—  SPECIALTY CONFERENCE  —

Renal Pathology

Case 2 - PR3-ANCA Associated Systemic Small Vessel Vasculitis with Involvement of Dermal Vessels and Vasa Recta of the Renal Medulla

Isaac E. Stillman
Beth Israel Deaconess Hospital
Boston, MA





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Clinical History
63 year-old man presented to an outside hospital with malaise. He reported taking Aleve 800 mg q6 for the past 4-5 weeks as well as ibuprofen 800 mg daily PRN for muscle pain. Stated that his urine was occasionally pink-red over the past 2 weeks. He was found to be oliguric, with a SCr of 6, and a BUN of 58. UA showed pyuria, large blood and large protein. Renal ultrasound revealed a right staghorn calculus with moderate hydronephrosis. Ureteral stent was placed for presumed obstruction. Follow-up ultrasound showed improvement in the hydronephrosis, but the serum creatinine remained unchanged. Hyperkalemia developed, and hemodialysis was initiated. Transferred to BIDMC for further evaluation. Past Medical History: Obesity and hypertension. Bilateral nephrolithiasis (staghorn calculus on right, non- obstructing stones on left) Chronic kidney disease ( baseline Serum creatinine 1.6 - 1.8 (eGFR 41 ml/min).

Pertinent Laboratory Data:

CBC: WBC 8.4, Hgb 9.6, Hct 29.1, Plt 217

Chemistries: Na 136, K 4.9, Cl 99, HCO3 35, Creatinine 5.7, BUN 61 Glucose 103, Ca 8.6, Mg 2.3, PO4 6.1 RF 30 CRP 115.8 Hepatitis B & C Negative ANA and dsDNA Negative Complements Within normal limits Pr / Cr = 4.2 Dipstick 3+ protein, 3+ blood, 1-2+ esterase, pH 6.0

Microscopy: Numerous RBCs, WBCs, few granular and RBC casts, positive for dysmorphic RBCs and eosinophils


Case 2 - Figure 1
Tubulointerstitium with widespread but patchy edema, mononuclear inflammation (eosinophils present), and tubulitis. Fibrosis and atrophy is present but not advanced.
Case 2 - Figure 2
Only intact glomerulus, at the tissue edge with crush artifact, is otherwise normal.
Case 2 - Figure 3
Vasa recta (likely ascending) showing endothelial activation and fibrinoid necrosis.
Case 2 - Figure 4
Fibrinand hemorrhage tracking along intact vasa recta.

Case 2 - Figure 5
Frozen remnant (from IF) contained 3 glomeruli, all unremarkable.
Case 2 - Figure 6
Glomerulus showing segmental immunodeposition.
Case 2 - Figure 7
Focal Bowman's capsule rupture with associated cells within urinary space and interstitium.
Case 2 - Figure 8
Intact glomerulus without necrosis or capillary wall deposits.

Case 2 - Figure 9
Mesangial matrix with occasional paramesangial/mesangial granular electron dense deposits.
Case 2 - Figure 10
Skin biopsy, foot, showing vasculitis involving small to medium sized vessels throughout the full thickness of the dermis.
Case 2 - Figure 11
Deep vein, adjacent to subcutaneous fat, with predominantly neutrophilic vasculitis.
Case 2 - Figure 12
Arteriole at base of biopsy with focal fibrinoid necrosis.

Introduction:
This renal biopsy represents an atypical presentation of a relatively common diagnosis. That entity, usually recognized on the basis of cortical (glomerular) lesions, was diagnosed here on the basis of medullary findings, and confirmed by other studies. This case also serves as an opportunity to review the unique microenvironment of the renal medulla, and its possible relationship to the pathogenesis of this disease.

