April 2019 Case

Authors

Fellow: Kevin Ren, MD. Faculty: Mark Haas, MD PhD

Subject: Renal Pathology
Clinical History

A 30-year-old male with hepatitis C infection and history of intravenous (IV) drug abuse presents with altered mental status, nausea, vomiting, and night sweats. Review of systems is otherwise unremarkable, and he reports no recent travel. On physical examination, he appears cachectic and irritable. He is afebrile, normotensive, tachycardic, and maintains an oxygen saturation of 92% on room air. He has healed tracking marks in the antecubital fossa bilaterally. There is no splinter hemorrhage, Janeway lesions, Osler’s nodules, peripheral edema, or vasculitic rash.

Laboratory investigation shows marked leukocytosis (WBC 43 x 109/L), microcytic anemia (Hb 9.2 g/L, MCV 71), elevated serum creatinine (7.1 mg/dL), and hypoalbuminemia (2.9 g/dL). Urinalysis shows 2+ blood and 3+ protein. Urine protein creatinine ratio is 32 (approximately equivalent to proteinuria of 32 g/24hr). Urine toxicology is positive for amphetamines, cannabinoids, and opiates. Serologies for ANA and ANCA are negative. Complement levels are normal. SPEP and UPEP are negative for monoclonal proteins.

Renal ultrasound shows bilaterally enlarged kidneys with increased echogenicity, and doppler study shows decreased renal perfusion bilaterally without renal artery stenosis.

A renal biopsy is performed to investigate the cause of acute kidney injury and nephrotic range proteinuria.

Renal Biopsy
Light microscopy

Figure 1. Light microscopy shows normocellular glomeruli with their architecture obscured by an amorphous and acellular material expanding the mesangium and extending into the capillary walls. This material is eosinophilic on H&E stain, PAS weakly positive, sliver negative on Jones methenamine silver stain, and light blue on Masson’s trichrome stain. (400x magnification)

Congo red stain

Figure 2. The amorphous material is positive by Congo red stain and shows apple-green birefringence when viewed under polarized optics. (400x magnification)

Electron microscopy

Figure 3. (A) Electron microscopy shows fibrillary material expanding the mesangium and capillary walls. The fibrils segmentally extend into and expand the glomerular basement membranes [solid arrow]. There is extensive podocyte foot process effacement [hollow arrows]. (4800x magnification) (B) High magnification shows the fibrils measure between 7 to 12 nm in diameter. (25000x magnification)

Immunofluorescence

Figure 4. Immunofluorescence shows negative staining of the amyloid material by IgG, IgA, kappa, and lambda (appropriate internal positive control staining of podocyte protein resorption droplets [white arrows]) (400x magnification)

Figure 5. Immunohistochemistry shows strong staining of the amyloid material by serum amyloid A (SAA) in glomeruli, interstitium, and vascular walls. (200x magnification)

Diagnosis

Amyloid nephropathy, type AA (secondary amyloid), advanced with extensive glomerular involvement and focal arteriolar and interstitial involvement

Discussion

Amyloidosis represents a spectrum of diseases caused by deposition of misfolded proteins that form a beta-pleated sheet secondary structure. These misfolded proteins are Congo red positive and exhibit characteristic apple-green birefringence when viewed under polarized optics. Ultrastructurally amyloid proteins form linear, non-branching, randomly oriented fibrils that measures 7 to 12 nm in diameter when examined by electron microscopy (EM). The combination of positive Congo red staining and ultrastructural features of the amyloid fibrils can effectively distinguish renal amyloidosis from other renal diseases with organized deposits that often have a similar light microscopic appearance such as fibrillary glomerulonephritis, immunotactoid glomerulopathy, fibronectin glomerulopathy, and type III collagen glomerulopathy. (1, 2) The most recent amyloid nomenclature update published by the International Society of Amyloidosis in 2018 recognizes more than 36 different types of human amyloidogenic proteins with variable clinical presentation and organ involvement. (3)

The most common types of amyloid causing renal diseases include amyloid light-chain (AL), serum amyloid A (AA), leukocyte cell-derived chemotaxin 2 (ALECT2), and transthyretin (ATTR). The clinical features and distribution of different types of amyloid within the kidney (summarized in table 1) can be helpful in guiding the subsequent ancillary workup to subtype the amyloid protein.

