Neuropathies périphériques au cours des maladies de système : partie I (connectivites et granulomatoses)

Systemic diseases (connective disease, granulomatosis) may be associated with peripheral neuropathies. The diagnosis can be complex when the neuropathy is the presenting manifestation of the disease, requiring close collaboration between neurologists and internists. Conversely, when the systemic disease is already known, the main question remaining is its imputability in the neuropathy. Regardless of the situation, the positive diagnosis of neuropathy is based on a systematic and rigorous electro-clinical investigation, specifying the topography, the evolution and the mechanism of the nerve damage. Certain imaging examinations, such as nerve and/or plexus MRI, or other more invasive examinations (skin biopsy, neuromuscular biopsy) enable to specify the topography and the mechanism of the injury. The imputability of the neuropathy in the course of a known systemic disease is based mainly on its electro-clinical pattern, on which the alternatives diagnoses depend. In the case of an inaugural neuropathy, a set of arguments orients the diagnosis, including the underlying terrain (young subject), possible associated systemic manifestations (inflammatory arthralgias, polyadenopathy), results of first-line laboratory tests (lymphopenia, hyper-gammaglobulinemia, hypocomplementemia), autoantibodies (antinuclear, anti-native DNA, anti-SSA/B) and sometimes invasive examinations (neuromuscular biopsy).     

IgG4-related periaortitis/periarteritis: An under-recognized condition that is potentially life-threatening

Abstract

Periaortitis and periarteritis are one of the clinical features of IgG4-related disease. Such vascular manifestations are reported to be present in 10–30% of overall IgG4-related disease, and they may also appear as an isolated lesion of IgG4-related disease. As other types of large vessel vasculitis, IgG4-related vasculitis may cause significant clinical consequences. On the other hand, the diagnosis of IgG4-related periaortitis/periarteritis seems to have been made on the basis of different diagnostic criteria in reported studies; thus far, difficulty seems to be present in assessing the true frequency of the disease as well as determining the optimal therapeutic strategy. In this review, in addition presenting the clinical and pathological features of IgG4-related periaortitis/periarteirtis, we would like to discuss on what kind of points should be resolved for the better understanding of vascular involvement of IgG4-related disease in terms of diagnosis and treatment.     

A case of ANCA-negative renal small-vessel vasculitis with tubulointerstitial infiltration of IgG4-positive plasma cells

A 62-year-old male patient presented with progressive renal dysfunction for 2 months. He had elevated serum C-reactive protein and IgG4 levels with absence of anti-neutrophil cytoplasmic antibodies. A renal biopsy showed severe tubulointerstitial nephritis (TIN) with extensive infiltration of IgG4-positive plasma cells, suggesting a diagnosis of IgG4-related kidney disease (IgG4-RKD). However, the identification of a few crescentic glomeruli and necrotizing vasculitis of an interlobular artery lead to a diagnosis of renal small-vessel vasculitis. This case indicates that a careful examination is required to distinguish between IgG4-RKD and TIN caused by renal small-vessel vasculitis.     

Peripheral T-cell lymphoma that developed during the follow-up of IgG4-related disease

IgG4-related disease is a recently recognized fibroinflammatory disorder characterized by extensive IgG4-positive plasma cell and lymphocyte infiltration of various organs. The pancreatic manifestation of IgG4-related disease is called autoimmune pancreatitis (AIP), in which autoimmune mechanisms are likely involved. On the other hand, some autoimmune and chronic inflammatory disorders, such as Sj?gren's syndrome and rheumatoid arthritis, are associated with increased risks of non-Hodgkin lymphoma (NHL). There have been a few reports of cases with IgG4-related disease that had subsequently developed NHL, however, all of them suffered from B-cell lymphoma. We describe the first case of NHL, compatible with a subtype of peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), which arose in IgG4-related sclerosing cholangitis. As patients with IgG4-related disease may be at an increased risk of developing NHL, such presentation during the follow-up of IgG4-related disease should be carefully scrutinized to exclude NHL.     

