igg4-related disease ( igg4-rd ) is an emerging fibro - inflammatory condition known to involve potentially every organ system in the body . in view of its recent recognition as a nosological entity ,
the approach to diagnosis , therefore , necessarily involves the exclusion of common infectious , neoplastic and inflammatory mimickers , principally through pathological evaluation of biopsy specimens .
histological features characteristic of igg4-rd are shared by seemingly unrelated organs and include storiform fibrosis , obliterative phlebitis , tissue eosinophilia , and a lymphoplasmacytic infiltrate in which the ratio of igg4- to igg - positive plasma cells generally exceeds 0.40 .
substantial overlap in the types of organ involvement and histopathological features occur in igg4-rd and vasculitides associated with antineutrophil cytoplasmic antibodies ( anca ) , that is , granulomatosis with polyangiitis ( gpa ) , microscopic polyangiitis ( mpa ) , and eosinophilic granulomatosis with polyangiitis ( egpa)collectively termed anca - associated vasculitis ( aav ) . as examples , different forms of aav have predilections for affecting the orbital regions , sinuses , lungs , kidneys , meninges , and even the pituitary gland , all of which are known to be affected by igg4-rd , as well .
moreover , the aav can be associated with both peripheral and tissue eosinophilia , and aav rivals igg4-rd in its ability to cause igg4-positive plasma cell infiltration into involved organs .
elevation of serum igg4 concentrations has been considered a useful biomarker of igg4-rd , but broader experience in managing these patients has revealed the shortcomings of this measurement as a diagnostic tool .
conversely , a substantial proportion of patients with clinical presentations and organ biopsies consistent with igg4-rd have normal serum igg4 concentrations .
in contrast , the finding of a positive anca assay for either the proteinase 3 ( pr3 ) or myeloperoxidase ( mpo ) antigen is generally regarded as a highly specific finding in favor of an aav diagnosis .
recent reports , however , have raised the possibility that some patients with igg4-rd are anca positive , thus suggesting reconsideration of the role of anca in the diagnostic workup . in the present work ,
we describe a patient with concomitant biopsy - proven igg4-rd and gpa in whom we demonstrated anti - pr3 anca of the igg4 subclass .
we also review the literature to provide tools for interpreting anca positivity in igg4-rd patients . to this purpose
, we searched the entire pubmed and google scholar online databases for variable combinations of the following terms :  anca ,  
igg4 ,   igg ,   igg4-related disease ,   granulomatosis with polyangiitis ,  and  vasculitis . 
we then considered all the written - english reports of igg4-rd patients with evidence of a positive anca titer .
ethical approval was not necessary because all diagnostic and therapeutic procedures were performed in accordance with international guidelines for the management of gpa and igg4-rd .
a 51-year - old nonatopic woman was referred to our outpatient clinic for swelling of the left lacrimal gland , left orbital pain radiating to the left side of her face , mild proptosis , and redness of the left eye ( fig .
1a ) . she also complained of a mild discomfort in the infra - scapular region .
her medical history was significant for arterial hypertension , gastroesophageal reflux disease , and chronic bronchitis .
gadolinium - enhanced magnetic resonance imaging ( mri ) of the brain and orbits disclosed an enlarged left lacrimal gland surrounded by an inflammatory tissue in contiguity with the lateral and superior rectus muscles ( fig .
the inflammatory tissue showed intense 18f - fluorodeoxyglucose ( 18f - fdg ) uptake on positron emission tomography / computed tomography ( pet / ct ) study ( fig .