Pathological/Microscopic Findings and any Immunohistochemical or Other Studies:
Specimen: Needle biopsy of kidney. Light Microscopy:The specimen predominantlyconsisted of renal medulla. Some deep renal cortex was present; it contained two glomeruli, one of which wasglobally sclerotic. The other, a partial tuft, was located at the tissue edge and showed some crush artifact, but was otherwise within normal limits. Given the limited cortical sampling, the frozen remnant (from the immunofluorescence preparations) was reviewed and found to contain three unremarkable glomeruli. Specifically, they did not show any necrosis or crescent formation. The cortex showed widespread but patchy edema and mononuclear inflammation (eosinophils present) with tubulitis. These acute changes made it somewhat difficultto gauge the extent of the interstitial fibrosis and tubular atrophy, but it was not felt to be advanced. No neutrophilic capillaritis or granulomatous inflammation was noted. Cortical arteries showed mild intimal fibroplasia. Arterioles showed mild mural thickening, with some hyalinechange. No cortical vasculitis was noted. The medullary interstitium also showed patchy edema and mononuclear inflammation. Several medullary vessels (vasa recta) showed fibrinoid necrosis, with associated endothelial changes of activation and detachment. Immunofluorescence:The specimen consisted of renal cortex and medulla. The IgG preparations contained 3 glomeruli (all intact), one of which showed a very small focus of segmental positivity (the remaining two were entirely negative). All other preparations showed no glomeruli. No extra-glomerular staining was seen for IgA, IgM, Kappa, Lambda, and C1q. 1+ C3 was present along tubular basement membranes and in vessels. No vascular or tubulointerstitial staining was noted on fibrin. Albumin was non-contributory. Electron microscopy: Fine structural studies of a single representative glomerulus revealed a focus of Bowman's capsule rupture with associated cells (some clearly inflammatory)withinboth the urinary space and the interstitium.There was irregular foot process effacement. No definite areas of necrosis were identified. Overall basement membrane thickness was within normal limits; areas of ischemic type change with wrinkling were noted. No subepithelial or subendothelial granular electron dense deposits were seen. The mesangial matrix wassomewhat increased and occasional paramesangialand mesangial granular electron dense deposits were seen.

On hospital day 5 the patient was noted to have developed a non-blanching confluent macular rash with poorly defined borders on his left foot, with similar but smaller areas on both upper and lower extremities, thought to be characteristic for leukocytoclastic vasculitis. A punch biopsy of skin showed a vasculitic process involving small to medium sized vessels through the full thickness of the dermis. Some deep small vessels in the subcutaneous fat at the biopsy base were also involved, although to a lesser extent. There was marked fibrin extravasation and the associated inflammatory infiltrate was predominantly neutrophilic, with some admixed eosinophils. The inflammatory infiltrate was predominantly vascularand perivascular in distribution. No granulomatous inflammation wasseen.

At that time, the results of additional blood tests became available. The patient was found to be positive for c-ANCA (1:640) with antibodies to proteinase 3 (3,789 units of antibody activity by sandwich ELISA, with >20 = positive). ELISA for anti-myeloperoxidase and serum anti-GBM were negative.

Differential Diagnoses:
  • ANCA Associated Systemic Vasculitis (AAV)

  • Microscopic polyangiitis (MPA)

  • Wegener's granulomatosis (WG)

  • Acute Interstitial Nephritis (AIN)

Final Diagnosis:
PR3-ANCA Associated Systemic Small Vessel Vasculitis with Involvement of Dermal Vessels and Vasa Recta of the Renal Medulla.