Autoimmune reactions in patients with M-component and peripheral neuropathy.

A study of 17 patients with autoimmune axonal or demyelinating peripheral neuropathy in combination with M-component is described. The M-component was associated with MGUS (monoclonal gammopathy of undetermined significance) in 12 patients, CLL in one patient, WaldenstrÖm's disease in one patient, and myeloma in three patients. Immunohistological examination with direct and indirect fluorescence showed binding of antibodies to nerve structures of the same class and light chain as seen in the M-component. In five cases of IgM M-component, the demyelinating neuropathy was caused by binding of the IgM M-protein and complement C3b to myelin-associated glycoproteins (MAG). In 12 cases with axonal neuropathy, binding of IgG to the connective tissue of the peri- and endoneurium was found in 50% of cases, IgM in five cases, and IgD in one case. None of the patients had central nervous system (CNS) symptoms. The clinical and therapeutic difficulties are discussed; only two patients with an acute course responded to immunosuppression. A marked co-expression of other autoimmune phenomena is interpreted in the light of cross-reactions between the autoantibody and similar tissue autoantigens.     

Diagnosis and treatment of primary Sjögren syndrome-associated peripheral neuropathy: a six-case series

Objectives

The clinical and therapeutic aspects of primary Sjögren syndrome (PSS) in patients with peripheral neuropathy were analyzed and the specifics of individual case studies are discussed.

Methods

We retrospectively studied six patients (four women, two men; mean age 64.5 years) presenting with PSS with peripheral neurological involvement over a five-year period (2008–2012). All patients had neurological examinations, including nerve conduction studies, somatosensory evoked potentials, and sural nerve biopsies. Treatment regimens included corticosteroids, intravenous gammaglobulin, or immunosuppressive treatment.

Results

Peripheral neuropathy was observed in six (7.9 %) of 76 patients with SS as the underlying disease; three were cases of multiple mononeuropathy, two cases had sensory ataxic neuropathy, one of which was autonomic neuropathy, and one case was diagnosed as painful sensory neuropathy without sensory ataxia. Four of the six patients were diagnosed with SS after the onset of neurological symptoms. Individual peripheral neuropathies had distinct neurological, electrophysiological, and pathological characteristics. The effect of steroids and intravenous gammaglobulin differed depending on the case.

Conclusions

In PSS patients, a precise diagnosis is important, because the therapeutic strategy and response varies depending on the type of neuropathy. In clinical practice, it is important to consider a diagnosis of SS when patients present with peripheral neuropathy.     

Pseudoclaudication as a manifestation of diabetic neuropathy.

We present the case of a 64-year-old male Type 1 diabetic patient with painful diabetic neuropathy masquerading as intermittent claudication. Examination of the peripheral circulation (both arterial and venous) was normal. An MRI scan excluded lumbar spinal stenosis and nerve root compression as the cause of claudication. The case suggests that, in the absence of other identifiable causes and in the presence of peripheral diabetic neuropathy, "intermittent claudication" may be due to the neuropathy itself.     

A clinical,electrophysiological, and pathological study of neuropathy in rheumatoid arthritis

