Figure 1143

Biopsy specimen of immunotactoid glomeru-lonephritis with immunoglobulin A-X deposits. The patient had no signs of a monoclonal gammopathy or lymphoma. A, Mild increase of mesangial matrix with segmental irregularity of the capillary wall. B, Immunofluorescence. The deposits are positive for X (and immunoglobulin A) C, Below the glomerular basement membrane, seen is an accumulation of short microtubules with a diameter of about 30 nm. (Part A, methenamine silver. Original magnification X400, X400, X25,000, respectively.)

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FIGURE 11-43 (Continued)

Immunotactoid and fibrillary glomerulonephritis are comprised of lesions characterized by the deposition of immunoglobulins (and complement) arranged in randomly distributed fibrils or microtubules in the capillary wall and mesangium [89,90]. These lesions are thicker than are amyloid fibrils and are negative on congo-red staining. Although presently it is not clear whether these forms of glomerulonephritis are different disease entities or are different morphologic expressions of one disease, some morphologic and clinical features exist that suggest fibrillary glomerulonephritis must be distinguished from immunotactoid glomerulonephritis [91]. Immunotactoid glomerulonephritis shows deposition of microtubules with diameters of 35 to 50 nm and commonly is associated with a lymphoprolifera-tive disease. The deposited immunoglobulins frequently are of monoclonal composition. In contrast, fibrillary glomerulonephritis is characterized by fibrils with diameters of about 18 to 20 nm. The deposited immunoglobulins usually are polyclonal and very rarely monoclonal. An association with a lymphoproliferative disease is uncommon in contrast to immunotactoid glomerulonephritis.

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