Renal Biopsy

Brian McNally, M.D.

Specimen Type:

Kidney

History:

A 34 year old female without a significant past medical history presented with microhematuria. Dipstick urinalysis was negative for protein. Her serum creatinine was within normal limits. The serologic workup was negative.

Pathologic Features:

Light Microscopy

Sections of the tissue submitted for light microscopic examination consist of renal cortex. The sections contain up to six (6) glomeruli. All glomeruli are viable (figures 1 and 2). Neither segmental nor global tuft sclerosis is present. The capillary loop walls are unremarkable, and the capillary loops are patent. There is no crescent formation. The tubules are unremarkable, and have distinct brush borders (figure 3). There is no interstitial fibrosis, tubular atrophy, or inflammation. The vessels are unremarkable. There is no vascular sclerosis or thickening. Neither vasculitis nor thrombosis is present. A Congo red stained section is negative for amyloid.

Immunofluorescence

Sections of the tissue submitted for immunofluorescence microscopic examination contain up to seven (7) glomeruli. All tufts are viable. Findings are as follows:

  • Albumin: Diffuse, basement membrane and matrix, linear, 1+.
  • IgG: Negative.
  • IgM: Diffuse, matrix, granular, 1+ (figure 4).
  • IgA: Negative.
  • C1q: Negative.
  • C3: Focal arteriolar, Bowman's capsule, interstitial, 1+.
  • Fibrinogen: Diffuse, tubulointerstitial, weak.
  • Kappa: Negative.
  • Lambda: Negative.
  • Type IV collagen alpha1 chains: Diffuse, glomerular basement membrane/Bowman capsule, linear, 3+. Focal/continuous, tubular basement membrane, linear, 3+.
  • Type IV collagen alpha3 chains: Diffuse, glomerular basement membrane/Bowman capsule, linear, 3+. Focal/continuous, tubular basement membrane, linear, 3+.
  • Type IV collagen alpha5 chains: Diffuse, glomerular basement membrane/Bowman capsule, linear, 3+. Focal/continuous, tubular basement membrane, linear, 3+.
Electron Microscopy

Sections of the tissue submitted for electron microscopic examination contain up to three (3) glomeruli. The glomerular basement membranes (GBM's) are variably thinned (figure 5). Most GBM's measure between 200 and 230 nm thick. The mesangial matrix is not expanded. There are no subendothelial, subepithelial, or mesangial/paramesangial electron-dense, immune complex-type deposits. The podocyte foot processes are unremarkable.

Differential Diagnosis:

Not applicable for this case, please continue to the Diagnosis.

Diagnosis:

Kidney, biopsy—Thin basement membrane nephropathy (TBMN)

TBMN is a pathologic finding observed in some patients with hematuria, and it is characterized at the ultrastructural level by attenuation of the GBM (3). Although the attenuation is usually diffuse, it may be segmental. This entity is the most common cause of persistent glomerular bleeding in children and adults. Most affected individuals have, in addition to the hematuria, minimal proteinuria, normal renal function, and a family history of hematuria. The clinical course is usually benign (1). The differential diagnosis includes Alport Syndrome (AS) variants, because kidney biopsy specimens from patients with one of these variants can also contain thin GBM’s.

The incidence of TBMN in patients with hematuria is difficult to ascertain, because its demonstration is dependant on multiple factors. These factors include, but are not limited to the indication for renal biopsy, the availability of electron microscopy, and the definition of an abnormally thin GBM. Electron microscopic examination must be performed in order to make this diagnosis. Presently, there is disagreement about the upper and lower limits of normal adult GBM thickness. Although one study concluded that a normal adult GBM measures 350 +/- 43 nm wide, other studies have established different ranges (3). Despite these limitations, the generally accepted incidence of TBMN is estimated to be between 1% and 2%. In some patients, TBMN coexists with other abnormalities. The diseases most often associated with incidental TBMN are focal segmental glomerulosclerosis and minimal-change disease (2).

On light microscopic examination, kidney biopsy specimens from patients with TBMN usually appear normal (3). Focal-global glomerulosclerosis is rarely noted (4).

Immunofluorescence for type IV collagen alpha3 chains and type IV collagen alpha5 chains is positive in kidney biopsy specimens from patients with TBMN. The staining is generally present in the GBM’s, Bowman capsules, and distal tubular basement membranes. This pattern of staining is important, because it helps distinguish between TBMN and AS variants. Further, immunofluorescence studies can be helpful in establishing the mode of inheritance of AS. The GBM’s, Bowman capsules, and distal tubular basement membranes of males with X-linked AS generally do not express type IV collagen alpha3 chains and type IV collagen alpha5 chains. Discontinuous staining in these compartments is indicative of an X-linked carrier (heterozygote). In the autosomal recessive form of AS, Bowman capsules and distal tubular basement membranes express type IV collagen alpha5 chains (the GBM’s are negative). The GBM’s, Bowman capsules, and distal tubular basement membranes generally do not express type IV collagen alpha3 chains in the autosomal recessive form of AS (5). Conventional immunofluorescence is usually negative in kidney biopsy specimens from patients with TBMN (3).