Neuropathy in rheumatoid arthritis (RA) may result secondary to entrapment, vasculitis, and drug toxicity. We aimed to study clinical and electrophysiological neuropathy and pathological changes in sural nerve in patients with RA. One hundred eight patients of RA, fulfilling American College of Rheumatology 1987 criteria (mean age, 45.83 years; M/F 1:3, 80.3% seropositive) were examined clinically and electrophysiologically for evidence of peripheral neuropathy. Sural nerve biopsies were performed in the involved cases. In all RA patient medications, disease activity, results of blood tests, and X-rays of affected joints were recorded. Twenty-three patients complained of paresthesias in the extremities. Vibration sensations were decreased in 9, and tendon reflexes were decreased or absent in 28 patients. Sixty-two (57.4%) patients had electrophysiologic evidence of neuropathy. Of these 53 (85.5%) patients had pure sensory or sensory motor axonal neuropathy (mononeuritis multiplex, n = 7), while 9 (14.5%) had demyelinating neuropathy (chronic inflammatory demyelinating polyneuropathy, n = 1). Carpal tunnel syndrome was seen in 11 (10.1%) patients (associated with neuropathy in 6). Of 23 sural nerve biopsies available, perineurial thickening (n = 5, amyloid deposits n = 4), perivascular lymphomononuclear cell infiltrate (n = 4), loss of myelin fibers (n = 2), and necrotizing vasculitis (n = 1) were found. Clinically, however, seven patients had evidence of cutaneous vasculitis. Comparing the clinical characteristics of the patients with or without electrophysiological neuropathy, absence of deep tendon jerks (p < 0.005) and presence of extra articular manifestations (p < 0.01) were conspicuous in the neuropathic group. There was no relation of neuropathy with the duration of RA, seropositivity, joint erosions, joint deformities, prior disease-modifying anti-rheumatic drugs or glucocorticoid intake, and 28-joint disease activity score. Neuropathy in RA was mostly subclinical and predominantly axonal. Pathologically, neuropathy secondary to amyloid infiltration was second only to vasculitic neuropathy. Absence of deep tendon jerks and presence of vasculitis were more commonly observed in patients with neuropathy.     

Cranial and peripheral neuropathy in rheumatoid arthritis with special emphasis to II,V, VII,VIII and XI cranial nerves

Background: Cranial neuropathy in rheumatoid arthritis (RA) is relatively rare compared to the frequently reported peripheral neuropathy. Methods: We investigated the occurrence of subclinical cranial and peripheral nerve involvement in 55 patients with RA. Results: Patients had a mean age of 43.1 years and a mean duration of illness of 6.4 years. All patients presented with electrophysiological findings suggestive of peripheral neuropathy. In addition, 69.1% of them had entrapment neuropathies, in which carpal tunnel syndrome was the most common (54.6%). Sensorimotor neuropathy at sites other than usual entrapment sites was diagnosed in 70.9%, while bilateral distal sensory neuropathy in lower limbs was identified in 29.1%. Among cranial nerves examined, optic and vestibulocochlear neuropathies were common (29.1% of eyes and 40% of ears examined). Spinal accessory neuropathy was reported in 21.8% of records. Neither facial nor trigeminal nerves were affected. Electrophysiological characteristics of neuropathies were indicative of axon loss. Significant association was identified between neuropathy and patients’ ages (P < 0.01), duration of the illness (P < 0.001), presence of rheumatoid nodules (P < 0.001) and disease stages (P < 0.001). Conclusions: Our results indicate that cranial and non‐compressive neuropathies are not uncommon in RA. This extends the pathologic disease spectrum. We do not confirm, but suggest the contribution of chronic immune‐mediated vasculitis and/or neurotoxicity in RA neuropathies. Of clinical importance, subclinical neuropathy may never progress and/or be of clinical significance, which contradicts that of comparable diseases, such as systemic lupus erythematosus. Advances in genetics implicate a complex immune genetics which controls susceptibilities and adaptive molecular mechanisms as a culprit of phenotypical heterogenicity among related diseases.     

IgG4-related disease as a variable-vessel vasculitis: A case series of 13 patients with medium-sized coronary artery involvement

