RENAL PATHOLOGY LEARNING
Henoch-Schönlein nephritis
by
Franco Ferrario and Maria Pia Rastaldi
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Dr
Franco Ferrario Renal Immunopathology Center San Carlo Borromeo Hospital Milan, Italy |
Henoch-Schönlein syndrome, Schönlein-Henoch purpura, is recognized as a small vessel, multiorgan system vasculitis. The disease has been described worldwide. Signs and symptoms of the disease may include purpura, arthralgias, acute abdominal pain, and nephritis, in any combination. The variable pattern of organ involvement and the wide range of severity of the clinical and pathologic manifestations are considered to be consequences of variations in individual responses to differing loads of IgA-rich immune complexes. Among patients with Henoch-Schönlein syndrome, renal involvement is reported in 10% to 100%; a weighted mean of several series, encompassing approximately 2,000 patients, indicates that 40% of Henoch-Schönlein syndrome patients overall have nephritis.
| Henoch-Schönlein purpura nephritis |
| HSP nephritis is characterized, as in idiopathic IgAN, by mesangial damage with different degrees of hypercellularity with changes ranging from focal-segmental endocapillary proliferation to crescent formation. These lesions are extremely variable among patients and during the course of the disease in the single case. Different classifications consider the severity of the proliferative intra and extra-capillary lesions. Meadow et al considered the degree of mesangial proliferation, with endo-extra-capillary extension. Emancipator in 1992 revised Heaton's criteria in a more detailed classification. Six histologic classes are distinguished according to presence/absence and extension of extra-capillary proliferation, with subclasses defining the characteristics of the endo-capillary lesions. (Tab. 1) |
Table 1 – Classification of Henoch-Schönlein nephritis lesions according to Emancipator 1992
Class I |
Minimal glomerular lesions and absence of crescents |
Class II |
No Crescents IIa Pure mesangial proliferation IIb Focal-segmental endo-capillary proliferation IIc Diffuse endo-capillary proliferation |
Class III |
Presence of extra-capillary cellular proliferation in less than 50% of glomeruli IIIa In association with focal and segmental endo-capillary proliferation IIIb With diffuse endo-capillary proliferation |
Class IV |
Florid extra-capillary cellular proliferation in 50-75% of glomeruli IVa In association with focal and segmental endo-capillary proliferation IVb With diffuse endo-capillary proliferation |
Class V |
Extra-capillary proliferation in more than 75% of glomeruli Va In association with focal and segmental endo-capillary proliferation Vb With diffuse endo-capillary proliferation |
Class VI |
Pseudo-membranoproliferative glomerulonephritis |
Glomeruli can be completely normal or show only minimal lesions.
More commonly, a focal and segmental mesangial proliferation can be seen.
In other cases, mesangial proliferation can be more severe and diffuse. All these patterns are shared by idiopathic IgA GN.
Segmental endocapillary proliferation may accompany mesangial proliferation.
Much more severe endocapillary proliferation and exudation can be observed. Differential diagnosis has to be made from acute post-streptococcal GN, through immunofluorescence demonstration of IgA deposition.
Necrotizing-extracapillary glomerulonephritis frequently involves less than 50% of glomeruli. In the remaining part of the tuft, endocapillary proliferation and exudative lesions may be present.
Necrotizing-extracapillary lesions may involve more than 50% of glomeruli. In these patients a rapidly progressive glomerulonephritis is frequently observed.
In rare cases circumferential cellular crescents can be present in 80-100% of glomeruli. In these cases there is a marked compression of the tuft.
Monocyte-macrophages are detected by immunohistochemistry in necrotizing-extracapillary lesions. This aspect is similar to that observed in other forms of necrotizing nephritis (ANCA-associated vasculitis, anti-GMB antibody disease, IgA GN).
In the same way, monocyte recruitment appears to be mainly mediated by VCAM-1 adhesion molecule.
In rare cases the histological pattern is characterized by a membranoproliferative glomerulonephritis, with massive mesangial proliferation and basement membrane thickening with double contours, undistinguishable, if not by immunofluorescence, from idiopathic MPGN.
In many cases more chronic lesions are present, characterized by well delineated segmental areas of glomerulosclerosis with capsular adhesion and these can represent reparative stages of the necrotizing extracapillary damage.
Independently of glomerular damage, interstitial leukocytes can be present.
Monocyte-macrophages (CD68) and T-lymphocytes (CD3) are generally observed in the interstitium. Arterial hyalinosis can be seen especially in adults.
Glomerular IgA deposition is diagnostic. As in Berger's disease, the most common pattern is represented by mesangial deposition, but several other patterns can be observed.
By electron microscopy, as in idiopathic IgA GN, mesangial proliferation and mesangial electrondense deposits are commonly detected. Endothelial hypertrophy is not rarely seen. (x 2800)
The cohort of patients gathered by the Italian collaborative study showed a few cases with important extra-capillary proliferation (Classes IV and V in Table 1). More than 50% of the biopsies of both adults and children did not have proliferative extra-capillary lesions (Classes I and II).
When present, these lesions involved less than 50% of glomeruli (Class III).
