Novel imaging techniques using ¹⁸F-florbetapir PET/MRI can guide fascicular nerve biopsy in amyloid multiple mononeuropathy

Background: Multiple mononeuropathy is a rare presentation of primary (AL) amyloidosis and nerve biopsy is usually needed for diagnosis. Conventional imaging is useful to identify proximal nerve involvement but may be inadequate. We report a patient with multiple mononeuropathy whose presentation was suggestive of AL amyloid neuropathy and in whom repeated tissue biopsies were negative for amyloid (including two sensory nerves and one muscle). Methods: The patient underwent magnetic resonance imaging (MRI) and whole body ¹⁸F-florbetapir positron emission tomography (PET)/MRI. Results: Whole body ¹⁸F-florbetapir PET/MRI revealed abnormal low-level florbetapir uptake in the right proximal tibial and peroneal nerves, which provided a target for a sciatic bifurcation fascicular nerve biopsy that was diagnostic of AL amyloidosis. Conclusions: ¹⁸F-florbetapir PET/MRI imaging is a promising diagnostic tool for patients with suspected peripheral nerve amyloidosis (including multiple mononeuropathy) in whom conventional imaging and nerve and muscle biopsies miss the pathology.