1e ) . both the erythrocyte sedimentation rate ( 43  mm / h ; normal < 20 ) and total ige ( 1798  iu / ml ; normal < 100 ) were elevated , but the c - reactive protein and tests of renal , thyroid , and liver function were within normal range .
an assay for antinuclear antibodies was positive in a titer of 1:160 ( homogenous pattern ) but assays for rheumatoid factor , antibodies to double - stranded dna , thyroperoxidase , and thyroglobulin were negative .
serum igg4 level was 253  mg / dl ( normal < 135  mg / dl ) .
the preoperative chest radiograph , however , showed multiple oval lung lesions in the right lung , raising concern for the possibility of malignancy ( fig .
a chest ct scan confirmed 2 round - shaped nodules and 1 cavitary mass in the right lung , and revealed a paravertebral lesion on the right side of the t5 and t6 vertebrae ( fig .
all of these lesions demonstrated intense 18f - fdg uptake on pet / ct ( fig .
( c ) a gadolinium enhanced magnetic resonance imaging showing left scleritis ( arrowheads ) and enlarged left lacrimal gland surrounded by an inflammatory tissue in contiguity with the lateral and superior rectum muscles ( arrow ) .
( e ) 18f - fluorodeoxyglucose uptake in the left periorbital tissue on positron emission tomography scan .
( b  f ) clinical and radiological remission 6 months after methylprednisolone pulses and rituximab ( arrows ) .
( a , d , g ) thoracic ct scan and ( b ) chest radiograph showing right lung masses ( arrows ) , 1 of them ( g ) with cavitation ( arrowhead ) , all showing intense 18f - fdg uptake on pet / ct scan ( e , g ) ( arrowheads ) .
( h ) thoracic ct scan revealing a right paravertebral mass with 18f - fdg uptake on pet / ct scan ( arrowheads ) .
disappearance of lung masses 6 months after rituximab on radiograph ( c ) and pet / ct scan ( f ) . 18f - fdg = 18f - fluorodeoxyglucose , pet / ct = positron emission tomography / computed tomography .
examination of the left lacrimal gland tissue revealed areas of storiform fibrosis with abundant igg4-positive plasma cells ( igg4+/igg+ plasma cells ratio > 40% ) , consistent with the suspicion of igg4-related dacryoadenitis ( fig .
neutrophilic infiltration , vasculitis , granulomatous inflammation , and necrosis were all not present in the lacrimal gland , examined in multiple sections .
however , the lung tissue showed chronic granulomatous inflammation , leukocytoclastic vasculitis , and areas of geographic necrosis , features highly suggestive of gpa ( fig . 4a 
the patient 's serum tested positively for anca by both immunofluorescence ( cytoplasmic anca pattern ) and enzyme immunoassay , with specificity for pr3 ( 423 au ; normal value < 20 au ) .
the anca appeared to consist of both the igg1 and igg4 subclasses ( fig . 3a and b ) .
in addition , the counts of circulating plasmablasts  defined as cd19 + cd20cd27 + cd38 + bright cells on flow cytometry  were dramatically increased ( 50,000  cells / ml ; normal < 635  cells / ml ) .
the patient was started on prednisone ( 1  mg / kg ) followed by 2 infusions of rituximab 1000  mg , administered 15 days apart .
immunofluorescence studies , flow cytometry analysis , and histological evaluation of the left lacrimal gland affected by igg4-related disease .
( a and b ) immunofluorescence assays performed on commercially available slides ( nova lite ancakit / substrated slides  inova diagnostic san diego , ca ) demonstrates antineutrophil cytoplasmic antibodies of igg1 ( a ) and igg4 ( b ) subclass in the patient 's serum ( serum dilution 1:20 ; secondary anti - igg1 ( mouse antihuman igg1-alexa fluor 488 conjugate  thermofisher , st waltham , ma ) and anti - igg4 ( mouse antihuman igg4-fitc conjugate 
alpha diagnostics international , san antonio , tx ) antibodies dilution 1:50 and 1:20 , respectively ) .
( c  f ) histological examination of the left lacrimal gland reveals areas of storiform fibrosis ( c  asterisks ) , and lymphoplasmocytic infiltrate ( d  arrows ) without granulomas or vascultis .
immunohistochemistry for total igg ( e ) and igg4 ( f ) shows abundant igg4 positive plasma cells with an igg4/igg ratio > 40% .
