Dyck, P. James B.

ABSTRACT Background and Aims Nonsystemic vasculitic neuropathy classically presents as a painful asymmetric axonal neuropathy, multiple mononeuropathies or radiculoplexus neuropathy. Demyelinating electrophysiologic features are rare and may lead to misdiagnosis. We describe a patient with biopsy‐proven vasculitic neuropathy presenting as a severe symmetric demyelinating polyradiculoneuropathy. Methods Clinical, electrophysiologic, imaging, laboratory, and histopathologic findings are presented. Results A 57‐year‐old man developed acute ascending weakness, sensory loss, facial weakness, and areflexia following a febrile illness, with initial improvement before developing recurrent neurological decline 6 weeks after initial symptom onset despite treatment with intravenous immunoglobulin and plasma exchange. Cerebrospinal fluid protein was elevated. Nerve conduction studies demonstrated prolonged distal motor latencies, slowed conduction velocities, conduction block, and prolonged blink reflex latencies, fulfilling 2021 European Academy of Neurology/Peripheral Nerve Society electrodiagnostic criteria for chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). MRI demonstrated mild but diffuse lumbosacral plexus enlargement and T2 hyperintensity. Sural nerve biopsy ultimately demonstrated evidence of epineurial inflammation and microvasculitis with ischemic nerve injury, accompanied by both increased rates of axonal degeneration (12%) and segmental demyelination (9%) on teased fiber analysis. Treatment with corticosteroids and rituximab resulted in complete neurological recovery. Interpretation Vasculitic neuropathy may closely mimic CIDP clinically, radiologically, and electrophysiologically. Clues to the vasculitis diagnosis were prominent neuropathic pain, dense denervation on electrophysiology, and poor response to typical CIDP treatment. Peripheral nerve biopsy remains a critical tool in the evaluation of atypical or treatment‐refractory inflammatory neuropathies.

BACKGROUND MRI-guided targeted fascicular biopsy has been a valuable technique for diagnosing idiopathic neuropathies. It has an 80% yield and a minor permanent morbidity rate of 5%. OBSERVATIONS A 48-year-old woman with a history of localized amyloidosis to the orbital muscle 2 years earlier presented with new neurological symptoms. Extensive evaluations including skin, muscle, and distal cutaneous nerve biopsies were negative, and empirical treatment trials did not improve her condition. An MRI-guided targeted biopsy of the right ulnar nerve in the distal arm was planned. During surgery, a medial triceps branch arising from the ulnar nerve was identified and was biopsied along with a neighboring fascicle of the ulnar nerve to the flexor carpi ulnaris. The pathology of the ulnar nerve fascicle but not the contiguous triceps branch showed amyloid (AL [kappa] subtype on mass spectroscopy). The patient was started on treatment. LESSONS The positive biopsy of the ulnar nerve fascicle allowed targeted treatment of the neural amyloidosis. While the negative biopsy of the triceps branch could be attributed to sampling error, it could also be due to the fact that this branch found within the ulnar nerve is thought to originate from the radial nerve. https://thejns.org/doi/10.3171/CASE25484