Mass spectrometry analysis reveals non-mutated apolipoprotein A1 lumbosacral radiculoplexus amyloidoma.
BACKGROUND
In rare instances, amyloidosis presents as a focal, macroscopic lesion involving peripheral neural tissues (amyloidoma). In all known reported cases, peripheral nerve amyloidomas have had immunoglobulin light-chain fibril composition and occurred in the context of paraproteinemia.


METHODS
A 46-year-old man presented with progressive insidious-onset right lumbosacral radiculoplexus neuropathy without paraproteinemia. MRI-targeted fascicular nerve biopsy was performed on an enlarged sciatic nerve after earlier distal fibular nerve biopsy was nondiagnostic. Laser dissected mass spectroscopy of the discovered amyloid protein was performed after immunohistochemistry failed to identify the specific amyloid protein. Complete gene sequencing of apolipoprotein A1 (ApoA1) was performed.


RESULTS
Only wild-type ApoA1 amyloid was found in the congophilic component in the nerve.


CONCLUSIONS
This case highlights the utility of MRI-guided fascicular nerve biopsy combined with laser-dissected mass spectrometric analysis. Importantly, the case expands the known causes of amyloidomas to include wild-type ApoA1.
Department of Neurology, Mayo Clinic, 200 First Street SW, Rochester, Minnesota 55905, USA.
Adam J
AJ
Loavenbruck
Vinay
V
Chaudhry
Steven R
SR
Zeldenrust
Robert J
RJ
Spinner
Jason D
JD
Theis
Christopher J
CJ
Klein
D000595:Amino Acid Sequence; D000686:Amyloidosis / Q000175:diagnosis* / Q000235:genetics / Q000473:pathology; D016632:Apolipoprotein A-I / Q000235:genetics*; D006801:Humans; D008160:Lumbosacral Plexus / Q000473:pathology*; D008297:Male; D013058:Mass Spectrometry; D008875:Middle Aged; D008969:Molecular Sequence Data; D010523:Peripheral Nervous System Diseases / Q000175:diagnosis / Q000235:genetics / Q000473:pathology
D016632:Apolipoprotein A-I