Peripheral neuropathy as clinical onset of monoclonal IgM/k‐related amyloidosis.

Aim: Neuropathy is a frequent complication of Waldenström's macroglobulinemia (WM), the most common being a demyelinating polyneuropathy with anti‐myelin associated glycoprotein (MAG) antibodies, but also cryoglobulins, vasculitis, neurolymphomatosis, and amyloidosis. We describe a patient with IgM/kappa WM who presented with a severe, not length‐dependent, peripheral neuropathy as clinical onset of IgM/kappa‐related amyloidosis. Methods: A 69‐year‐old woman came to our attention for weight loss, gait imbalance and sensory loss at upper limbs. In her medical history, she was in hematological follow‐up for WM, and had undergone left carpal tunnel release. At neurological evaluation she had weakness and loss of sensation at upper limbs up to the elbows, more at the left side, gait was unsteady with right foot drop. Hypotrophy and areflexia were present at four limbs. Sensory loss and vibration sense were dramatically reduced. She underwent extensive diagnostic workup. Results: Laboratory workup revealed an IgM/kappa monoclonal paraprotein of 16 g/L and increased NT‐proBNP; anti‐MAG antibodies were absent. Bone marrow biopsy demonstrated a population of neoplastic B‐lymphocytes. Total‐body CT scan and echocardiogram were negative. Neurophysiology revealed a symmetric, no length dependent sensory‐motor polyneuropathy Periumbilical fat biopsy was positive for amyloid. Sural nerve biopsy detected amyloid in the wall of an epineurial vein. Conclusions: This case report describes a rare and unusual manifestation of IgM‐related AL amyloidosis in WM. The patient presented with a subacute clinically asymmetric neuropathy with no pain or dysautonomic features as clinical onset of IgM/kappa‐related amyloidosis. Sural nerve biopsy was crucial for the diagnosis. [ABSTRACT FROM AUTHOR]