predict which children may develop premature arteriosclerosis in later life.

Long-term outcome after surgical intervention and interventional procedures for the management of Takayasu’s arteritis in children

OBJECTIVE

There is little information available on the results of reconstructive arterial surgery for Takayasu's arteritis in children. This study evaluates midterm to long-term outcome after surgical, as well as interventional, procedures.

METHODS

From 1984 through 2004, 10 children (5 boys and 5 girls; age, 12.7 +/- 2.6 years) with Takayasu's arteritis were referred to our center. Baseline cardiovascular assessment included contrast angiography (n = 4), magnetic resonance imaging-angiography (n = 3), and combined contrast angiography plus magnetic resonance imaging-angiography (n = 3). Two patients had disease confined to the thoracic aorta, 4 had disease confined to the abdominal aorta, and 4 had combined thoracoabdominal aortic disease. Steno-occlusive lesions were predominant in 92% of cases. Seven patients were maintained on steroid therapy throughout the follow-up period. Eight children underwent complex surgical procedures, 1 patient had balloon dilatation of the renal and mesenteric arteries, and 1 patient had combined vascular surgery with percutaneous transluminal angioplasty. Overall, 24 grafts (polytetrafluoroethylene, Dacron grafts, and cryopreserved homografts) were implanted in various locations.

RESULTS

There were no perioperative deaths. Arterial hypertension regressed in all patients, and cardiac function normalized in all 4 patients with dilative cardiomyopathy. Over a 20-year period, 1 patient presented with sudden death and 2 showed nonfatal disease progression, one of whom required surgical reintervention. The occlusion rate was higher in Dacron grafts.

CONCLUSIONS

Our study shows that despite the extent and severity of vascular lesions, children with Takayasu's arteritis could benefit from reconstructive surgery, with low mortality, morbidity, and satisfactory long-term results.

Vasculitis treatment - new therapeutic approaches

In childhood, vasculitis carries with it a not inconsequential morbidity and mortality. Current therapy is usually effective in inducing remission, but there is a penalty in terms of significant and serious side effects as well as concerns about long-term maintenance regimens. Additionally, some patients are recalcitrant to treatment and options have, hitherto, been limited in relation to alternative therapy. In view of this, novel therapeutic approaches are being explored that include the better use of long-established agents as well as the utilization of newer immunosuppressive and immunomodulatory strategies. Blockade of circulating mediators and surface receptors as well as lymphocyte depletion and immunoablation are being introduced predominantly in adults but increasingly also in children. With greater understanding of the pathogenetic mechanisms involved in the disease processes it is becoming possible to utilize much more focussed therapy for these serious and life-threatening disorders with, hopefully, a decrease in long-term morbidity and mortality as well as a diminution of drug-induced adverse effects.

Systemic vasculitis: a cause of indeterminate intestinal inflammation

OBJECTIVES

Indeterminate intestinal inflammation may result from a variety of inflammatory conditions in addition to ulcerative colitis and Crohn disease. The primary systemic vasculitides may present with intestinal inflammation and an indeterminate colitis. We set out to describe a series of children with primary systemic vasculitis who initially presented with clinical features suggestive of inflammatory bowel disease (IBD) to establish criteria that might help discriminate between IBD and primary systemic vasculitis.

METHODS

Ten children (6 boys, median age at presentation 8.9 years, range 0.9-14.5 years) satisfied inclusion criteria.

RESULTS

All had abdominal pain, weight loss, diarrhea (6 of 10 bloody) and laboratory evidence of a severe acute phase response. Extraintestinal clinical features included vasculitic rash, renal impairment, myalgia, testicular pain and polyarthritis. Endoscopy showed vascular changes or other macroscopic findings suggestive of vasculitis in 5 of 10 patients. Gut histology revealed indeterminate chronic inflammatory mucosal changes and one patient with small artery fibrinoid necrosis in the submucosal vessels. Extraintestinal biopsy was performed in 6 patients and had a higher yield for the demonstration of vasculitis than intestinal biopsy. The results of selective visceral angiography was suggestive of vasculitis in all patients, but was normal in 7 cases of treatment-unresponsive classic IBD. Treatment comprised corticosteroid and azathioprine in all patients. Cyclophosphamide was given to 7 of 10 patients.