IntroductionIgG4-related disease (IgG4-RD) is a systemic autoimmune fibroinflammatory disease that can affect multiple organ systems. Although large-vessel vasculitis is a well-recognized manifestation of IgG4-RD, this condition is generally not regarded as a vasculitis. We aimed to describe coronary artery involvement (CAI), a vascular distribution about which little is known in IgG4-RD.Material and methodsPatients with IgG4-related CAI were identified from a large, prospective IgG4-RD cohort. CAI was confirmed by imaging evidence of arterial or periarterial inflammation in any coronary artery. We extracted details regarding demographics, features of IgG4-RD, and manifestations of CAI.ResultsOf 361 cases in the cohort, 13 (4%) patients had IgG4-related CAI. All were male and all had highly-elevated serum IgG4 concentrations, with a median value of 955 mg/dL (interquartile range [IQR]: 510–1568 mg/dL; reference: 4–86 mg/dL). Median disease duration at the time of CAI diagnosis was 11 years (IQR: 8.23–15.5 years). Extensive disease in the coronary arteries was the rule: all three major coronary arteries were involved in 11 patients (85%). The coronary artery manifestations included wall thickening or periarterial soft tissue encasement (85%), stenosis (69%), calcification (69%), and aneurysms or ectasia (62%). Five patients (38%) had myocardial infarctions, 2 (15%) required coronary artery bypass grafting, and 2 (15%) developed ischemic cardiomyopathy.DiscussionCoronary arteritis and periarteritis are important manifestations of IgG4-RD, which should be regarded as a variable-vessel vasculitis that is among the most diverse forms of vasculitis known. Potential complications of CAI include coronary artery aneurysms, myocardial infarction, and ischemic cardiomyopathy.     

148例急性非创伤性肢体无力性疾病的诊断

目的探讨急性非创伤性肢体无力性疾病的病因,为临床及早治疗提供依据。方法对148例以急性非创伤性肢体无力为首发症状患者的临床资料进行回顾性分析,总结其病因及治疗结果。结果出院诊断为脊髓疾病42例,周围神经病38例,脑部疾病32例,神经肌肉接头疾病10例,低钾型麻痹10例,多发性肌炎6例,癫痫持续状态6例,系统性疾病4例;痊愈100例（67．5％）,症状显著改善30例、好转1O例（94．6％）,症状无明显变化6例,死亡1例（HIV周围神经病）,自动放弃治疗1例（高颈段脊髓压迫症）。结论具备以急性非创伤性肢体无力为首发症状的疾病谱很广,尽早明确诊断并给予病因治疗可减少并发症和后遗症、改善患者生活质量。     

IgG4相关性肺疾病1例及文献复习

目的提高对IgG4相关性肺疾病的临床特征、胸部影像学和病理组织学的认识。方法对1例经病理证实的IgG4相关性肺疾病的临床资料进行分析,并结合文献进行回顾总结。结果患者男,62岁,以胸腔积液起病,在外院先后行胸膜活检、胸腔镜肺活检等均未能明确诊断,后至我院行CT引导下经皮肺穿刺活检术,结果示活检组织内纤维组织增生伴淋巴细胞、浆细胞等炎症细胞浸润,免疫组化示大量浆细胞(+),IgG4阳性,浆细胞最密集计数约为40个/高倍视野,血清IgG4浓度示4.07 g/L(0.03 g/L~2 g/L)。诊断IgG4相关性肺疾病,给予糖皮质激素治疗,2个月后复查胸部CT示肺部病灶较前局部吸收、好转。结论IgG4相关性疾病是一种累及多器官、以血清IgG4水平升高、组织IgG4阳性浆细胞浸润为特点的淋巴浆细胞病。目前国内IgG4相关性肺疾病的报道很少,报道这一病例并进行文献复习有助于提高对IgG4相关性肺疾病的认识。     

Peripheral neuropathy in two patients with rheumatoid arthritis receiving infliximab treatment

Antitumor necrosis alpha agents have been successfully used for the treatment of rheumatoid and seronegative arthritis, Crohn’s disease, psoriasis, and severe cases of vasculitis. Several side effects have been observed in patients receiving these agents including hypersensitivity reactions, infections, drug-induced lupus, or demyelinating syndromes. The presence of peripheral neuropathy has been reported only in isolated cases. We describe two cases of peripheral neuropathy which occurred in patients with rheumatoid arthritis receiving infliximab treatment, one with multifocal motor neuropathy with conduction block and another with axonal sensory polyneuropathy, reversed upon discontinuation of infliximab and intravenous gammaglobulin treatment.     

