Usually when we think of amyloidosis in the kidney- we think of paraprotein mediated amyloidosis (AL or AH) leading to nephrotic syndrome and in some rare cases- vascular amyloid presenting as AKI.
A recent study published in Mayo Clinic Proceedings suggests that renal infarction might be a common finding in patients with cardiac amyloidosis. Three groups of patients were identified according to the underlying amyloidosis disorder: AL amyloidosis in 24 patients, mutated-transthyretin amyloidosis in 24 patients, and wild-type transthyretin amyloidosis in 39 patients. Patients with AL amyloidosis had significantly higher N-terminal pro-B-type natriuretic peptide levels (P=.02) and were more likely to have nephrotic syndrome (P<.001). Renal infarction was detected in 18 patients (20.7%), at similar frequencies in the various groups. The likelihood of RI diagnosis was 47.1% (8 of 17) in the presence of AKI and 14.5% (10 of 69) in its absence (P=.003). Renal infarction (defined by defect(s) on the DSMA scan) was reported in 20.7% of patients with and 25% without evidence of cardiac amyloidosis. Prior studies have not really shown any association like this before of amyloidosis and infarction. Renal infarcts were described in an autopsy study in 3 kidneys that had either cast nephropathy, plasma cell nodules, or autolysis but not with amyloid deposits. Dang et al interesting are reporting is a high percentage of abnormal DSMA scans in patients with wild-type transthyretin amyloidosis (wtATTR) and mutant transthyretin amyloidosis (mATTR) amyloidosis.
These findings are intriguing. The 20% to 25% prevalence reported by Dang and colleagues was therefore unexpected. Renal involvement in ATTR is thought to be rare, especially in patients with wtATTR amyloidosis. Recent drugs used to treat this form of amyloidosis might lead to a glomerulonephritis( my recent post). The finding from the current study suggests that we may be vastly underestimating the prevalence of kidney involvement in ATTR amyloidosis. These patients usually don’t present with nephrotic range proteinuria but more with AKI and subacute AKI. Perhaps, instead of labeling all of these as cardio-renal syndrome, we should consider looking for renal infarction in these patients. And as I have always thought about ruling out amyloidosis in young males who present with renal infarction, I usually stop at AL-AH amyloidosis testing. Given the above findings, perhaps an amyloid scan to look for wtATTR and mATTR might be important as perhaps renal infarction could be a potential relationship here.
Quite an interesting association!!