CONCLUSIONS

Extraintestinal manifestations and inflammatory responses that may be disproportionate to the degree of intestinal inflammation provide clues to the presence of an underlying primary systemic vasculitis, and these data suggest that selective visceral angiography plays a key role in the diagnosis of vasculitis in this context. It is important to identify and treat any vasculitic component because failure to do so may result in consequential morbidity or mortality.

T-cell receptor repertoire of circulating gamma delta T-cells in Takayasu's arteritis

We studied T-cell receptor (TCR) repertoire of circulating gamma delta (gammadelta) T-cells in 20 patients with Takayasu's arteritis (TA), 20 healthy controls (HC), 7 follow up TA patients, and 10 patients with rheumatoid arthritis (RA) and 5 Wegener's granulomatosis (WG) patients as disease controls. Patients with TA (8.1 +/- 5.1%) compared to HC (3.7 +/- 2.1%, P = 0.014), RA (4.8 +/- 0.6%, P = 0.032), and WG (4.2 +/- 0.8%, P = 0.030) as well as active TA compared to inactive TA (13.9 +/- 4.1% vs. 4.9 +/- 1.5%; P < 0.001) had higher number of gammadelta T-cells. The numbers of Vdelta1+ cells were significantly higher in patients with TA (40.0 +/- 20.8%) than HC (13.1 +/- 8.0%; P = 0.001), RA (19.5 +/- 1.8%, P = 0.004), and WG (17.0 +/- 3.9%, P = 0.007). The numbers of gammadelta T-cells normalized in all the 7 patients after 180 days of follow up (13.9 +/- 4.1% vs. 6.9 +/- 2.5%; P = 0.001). We also observed higher number of activated and IFN-gamma producing gammadelta T-cells in active TA. Our data show that gammadelta T-cells particularly those bearing Vdelta1 TCR may have an important role in the immunopathogenesis of TA.

Vasculitis in children

This article provides a general overview of vasculitis, situations in which the diagnosis should be considered, diagnostic methods, and therapeutic considerations. Details and treatments unique to specific vasculitides are also reviewed.

Cellular and humoral immune responses to mycobacterial heat shock protein-65 and its human homologue in Takayasu's arteritis

Expression of heat shock protein (HSP)-65 as well as infiltration of T-cells in arterial lesions and raised levels of circulating antibodies against mycobacterial HSP65 (mHSP65) led us to the concept that mHSP65 or its human homologue (hHSP60) might be involved in the etiopathogenesis of Takayasu's arteritis (TA). Therefore, we investigated mHSP65 and hHSP60 reactive peripheral blood T-cell subsets by BrdU incorporation assay and flow cytometry as well as investigating the different isotypes of anti-mHSP65 and hHSP60 antibodies by ELISA. Eighty-four percent (22/26) of the TA patients were observed to show T-cell proliferation to mHSP65 and hHSP60 whereas only 16% (3/18) healthy controls showed such proliferation (P <0.001). Both HSPs induced proliferation of exclusively CD4+ T-cells and not CD8+ T-cells. We also observed a significantly higher prevalence of only the IgG isotype reactive to mHSP65 and hHSP60 in TA as compared to HC (mHSP65: 92% TA versus 11% HC, P <0.0001 and hHSP60: 84% versus 22%, P <0.001). Our data show a significant correlation between mHSP65 and hHSP60 reactive T-cells (CD3+: r=0.901; CD4+: r=0.968) as well as anti-mHSP65 and anti-hHSP60 IgG antibodies (r=0.814) suggesting an infection induced autoimmunity in TA, possibly induced by molecular mimicry between mHSP65 and hHSP60 or other tissue specific antigens.