IgG4-Related Disease and Hypertrophic Pachymeningitis

Hypertrophic pachymeningitis (HP) is an inflammatory condition in which the dura mater of the cranium or spine becomes thickened, leading to symptoms that result from mass effect, nerve compression, or vascular compromise. The differential diagnosis of HP includes immune-mediated conditions such as rheumatoid arthritis and vasculitis, malignancies, and infections. Many times, no diagnosis is reached; in such cases, the disease has been described as idiopathic HP. IgG4-related disease (IgG4-RD) is a recently described inflammatory condition known to cause tumefactive lesions at myriad anatomical locations. Both IgG4-RD and idiopathic HP share similar demographics, histopathology, and natural history. We hypothesized that IgG4-RD is a common cause of idiopathic HP.To investigate this hypothesis, we identified all pathology specimens diagnosed as noninfectious HP during 25 years at our institution. Fourteen cases had stained slides and paraffin blocks to permit review of the original hematoxylin and eosin stained slides as well as immunostaining of cell blocks. Recently published consensus guidelines describing characteristic histopathology and the necessary quantity of IgG4+ plasma cell infiltrate were used to diagnose IgG4-RD.Four cases (66.6%) that had been regarded previously as representing idiopathic HP were diagnosed as IgG4-RD; of all the reviewed cases, IgG4-RD represented 29% of cases. Of the remaining cases, 3 cases were associated with granulomatosis with polyangiitis (GPA), 2 with lymphoma, and 1 each with rheumatoid arthritis, giant cell arteritis, and sarcoidosis. Two of the cases could not be diagnosed more precisely and were classified as undifferentiated HP. Clinical history, serologic tests, cerebrospinal fluid studies, and radiology alone could not identify the cause of HP. Rather, biopsy with histopathology and immunostaining was necessary to reach an accurate diagnosis. Significant IgG4+ plasma cell infiltrates were observed in rheumatoid arthritis, granulomatosis with polyangiitis, and lymphoma, underscoring the importance of histopathology in making the diagnosis of IgG4-RD.This case series demonstrates that IgG4-RD may be the most common etiology of noninfectious HP and highlights the necessity of biopsy for accurate diagnosis.Abbreviations: ANCA = antineutrophil cytoplasmic antibodies, CNS = central nervous system, CSF = cerebrospinal fluid, CT = computed tomography, GPA = granulomatosis with polyangiitis, HP = hypertrophic pachymeningitis, HPF = high-power field, IgG4-RD = IgG4-related disease, MRI = magnetic resonance imaging, WBC = white blood cell     

Neuropathies périphériques au cours des maladies de système : partie II (vascularites)

Primary systemic vasculitides, mainly of the small and medium-sized vessels, are frequently associated with peripheral neuropathies. When the disease is already known, the appearance of a neuropathy should suggest a specific injury, especially when associated with other systemic manifestations. Conversely, when neuropathy is inaugural, close collaboration between neurologists and internists is necessary to reach a diagnosis. A standardized electro-clinical investigation specifying the topography, the evolution and the mechanism of the nerve damage enables the positive diagnosis of the neuropathy. Several elements orient the etiological diagnosis and allow to eliminate the main differential diagnosis: non systemic vasculitic neuropathy. The existence of associated systemic manifestations (glomerular or vascular nephropathy, interstitial lung disease, intra-alveolar hemorrhage, ENT involvement…), biological markers (ANCA, cryoglobulinemia, rheumatoid factor), and invasive examinations allowing histological analysis (neuromuscular biopsy) are all useful tools for.     