Case Discussion:
This patient shows evidence of a systemic c-ANCA positive vasculitis involving skin and kidney, without respiratory tract involvement. ANCA are associated with many cases of WG, MPA, Churg-Strauss syndrome, "renal-limited" vasculitis, and some drug-induced vasculitides. This patient lacked the signs of Churg-Strauss (rhinitis, asthma, and blood eosinophilia), had no drug history, and had dermal involvement, excluding renal limited disease. His PR3 (proteinase 3) -ANCA positivity favors WG over MPA (typically MPO (myeloperoxidase)-ANCA). However, there is enough overlap between the two ANCAs that in an individual these diseases cannot be distinguished on the basis of serology. The major clinical reason to make the distinction is that WG may be more likely than MPA to relapse. However there is controversy as to the definition of these two entities, and some evidence suggests that they are likely related conditions. The Chapel Hill Consensus Conference defines MPA as a small vessel vasculitis that lacks the defining features of WG (typically upper respiratory tract destruction or lesions in the lower respiratory tract with granulomatous inflammation). The lack of these findings in our patient would favor MPA. However, many well established cases of WG do not show granulomas, perhaps due to sampling in some. This patient highlights the potential difficulty in establishing a specific diagnosis. Indeed, there is a recent trend to avoid these definitional problems by using the terms proteinase 3, myeloperoxidase, or seronegative ANCA disease. This is supported by the likelihood that the ANCA subtype may have more therapeutic and prognostic significance than the terms MPA or WG.

The classic finding on renal biopsy in the setting of AAV is a pauci-immune segmentally necrotizing / crescentic glomerulonephritis. Rupture of Bowman's capsule, seen here, may be associated with more intense interstitial inflammation. Granulomatous inflammation in continuity with such a lesion does not necessarily suggest WG. Fibrinoid necrosis of cortical vessels is seen in about 15% of cases, and does not appear to have a specific prognostic significance. Cortical tubulo-interstitial inflammation, primarily mononuclear, may be prominent, and even suggest AIN. Indeed there are case reports of AAV presenting pathologically as AIN, with a crescentic glomerulonephritis seen only on follow-up biopsies. On the other hand, occasional cases of drug induced AIN may be associated with ANCA positivity, in the absence of AAV.

The modifier "pauci-" is indicated as many cases do not show entirely negative glomeruli by immunofluorescence. Haas et al in a study of 126 cases of ANCA associated crescentic GN found that 54% of them showed immune complex deposits on EM. Of those, 87% also showed IF findings for at least one Ig or complement component; staining was relatively mild in most (2+ or less). Nearly half of the biopsies negative by EM also showed positive IF; the intensity of staining in those was typically very weak. The presence of deposits on EM was found to be associated with higher levels of proteinuria and a greater percentage of glomeruli with crescents.

AAV findings in the renal medulla have been overlooked by many descriptive, prognostic, and nosologic studies. For example, the recently published Histopathologic classification of ANCA-associated glomerulonephritis is entirely glomerulocentric. This is due, in part, to the inconstant presence of medullary tissue. Nevertheless, some studies do address the medulla. Interestingly, one of the early descriptions of ANCA disease, Jennette et al. in 1989, noted a medullary peritubular necrotizing leukocytoclastic capillaritis in 3 of 89 cases. They noted that the frequency of this lesion's occurrence cannot be determined because of its focality and the lack of medulla in many biopsies. Bonsib et al., 1994, published the best series study of the medulla in this setting. 105 renal biopsies from patients with ANCA and anti-GBM antibody-associated diseases were reviewed for medullary lesions. Necrotizing medullary lesions were identified in eight of 56 cases in which medullary tissue was present. All eight were in patients with AAV (7, C-ANCA; 1 P-ANCA). Four types of medullary lesions were identified; leukocytoclastic capillaritis (7 cases), necrotizing arteriolitis (2 cases), pathergic granulomas (3 cases) and papillary tip necrosis (1 case). Notably, both medullary lesions (arteriolitis and peritubular capillaritis) developed without corresponding cortical lesions (arteriolitis or peritubular capillaritis. Although necrotizing glomerulonephritis was present in seven of eight patients, its activity did not parallel the severity of the medullary lesions. They concluded that several forms of necrotizing medullary vascular lesions may develop in ANCA-associated disease and that there is discordance between cortex and medulla regarding degree of activity and types of vessels affected. A case report of WG initially presenting as acute suppurative interstitial nephritis by Banerjee et al noted that the inflammation was present as streaks through the medulla only. They speculated that this pattern may represent "an early event in the natural history" of the vasculitis. These and other studies suggest that the medullary expression of AAV may have different nuances than that seen in the extra-glomerular cortex. Could this be explained by differences between cortical and medullary environments? The most likely factor is medullary hypoxia. An additional consequence of the counter-current system is tissue hypertonicity. Some studies suggest a medullary environment that is "hostile to inflammation". Finally, low blood flow, diminished shear stress and regional endothelial phenotypes also contribute to the unique medullary microenvironment.