Table 1. Characteristic clinical features and renal pathology findings of selected types of renal amyloidosis.
Table 1

The diagnosis of renal amyloidosis should be considered on renal biopsies when light microscopy shows glomerular, interstitial, or vascular infiltration by acellular, amorphous, eosinophilic material that is PAS weakly positive and silver negative. Glomeruli may show diffuse and/or nodular mesangial expansion by amyloid material that can also extend into glomerular capillary walls. Some cases can show silver positive spicules along capillary walls formed by bundles of amyloid fibrils oriented perpendicular to the glomerular basement membrane along the subepithelial surface. Congo red stain should be performed to demonstrate Congo red positivity and birefringence under polarized optics to confirm that the acellular, amorphous, and eosinophilic material represents amyloid. (4) Immunofluorescence (IF) staining for thioflavin T, though less commonly used than Congo red stain, can also be used to confirm the presence of amyloid. (5) EM is then required to definitively confirm the diagnosis of amyloidosis by demonstrating the characteristic linear, randomly oriented, non-branching fibrils measuring 7 to 12 nm in diameter, especially in light of recently reported cases of Congo red positive fibrillary glomerulonephritis. (1, 6)

The routine IF panel for medical renal biopsies (that includes IgG, IgA, IgM heavy chains, and kappa and lambda light chains) is useful in detecting AL, AH, or mixed AL and AH amyloidosis. If immunofluorescence is positive for light chain restriction and/or a monoclonal immunoglobulin heavy chain, appropriate confirmatory studies such as SPEP/UPEP or bone marrow biopsy should be considered if clinically appropriate to look for the source of monoclonal paraprotein production. If immunofluorescence is negative, immunohistochemistry (IHC) for SAA, transthyretin, and ALECT2 can be utilized to detect these subtypes. (4, 5)

Recently, laser microdissection mass spectrometry (LMD/MS) has emerged as an efficient and powerful tool to subtype amyloid, especially for the rare subtypes that do not have a readily available antibody for IF or IHC. LMD/MS uses a “shotgun” approach that does not require prior knowledge of the patient’s clinical information and can also help to solve cases with equivocal results from IF and IHC studies or when tissue is not available for IF or IHC studies. (1, 7)

Serum amyloid A (SAA) protein is an acute phase reactant that is produced in abnormally large quantities in chronic infections and inflammatory disorders. Accumulation of SAA protein cleaved by proteolytic enzymes can lead to AA amyloidosis. (8) Common etiologies of AA amyloidosis include chronic infections such as TB, osteomyelitis, and recurrent skin infections in IV drug users, as well as autoimmune diseases such as inflammatory bowel disease, ankylosing spondylitis, and rheumatoid arthritis. (5)

This patient has a history of IV drug use and hepatitis C infection, both of which are risk factors developing AA amyloidosis. The clinical presentation of nephrotic syndrome and extensive renal involvement by amyloid in glomerular, interstitial, and vascular compartments are also characteristic of AA renal amyloidosis. The treatment for AA amyloidosis hinges on controlling the underlying chronic infectious or inflammatory processes to decrease or stop the continuous production and accumulation of SAA. Patients can have stabilization or improvement of renal function and reduction in proteinuria if the underlying inflammatory disorder can be successfully treated. (9)

There are specific treatments for AA amyloidosis associated with certain underlying diseases. Colchicine can be used for AA amyloidosis associated with familial Mediterranean fever (FMF). (5)Inhibitory agents against proinflammatory cytokines including interleukin-1 beta (IL-1b), tumor necrosis factor-alpha (TNF-a), interleukin 6 (IL-6) have shown some benefit in AA amyloidosis caused by certain autoimmune inflammatory diseases. (9)

References
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