Henoch Schönlein nephritis: clinical findings related to renal function and morphology

We evaluated the renal hemodynamics and the urine protein excretion rates of 73 children with Henoch-Schonlein nephritis (HSN). In 40 children we also performed a renal biopsy. The glomerular filtration rate (GFR) and effective renal plasma flow were determined by the clearances of inulin and para-aminohippurate during water diuresis. Urine albumin and IgG excretion were assessed in short-term timed samples. The mean GFR at the first examination was reduced in the HSN patients and most reduced in those with nephrotic proteinuria. There was an inverse correlation between the GFR at the first examination and the amount of albuminuria and urinary IgG excretion. Among the 40 patients with some degree of proteinuria who underwent a renal biopsy, 9 of 13 patients with mild to moderate proteinuria had severe morphological changes. GFR correlated inversely and fractional albumin and IgG excretion directly with the severity of the pathological findings on the biopsy, and with segmental and global sclerosis, the grade of mesangial proliferation, and interstitial inflammation. In conclusion, GFR is moderately reduced early in HSN and more reduced in patients with more proteinuria and in those with more advanced morphological changes. Moreover, even mild to moderate proteinuria may indicate severe morphological changes, which increase the indications for early renal biopsy in these patients.

Endothelial microparticles and the diagnosis of the vasculitides

Recently there has been considerable interest in a novel surrogate marker of endothelial injury, endothelial microparticles (EMP), in a number of diseases characterised by endothelial injury. This review examines the data relating to EMP in human disease states, and examines the potential for EMP to provide a window onto the activated endothelium in primary systemic vasculitides. The utility of EMP for the diagnosis and monitoring of active vasculitis is discussed.

Aortoarteritis and sensorineural hearing loss in an adolescent black male

We describe an adolescent male having sudden onset of sensorineural hearing loss. Evaluation led to the discovery of marked aortoarteritis. This patient exhibited findings of both Takayasu arteritis and Cogan syndrome. This report emphasizes the importance of ensuring a thorough systemic evaluation in individuals having sudden hearing loss.

Endothelial and platelet microparticles in vasculitis of the young

OBJECTIVE

Microparticles are released from endothelial cells in response to a variety of injurious stimuli and recently have been shown to be increased in a number of diseases associated with endothelial dysfunction. This study examined endothelial microparticle (EMP) and platelet microparticle (PMP) profiles in children with systemic vasculitis to test the hypothesis that EMPs may provide a noninvasive means of examining endothelial activation or injury.

METHODS

The study cohort comprised 39 children with systemic vasculitis at various stages of disease activity, 24 control children with febrile disease, and a control group of 43 healthy subjects. Plasma was ultracentrifuged at 17,000g for 60 minutes, and the microparticle pellets were examined using flow cytometry.

RESULTS

Plasma from patients with active systemic vasculitis contained significantly higher numbers of E-selectin-positive EMPs compared with that from patients in remission, healthy controls, or febrile disease controls (P = 0.000 for each). A similar result was obtained for the numbers of EMPs expressing the marker CD105. There was also a significant increase in PMPs expressing CD42a in the active vasculitis group as compared with the other groups, but this difference was not significant for PMPs expressing P-selectin. The EMP counts correlated with the Birmingham Vasculitis Activity Score and the acute-phase reactant levels in the patients with systemic vasculitis, but there was a poor correlation overall between EMP counts and the acute-phase reactant levels in the febrile disease controls.

CONCLUSION

EMPs may provide a window to the activated endothelium and could provide important pathophysiologic insights into the vascular injury associated with vasculitis of the young.

