A Rare Case of Brain Biopsy-confirmed Neurolymphomatosis Involving the Central Nervous System Mimicking Polyneuropathy as a Complication of Refractory Sjögren's Syndrome.

Neurolymphomatosis is a rare lymphoma infiltrating cranial nerves, peripheral nerves, and spinal nerve roots. We present a unique case of neurolymphomatosis involving the central nervous system, initially resembling polyneuropathy in Sjögren's syndrome. A 79-year-old woman experienced dry eye symptoms for 2 years before presenting with left facial nerve palsy and lumbar pain to her previous physician. Brain magnetic resonance imaging revealed high signal intensity on diffusion-weighted imaging solely in the left peripheral facial nerve and lower cranial nerves. Initially diagnosed with Sjögren's syndrome-associated polyneuritis, she underwent treatment with high-dose steroid pulse therapy and intravenous immunoglobulin. Despite treatment, her symptoms progressed, leading to referral to our hospital with multiple peripheral nerve palsies and severe lumbar pain. Subsequent brain magnetic resonance imaging demonstrated gadolinium enhancement in the bilateral caudate nucleus heads and the left facial and lower cranial nerves. Stereotactic brain tumor biopsy-confirmed diffuse large B-cell lymphoma upon pathological analysis. Treatment with rituximab, high-dose methotrexate significantly improved her symptoms, with no recurrence observed for 12 months. These findings underscore the diagnosis of neurolymphomatosis involving the central nervous system, initially masquerading as Sjögren's syndrome. Neurolymphomatosis should be considered in cases of refractory Sjögren's syndrome presenting with multiple nerve palsies.