Retroperitoneal fibrosis associated with immunoglobulin G4-related disease

Retroperitoneal fibrosis is a rare disease characterized by the development of inflammation and fibrosis in the soft tissues of the retroperitoneum and other abdominal organs.Retroperitoneal fibrosis can be of 2 types:idiopathic and secondary.The recently advocated concept and diagnostic criteria of immunoglobulin G4(IgG4)-related disease,derived from research on autoimmune pancreatitis(AIP),has led to widespread recognition of retroperitoneal fibrosis as a condition caused by IgG4-related disease.We now know that previously diagnosed idiopathic retroperitoneal fibrosis includes IgG4-related disease;however,the actual prevalence is unclear.Conversely,some reports on AIP suggest that retroperitoneal fibrosis is concurrently found in about 10% of IgG4-related disease.Because retroperitoneal fibrosis has no specific symptoms,diagnosis is primarily based on diagnostic imaging(computed tomography and magnetic resonance imaging),which is also useful in evaluating the effect of therapy.Idiopathic retroperitoneal fibrosis can occur at different times with other lesions of IgG4-related disease including AIP.Thus,the IgG4 assay is recommended to diagnose idiopathic retroperitoneal fibrosis.High serum IgG4 levels should be treated and monitored as a symptom of IgG4-related disease.The first line of treatment for retroperitoneal fibrosis is steroid therapy regardless of its cause.For patients with concurrent AIP,i.e.,IgG4-related retroperitoneal fibrosis,the starting dose of steroid is usually 30-40 mg/d.The response to steroid therapy is generally favorable.In most cases,the pancreatic lesion and retroperitoneal fibrosis improve after the initial treatment.However,the epidemiology,treatment for recurring retroperitoneal fibrosis,and long-term prognosis are still largely unknown.Further analysis of such cases and research are necessary.     

Thoracic manifestations of IgG4-related disease

Immunoglobulin G4-related disease (IgG4-RD) is a recently described rare systemic fibroinflammatory disease with an estimated incidence of less than 1 in 100,000 persons per year. The disease can affect virtually any organ and is characterized by unifying histopathological findings. Recently, four subgroups of patients have been characterized: hepatobiliary, head and neck, Mikulicz syndrome and retroperitoneal fibrosis, who illustrate the mainly abdominal and ENT tropism of the disease. Yet, thoracic involvement is not uncommon. It can be detected in up to 30% of patients with systemic IgG4-RD and is the exclusive manifestation of the disease in about 10% of cases. Clinical symptoms are nonspecific and may include dyspnoea, cough or chest pain. Chest CT findings are heterogeneous and primarily include peribronchovascular thickening, nodules, ground-glass opacities and lymphadenopathy. There is no specific diagnostic test for IgG4-RD thoracic involvement, which may mimic malignancy or vasculitis. Therefore, a cautious approach is needed to make an accurate diagnosis: a search for extra-thoracic manifestations, elevated serum IgG4 levels, circulating levels of plasmablasts and pathologic evidence of disease is warranted. Although very suggestive, neither the presence of a polyclonal IgG4 lymphoplasmacytic infiltrate, storiform fibrosis or obliterative phlebitis are sufficient to confirm the histological diagnosis. Steroids are recommended as first-line therapy. Rituximab or disease-modifying antirheumatic drugs may be used in relapsed or rare cases of steroid-refractory disease. In this review, we summarize current knowledge regarding the pathophysiology, epidemiology, diagnostic modalities (clinical–biological–imaging–histopathology) and treatment of IgG4-RD thoracic involvement.     

Autoimmunity Related to IgM Monoclonal Gammopathy of Undetermined Significance

ABSTRACT In eight of 10 consecutive cases of IgM monoclonal gammopathy of undetermined significance (MGUS), the M-protein had specificity towards various tissues as estimated by direct and indirect immunofluorescence studies of skin and/or sural nerve biopsies. Five of the cases had neuropathy. In three of them, including two siblings with a demyelinating peripheral neuropathy, the IgM was bound to the myelin-associated glycoprotein (MAG) of peripheral nerves. One had axonal neuropathy with IgM activity against the peri- and endoneurium, while another case with post-infectious neuritis had IgM activity against structures in the endoneurium but no IgM autoimmunity in the direct fluorescence test. The latter improved clinically in parallel with a decrease in the M-protein indicating a pathogenetic role of the autoantibody. In three other cases, the IgM was bound to connective tissue structures, two of them also had plasma antibodies against the peri- and endoneurium in the indirect fluorescence test. Finally, two cases showed no reaction of the M-protein against any tissue structures. Since an autoimmune pathogenesis is suspected, the HLA types of seven patients are reported.     