( g ) circulating plasmablasts ( cd19 + cd20cd27 + cd38bright cells ) are expanded at disease onset and diminish following b cell depletion therapy with rituximab .
geographic necrosis ( a  arrowheads ) , granulomas ( c  circles ) with giant cells ( c  arrows ) , and necrotizing vasculitis ( e  circle ) with extravasation of red blood cells and neutrophils ( e  arrows ) . immunohistochemistry ( b , d , f ) reveals igg4 positive plasma cells infiltrate in a , c , and e. six months later , the orbital and lung lesions had resolved .
in particular , a whole body pet / ct scan showed normalization of the 18f - fdg uptake findings ( figs .
follow - up ophthalmologic and orbital mri evaluations confirmed inactive scleritis and substantial regression of the orbital lesion , respectively ( fig .
lung masses were no longer evident on either chest radiography or ct ( fig . 2c ) .
laboratory and serological studies revealed normalization of the inflammatory markers and of the serum igg4 ( 67  mg / dl ) , normalization of the circulating plasmablast level ( 350  cells / ml ) ( fig .
3 g ) , a negative pr-3 anca assay , and marked reduction of serum ige levels ( 200  iu / ml ) .
we identified 9 other reports of patients with igg4-rd and positive anca in the english literature ( tables 1 and 2 ) .
five cases had biopsy - proven igg4-rd and were included in our analysis ( table 1 ) .
the remaining 4 cases , in whom igg4-rd was diagnosed presumptively ( based on elevated serum igg4 levels and compatible organ involvement ) , are listed separately in table 2 but not discussed further , because they lacked histopathological investigation .
cases reported in the literature of patients with biopsy - proven igg4-rd and positive anca .
the male to female ratio of biopsy - proven igg4-rd cases was 4:2 , with a median age at diagnosis of 59 years ( range 3873 years ) ( table 1 ) .
organs involved by igg4-rd were the lacrimal glands and the periorbital tissue ( 2 cases each ) , the hypophysis , the mediastinum , the salivary glands , the meninges , the nose , and the paranasal sinuses ( 1 case each ) .
four out of 6 patients had also histological evidence of concomitant aav in other organs , namely neutrophilic abscesses , leukocytoclastic vasculitis , fibrinoid necrosis , granulomatous inflammation , and crescentic glomerulonephritis .
organ involvement of aav included the lung ( 3 cases ) , the skin and the kidney ( 2 cases each ) , and the peripheral nerves and the inner ear ( 1 case each ) .
biopsies of organs involved by aav were obtained in 4 cases and histology revealed leukocytoclastic vasculitis ( 3 cases ) , and granulomas and crescentic glomerulonephritis ( 1 case each ) . among these 4 patients , 1
was diagnosed with egpa based on a history of long - standing asthma , multiple mononeuritis , peripheral blood eosinophilia , anca positivity with a specificity for mpo , and histological evidence of cutaneous leukocytoclastic vasculitis with abundant eosinophils .
two patients were diagnosed with aav in the absence of specific findings to diagnose gpa , mpa , or egpa definitively .
the median c - reactive protein at diagnosis was 26.2  mg / dl ( range 21167  mg / dl ) .
the erythrocyte sedimentation rate , measured in 3 cases , ranged from normal to 100  mm / h .
serum igg4 concentration was increased in all 6 patients ( median 298  mg / dl ; range 143470  mg / dl ) .
all patients also had positive anca , 3 with a specificity for mpo , 2 with pr-3 specificity , and 1 with unknown specificity .
early recurrence after steroid tapering or partial clinical responses , however , prompted the addition of second - line immunosuppressive agents in all 6 cases .
ohno et al and alexandraki et al , for instance , added azathioprine to oral prednisolone at disease relapse but did not observe any further benefit .