Although the kidney biopsy specimens from patients with TBMN usually display diffuse GBM attenuation, the attenuation is segmental in a considerable number of patients. In light of this observation, some investigators suggest that TBMN should be defined as a clinicopathologic entity of dysmorphic hematuria and a diffusely or segmentally thinned GBM (4) Other problems with the definition of TBMN exist. For example, there are no standardized diagnostic criteria defining the degree or extent of GBM thinning required for the diagnosis of TBMN. GBM thinning is often seen in other glomerulopathies, where it may represent an overlap with TBMN, or may be secondary to GBM damage and remodeling. Importantly, TBMN must be differentiated from the GBM thinning seen in some renal biopsy specimens from boys and female heterozygotes with X-linked AS, because these two conditions have very different prognoses (6).

The urine of most patients with TBMN contains blood. Other abnormalities in the urinalysis may be present, as some patients carry a dual diagnosis of focal segmental glomerulosclerosis (FSGS) and TBMN. In one study, these patients presented with microscopic hematuria, mild proteinuria, and variable degrees of renal impairment. This study also concluded that certain mutations in the COL4A3/COL4A4 genes of type IV collagen either predispose some patients to FSGS and chronic renal failure, or that TBMN sometimes coexists with another genetic modifier that is responsible for FSGS and progressive renal failure (7). Microscopic hematuria, usually detected in childhood by routine urinalysis, is the classic clinical finding in patients with TBMN (3).

In 1996, Lemmink et al established for the first time that benign familial hematuria (BFH) with thin GBM may be due to type IV collagen mutations: they identified a heterozygous mutation in COL4A4 segregating with the disease in a family affected with autosomal recessive AS and BFH (3). More recent studies have determined that many cases of TBMN are familial and show autosomal-dominant inheritance. It is unclear whether individuals with TBMN and impaired renal function represent part of the spectrum of TBMN associated with heterozygous COL4A3 or COL4A4 mutations; or, if their disease is caused by mutations of other genes; or, whether it is caused by a second coexistent renal lesion; or, is misdiagnosed Alport syndrome (8).

Another study revealed that 40% of families with TBMN have hematuria that segregates with the corresponding locus (COL4A3/COL4A4), and identical mutations occur in both TBMN and autosomal-recessive AS. Approximately 20 COL4A3 and COL4A4 mutations have been identified in TBMN, and these mainly are single nucleotide substitutions that are different in each family. The families in whom hematuria does not appear to segregate with the COL4A3/COL4A4 locus cannot all be explained by de novo mutations, and nonpenetrant or coincidental hematuria (9). Whereas heterozygous COL4A3 and COL4A4 mutations are clearly involved in some cases of BFH, genetic heterogeneity is suggested by at least two reports (3).

This discussion has mainly addressed TBMN and AS, but other inherited diseases of the GBM are worth mentioning. Patients with hematuria, thin GBM’s, normal-appearing glomeruli by light microscopy, and no significant immune deposits may or may not have BFH (3). Like all basement membranes, the GBM contains different isoforms of type IV collagen, laminin, nidogen, and heparin sulfate proteoglycans. These isoforms have a tissue-specific distribution; in the mature GBM, the major type IV collagen molecule is the alpha 3 alpha 4 alpha 5(IV) isoform, associated with laminin-521 (alpha 5 beta2 gamma 1), nidogen and agrin heparan sulfate proteoglycans. The importance of the GBM has been demonstrated by identification of hereditary glomerular diseases linked to structural anomalies of its components; for example, laminin in Pierson syndrome. Type III collagen, an interstitial collagen, accumulates in the GBM of patients with the nail-patella syndrome. Abnormal deposition of fibronectin, another extracellular matrix protein, is characteristic of so-called fibronectin nephropathy (10).

References:

  1. Savige J, Rana K, Tonna S, Buzza M, Dagher H, Wang YY. Thin basement membrane nephropathy. Kidney Int. 2003 Oct; 64(4):1169-78.
  2. Haas M. Thin glomerular basement membrane nephropathy: incidence in 3471 consecutive renal biopsies examined by electron microscopy. Arch Pathol Lab Med. 2006 May; 130(5):699-706.
  3. Heptinstall’s pathology of the kidney.—6th ed./editors, J. Charles Jennette… [et al.].
  4. Ivanyi B, Pap R, Ondrik Z. Thin basement membrane nephropathy: diffuse and segmental types. Arch Pathol Lab Med. 2006 Oct; 130(10):1533-7.
  5. Haas M. Alport syndrome and thin glomerular basement membrane nephropathy: a practical approach to diagnosis. Arch Pathol Lab Med. 2009 Feb; 133(2):224-32.
  6. Foster K, Markowitz GS, D'Agati VD. Pathology of thin basement membrane nephropathy. Semin Nephrol. 2005 May; 25(3):149-58.
  7. Voskarides K, Damianou L, Neocleous V, Zouvani I, Christodoulidou S, Hadjiconstantinou V, Ioannou K, Athanasiou Y, Patsias C, Alexopoulos E, Pierides A, Kyriacou K, Deltas C. COL4A3/COL4A4 mutations producing focal segmental glomerulosclerosis and renal failure in thin basement membrane nephropathy. J Am Soc Nephrol. 2007 Nov; 18(11):3004-16. Epub 2007 Oct 17.
  8. Gregory MC. The clinical features of thin basement membrane nephropathy. Semin Nephrol. 2005 May; 25(3):140-5.
  9. Rana K, Wang YY, Buzza M, Tonna S, Zhang KW, Lin T, Sin L, Padavarat S, Savige J. The genetics of thin basement membrane nephropathy. Semin Nephrol. 2005 May; 25(3):163-70.
  10. Gubler MC. Inherited diseases of the glomerular basement membrane. Nat Clin Pract Nephrol. 2008 Jan; 4(1):24-37.