Paraproteins can manifest in many ways in the kidney. One that often brings confusion and can look very similar clinically and pathologically is AL amyloidosis and light chain deposition disease.
Beta pleated sheets
Usually fibrillary proteins( a diameter of 8 to 10 nm and may be up to 1 micrometer in length. They fibrils are randomly arranged and tend to form compact arrays when adjacent to cell membranes)
AL protein mainly lambda type usually seen with plasma cell dyscrasias
5% of the cases present with nephrotic syndrome
Usually older adults
An involve any organ, but the deposits with more clinical relevance are in kidneys, heart and liver. Other frequent locations are skin, tongue, peripheral nerves, gastrointestinal tract, and spleen.
Renal function effected only in 50% of the patients
In 2/3 of patients there is a monoclonal protein in urine. Bence Jones protein is usually not detected.
Glomeruli are affected in almost all the cases of AA amyloidosis and in less than half of AL amyloidosis. Deposits can be nodular or irregular in mesangium. Congo red positive
No cellular proliferation. In cases with little glomerular involvement diagnosis can be difficult and requires high suspicion to request Congo red and/or electron microscopy.
Amyloid is eosinophilic (pink) with H&E; weakly PAS-positive
Light Chain Deposition Diseases
It is an infrequent complication of myeloma
Kappa more than lamda( 4:1) ratio
Renal involvement is the one that dominates the clinical picture. can also see heart, liver, lungs, skin, and endocrine glands.
Non selective proteinuria usually as compared to AL amyloidosis
More chances to be seen with renal dysfunction, often associated with cast nephropathy if also present.
The most frequent finding in glomeruli is nodular glomerulopathy.
PAS-positive but do not stain with silver stains (unlike nodules in diabetic nephropathy) and they are Congo red and crystal-violet-negative (unlike those in amyloidosis).
The peritubular deposits are granular and very electron-dense. In glomeruli they are identified in the nodules, mesangium, and subendothelials. vascular disease can be seen as well.