paulus at al achieved prompt clinical remission in a patient with scleritis and orbital myositis by combining methotrexate and intraocular triamcinolone to oral prednisone . in the case reported by hanioka et al
, prednisolone led to a reduction of lacrimal gland swelling , but peripheral neuropathy improved only with intravenous immunoglobulins and methyprednisolone pulses .
similarly , intravenous cyclophosphamide and methylprednisolone pulses were required in addition to oral prednisone in order to prevent renal failure in a patient with rapidly progressive glomerulonephritis .
our results indicate that patients with biopsy - proven igg4-rd can also have positive anca with specificity for either mpo or pr3 , with or without the concomitant presence of an overt aav .
this finding is supported by a growing body of literature and suggests caution in the interpretation of anca positivity , a finding traditionally viewed as highly specific for aav if confirmed by both immunofluorescence and enzyme immunoassay .
this process is based , first , upon the confirmation of mpo or pr3 specificity through either elisa or chemiluminescent assays .
the specificity of immunofluorescence for anca testing is suboptimal , as immunofluorescence assays are associated with positive results in a number of conditions other than small vessel vasculitides .
most anca target antigens other than mpo or pr3 ; that is , they target an array of granulocyte or monocyte granule components and often have multiple or unknown specificities .
once confirmation by enzyme immunoassay or chemiluminescence is obtained ; however , a positive anca result in and of itself is not diagnostic of aav but rather requires clinical - pathological correlation and histological confirmation .
the case we describe here is emblematic in this sense because , based on the sole assumption that pulmonary pseudo - tumors are well - described manifestations of igg4-rd , the histological evidence of igg4-related dacryoadenitis appeared sufficient for diagnostic purposes and did not require confirmation with a lung biopsy . because cavitary lesions are not typical of igg4-rd , however , we proceeded to lung biopsy , which ultimately led to the concomitant diagnosis of aav
. the fact of a paravertebral thoracic mass in our patient further complicated the differential diagnosis , as it is an atypical manifestation of either gpa or igg4-rd . in summary , the finding of a positive anca  even with a specificity for pr3should not lead to premature closure of the diagnostic evaluation , particularly if the pattern of organ involvement is not strictly typical of aav . in our patient ,
as described in our aggregate analysis , this was actually the case of 3 patients with biopsy - proven igg4-rd and positive anca who developed clinical manifestations of aav shortly after the diagnosis .
indeed , both mpo- and pr3-anca of patients with aav have been previously shown to induce respiratory burst , calcium flux , and degranulation of neutrophils , thus directly contributing to the pathophysiology of aav .
igg4 anca are known to elicit the vigorous generation of reactive oxygen species in vitro , comparable to those elicited by igg3 anca , and greater than those induced by igg1 anca .
the anca in aav are most often igg1 and igg4a finding that we confirmed in our patient .
it is therefore tempting to speculate that the prominent igg1 and igg4 production that is characteristic of igg4-rd might foster the development of aav in some patients with an appropriate genetic background .
indeed , the abundant igg4 positive plasma cell infiltrate that we found in gpa lesions may further support this hypothesis .
igg4-rd in patients with positive anca was limited to the head and neck , and did not involve other commonly affected organs , such as the lung , the pancreas , the biliary tree , and the retroperitoneum .
in contrast , aav in patients with established igg4-rd presented with systemic manifestations beyond the ear / nose / throat region , consistent with the notion of that anca positivity is more common in the former clinical setting than in the latter .
these observations suggest that patients with igg4-rd and positive anca might be more at risk of developing a systemic form of aav
. indeed , head and neck manifestations of igg4-rd are typically anca negative raising the possibility that anca in these patients might sustain an underlying vasculitic process rather than being primarily linked to igg4-rd
. additional cases and a longer follow - up are needed in order to confirm this hypothesis .
table 2 describes the clinical characteristics of 4 additional patients with positive anca and a diagnosis of possible igg4-rd with meningeal ( 3 cases ) and retroperitoneal ( 1 case ) involvement .