The pathogenesis of AAV is complex and incompletely understood, and further complicated by the occurrence of ANCA negative vasculitis. Nonetheless, there is increasing evidence supporting a pathogenetic role for ANCA and the importance of neutrophil activation. In recent years increasing attention has been given to the role of endothelial activation, a welcome development, given that the disease under study is vasculitis. Generally speaking, activated endothelium is prothrombotic, proadhesive, leaky, and vasoconstricted. Activation in medullary vessels would likely exacerbate baseline hypoxia. In AAV, activated neutrophils likely activate the endothelium, with associated upregulation of adhesion molecules and chemoattractant release, a process potentiated by cytokines such as IL-8. TNF-α plays a central part in this process as it activates both neutrophils and endothelial cells. The morphologic lesions of endothelial activation - swelling, necrosis, and detachment, seen in the medulla of this case, may be preceded by loss of CD34 positivity and have their systemic equivalent in the circulating endothelial cells and microparticles whose blood levels have been found to correlate with AAV disease activity. Angiogenic factors, such as VEGF, undoubtedly play a role in this process. Angiopoietins, the second family in this group, are gaining increasing attention as regulators of endothelial activation, with relevance to medullary vessels. Their common receptor, Tie-2 is almost exclusively expressed by endothelial cells and immunoperoxidase studies of mature mice localize it to post-glomerular capillaries including the vasa recta. Its two best studied ligands, Angiopoietin 1 and 2 are antagonizing, with Ang-1 promoting vessel integrity, inhibiting vascular leakage and inflammatory gene expression. In contrast, Ang-2 (stored in Weibel-Palade bodies and thus may act in a paracrine/autocrine manner) binding abrogates protective Ang-1/Tie2 signaling, increases inflammation, and promotes endothelial detachment. Studies of Ang2–/– mice document their impaired ability to initiate a neutrophilic response. Cellular experiments show that Ang-2 promotes adhesion by sensitizing endothelial cells toward TNF-α and modulating TNF-α –induced expression of endothelial cell adhesion molecules. Ang-2/LacZ expression in heterozygous postnatal mice primarily localizes to the outer medulla. Evidence for the relevance of Ang-2 in AAV includes studies showing Ang-2 over-expression (in podocytes) causes glomerular endothelial apoptosis and that systemic Ang-2 administration induces capillary leakage. Circulating Ang-2 is elevated in AAV and closely correlates with clinical scores of disease activity and numbers of circulating endothelial cells. Medullary associated findings include the critical role of Ang-2 in the development of post-glomerular vasculature and that in-vivo Ang2 levels are higher in veins than arteries, perhaps related to the finding that hypoxia upregulates expression of both Ang-2 and the Tie2 gene. Furthermore, low flow increases Ang2 expression (possibly facilitated by VEGF) and long-term low laminar shear stress induces Ang-2 expression and release, while high stress does the opposite. Much of this data is preliminary and fragmentary. Nevertheless, recent advances in our understanding of endothelial activation have begun to shed new light on AAV and the renal medulla.

Review of Treatment Options:
Prompt recognition and treatment is necessary. Cyclophosphamide and glucocorticoids induce remission in most. In those with severe disease, plasmapheresis may improve renal function and reduce the risk of progression to end-stage renal disease. Although experience is still limited, Rituximab may be as effective as cyclophosphamide in patients with severe disease.

Conclusions:
  • ANCA associated pauci-immune crescentic glomerulonephritis is not just a glomerular disease!

  • Medullary expressions of "cortical" processes may be related to its specific microenvironment

  • Examination of the medulla is not just a "cortical substitute", and may also lead to insights into pathogenesis


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