Anti-annexin V antibodies in Takayasu's arteritis: prevalence and relationship with disease activity

Annexin V has an important role in the regulation of apoptosis and antibodies directed against it have been shown to lead to apoptosis of vascular endothelial cells. To evaluate the role of anti-annexin V antibodies (AA5A) in Takayasu's arteritis (TA), we investigated these antibodies in the sera of 66 TA patients, 50 healthy controls and in the follow-up sera of 12 active TA patients by enzyme-linked immunosorbent assay. The AA5A-positive patients were analysed further for the presence of anti-endothelial cell antibodies (AECA) and anticardiolipin antibodies (ACLA) to determine the relationship of AA5A with these autoantibodies. AA5A were observed in 36% (24/66) of the patients versus 6% (3/50) of the controls (P<0.001) and in 53% (19/36) of patients with active TA versus 17% (5/30) of those with inactive disease (P<0.01). Levels of AA5A were also observed to be significantly higher in patients with TA compared to controls (0.557 +/- 0.362 versus 0.259 +/- 0.069; P<0.0001) and in patients with active disease compared to those with inactive disease (0.700 +/- 0.403 versus 0.385 +/- 0.205; P<0.0001). In the follow-up study, 6/12 patients who became inactive during follow-up also showed normalization of AA5A levels. AECA and ACLA were detected in 54% (13/24) and 12% (3/24) of the AA5A-positive patients, respectively. Our results show that a significant proportion of TA patients have AA5A, which exhibit an association with AECA and because they have a correlation with disease activity thus appear to be involved in the disease pathogenesis.

T cell Vbeta repertoires in childhood vasculitides

Superantigens (SAgs) are potent stimulators of T cells bearing specific Vbeta T cell receptors (TCR) and may play a role in the aetiopathogenesis of systemic vasculitis, although this remains contentious. To investigate the possible aetiological role of SAgs, this study examined peripheral blood T cell Vbeta repertoires in children with systemic vasculitis. FACS analysis of 17 different peripheral blood T cell Vbeta families was performed in 20 healthy control children, 27 disease control children with nonvasculitic inflammatory disease, 25 children with primary systemic vasculitis, six patients with Kawasaki disease (KD) and six patients with Henoch-Schönlein purpura (HSP). There was a significantly increased variance of CD4 Vbeta12 and Vbeta17, and CD8 Vbeta1 in the primary systemic vasculitis group compared to control and disease controls. Moreover, 80% of the primary systemic vasculitis children had one or more CD4 Vbeta expansions or deletions, compared with 30% of controls (P < 0.002), and 37% of the disease controls (P < 0.002). In the KD group, the mean percentage of CD4 Vbeta2 T cells was higher than in controls or disease controls. In the HSP group, there was no consistent skewing of the T cell Vbeta repertoire. We have observed changes in the T cell Vbeta repertoire in children with vasculitis over and above those observed in disease controls. While these data provide impetus for further research into this contentious field, they do not resolve unequivocally the question of the role of SAgs in childhood vasculitic syndromes.

Vasculitis in childhood

Vasculitis is an important diagnostic consideration in the child with prolonged fever, unexplained pains, new neurologic findings, or other persistent and troubling signs of inflammation. As long as the etiology of vasculitis remains unknown, reliance upon imperfect diagnostic criteria is likely to remain the state of the art. Nonetheless, anti-inflammatory and immunosuppressive therapy is highly effective in speeding resolution of systemic inflammation and reducing long-term complications. The care, experience, and acumen of the treating physician thus remain the gold standard for diagnosing and treating pediatric vasculitides. In all cases this begins with a high level of suspicion in the primary care physician.

Vasculitis in childhood

Inadequate understanding of the pathogenesis and etiology of vascular inflammation continues to hinder progress in the diagnosis and treatment of pediatric vasculitis. The greatest amount of work is being done in the most common vasculitides of childhood, including Kawasaki disease and Henoch-Schönlein purpura. Discussion of rarer types of vasculitis, on the other hand, such as antineutrophil cytoplasmic antibody-positive small vessel diseases, is largely restricted to case reports. Most aspects of the care of children with Wegener granulomatosis and microscopic polyangiitis are derived by extrapolating from data about adults. Virtually no data are available concerning ways in which these diseases may be different in children.