Nonsystemic vasculitic neuropathy: a clinicopathological study of 22 cases

OBJECTIVE: The involvement of the peripheral nervous system in patients with systemic vasculitis has been reported, but nonsystemic peripheral nervous system vasculitis is not so well known. We investigated the clinical, electrophysiological, and pathological features of nonsystemic vasculitic neuropathy (NSVN) in order to establish the clinical and histological manifestations and to promote the earlier diagnosis of the syndrome. METHODS: Biopsies were selected from over 700 sural nerve biopsies performed at the Section of Neuropathology, Neurological Clinic of Athens University Hospital. The diagnosis of vasculitis was based on established clinicopathological criteria. Other causes of peripheral neuropathy were excluded. Complete laboratory, clinical, electrophysiological, and pathological studies were performed in all cases. RESULTS: Nerve biopsies of 22 patients were diagnosed as NSVN. The pathological features were vasculitis and predominant axonal degeneration with a varying pattern of myelinated fiber loss. The vasculitic changes were found mainly in small epineural blood vessels. Mononeuritis multiplex and distal symmetrical sensorimotor neuropathy were equally frequent. CONCLUSION: NSVN should be suspected in a case of unexplained polyneuropathy without evidence of systemic involvement. Clinical and neurophysiological studies are essential for the detection of nerve involvement, but the specific diagnosis of NSVN may be missed unless a biopsy is performed.     

Rethinking Ormond’s Disease: “Idiopathic” Retroperitoneal Fibrosis in the Era of IgG4-Related Disease

Idiopathic retroperitoneal fibrosis (RPF) is a periaortic sclerotic disease that encases adjacent retroperitoneal structures, particularly the ureters. A subset of idiopathic RPF cases can be associated with IgG4-related disease, but the frequency of this association is not clear. We selected 23 cases of idiopathic RPF and identified IgG4-related RPF cases based on the presence of IgG4+ plasma cells in the tissue, using an IgG4/IgG ratio cutoff of >40%. We then compared the IgG4-related RPF patients and the non-IgG4-related RPF patients in terms of both the presence of histopathologic features typical of IgG4-related disease and the simultaneous occurrence (or history) of other organ manifestations typical of IgG4-related disease. The IgG4-related RPF and non-IgG4-related RPF groups were also analyzed in terms of clinical, laboratory, and radiologic features and treatment review.We identified 13 cases of IgG4-related RPF (57% of the total cohort). The distinguishing features of IgG4-related RPF were histopathologic and extra-organ manifestations of IgG4-related disease. The IgG4-related RPF patients were statistically more likely than non-IgG4-related RPF patients to have retroperitoneal biopsies showing lymphoplasmacytic infiltrate (p = 0.006), storiform fibrosis (p = 0.006), or tissue eosinophilia (p = 0.0002). Demographics of the 2 groups, including a middle-aged, male predominance (mean age, 58 yr; 73% male), were similar.IgG4-related disease accounts for a substantial percentage of patients with “idiopathic” RPF. Histopathologic features such as storiform fibrosis, obliterative phlebitis, and tissue eosinophilia are critical to identifying this disease association. Extraretroperitoneal manifestations of IgG4-related disease are also often present among patients with IgG4-related RPF. Elevated IgG4/total IgG ratios in tissue biopsies are more useful than the number of IgG4+ plasma cells per high-power field in cases of RPF that are highly fibrotic.