anca specificity was confirmed by elisa in all 4 patients , but no diagnostic procedures were performed in these patients . for these reasons , despite serum igg4 increase , we did not include these cases in our aggregate analysis .
however , as opposite to pachymeningeal involvement , which might occurs in up to 60% of patients with gpa , retroperitoneal fibrosis is an uncommon manifestation of aav .
therefore , while those cases of anca positive pachymeningitis are more likely patients with gpa , anca positive retroperitoneal fibrosis with elevated serum igg4 could represent a case of igg4-rd .
patients with positive anca and retroperitoneal fibrosis , indeed , have been already reported in the literature , raising the possibility of a novel immune - mediated condition associated with retroperitoneal inflammation .
histological findings of the retroperitoneal tissue , however , have not been reported in these case series , thus making impossible to drive definitive conclusions .
in conclusion , the present work demonstrates that anca positivity in patients with biopsy - proven igg4-rd should prompt the exclusion of a concomitant vasculitic process .
in addition , a positive anca does not exclude the diagnosis of igg4-rd absolutely , particularly in cases with head and neck involvement that is characteristic of igg4-rd . the hypothesis that anca might predict the development of aav in patients with igg4-rd deserves larger case series with a longer follow - up .
confirmation through immunoenzymatic assays of the anca specificity , clinical - pathological correlation , and histopathological evaluation remain crucial steps for the differential diagnosis between aav and igg4-rd .
the authors thank dr raffaella milani ( immunohematology and transfusion medicine unit , irccs san raffaele scientific institute ) for performing flow cytometry studies .
 abstractbackground : igg4-related disease ( igg4-rd ) is a fibroinflammatory condition characterized by serum igg4 elevation and tissue infiltration of igg4-positive plasma cells . 
 substantial overlap between igg4-rd and antineutrophil cytoplasmic antibodies ( anca)-associated vasculitides ( aav ) exists in terms of organ involvement and histopathological features . 
 a positive anca assay is regarded as a highly specific finding in favor of an aav , and generally influences away from a diagnosis of igg4-rd . 
 recent reports , however , have raised the possibility that some patients with igg4-rd are anca positive , thus suggesting reconsideration of the role of anca in the diagnostic workup . in the present work , 
 we describe the first case of concomitant biopsy - proven igg4-rd and granulomatosis with polyangiitis ( gpa ) , demonstrating antiproteinase 3 ( pr3 ) anca of the igg4 subclass in the patient 's serum . 
 we also review the literature in order to provide clinicians with tools for interpreting anca positivity in igg4-rd patients.case summary : a 51-year - old woman was referred for left exopthalmos due to lacrimal gland enlargement and increased serum igg4 concentration . 
 igg4-rd was suspected and further imaging studies disclosed multiple pulmonary masses in the right lung . 
 histological analysis of the left lacrimal gland was diagnostic for igg4-rd , but lung biopsy showed typical features of gpa . 
 anca assay was positive for anti - pr3 antibodies . 
 further immunofluorescence studies demonstrated anti - pr3 antibodies of igg1 and igg4 subclass . 
 treatment with rituximab induced swift remission of both igg4-rd and gpa manifestations . 
 we identified 9 other reports of patients with igg4-rd and positive anca in the english literature , 5 cases with biopsy - proven igg4-rd and 4 cases in whom igg4-rd was diagnosed presumptively . 
 four patients had also histological evidence of concomitant aav.conclusion:the present work demonstrates that anca positivity in patients with biopsy - proven igg4-rd should prompt the exclusion of a concomitant vasculitic process ; a positive anca does not exclude the diagnosis of igg4-rd ; confirmation through immunoenzymatic assays of the anca specificity , clinical - pathological correlation , and histopathological evaluation remain crucial steps for the differential diagnosis between aav and igg4-rd . 