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Tumefactive demyelination represents an aggressive form of demyelination that can rarely be paraneoplastic in origin. We report a case of paraneoplastic tumefactive demyelination caused by testicular seminoma in association with leucine zipper 4 (LUZP4) antibody.

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A 60-year-old man with history of long-standing unilateral testicular sensitivity presented with two weeks of progressive left-sided hemibody weakness, dysarthria, and an incongruous left homonymous hemianopsia. Brain MRI demonstrated a T2/FLAIR-hyperintense lesion involving the right cerebral peduncle and extending into the internal capsule, optic radiation, and dorsal midbrain, with mixed diffusion restriction and facilitation and an incomplete rim of peripheral enhancement. CSF studies were notable for elevated protein and increased IgG synthesis but absent pleocytosis and negative oligoclonal bands, flow cytometry, and cytology. During his hospitalization, his left-sided weakness worsened; short-interval repeat imaging showed expansion of the brainstem abnormality, concerning for an atypical inflammatory disorder. Systemic work-up, including scrotal ultrasound and body PET/CT, revealed a mass-like testicular lesion suggestive of a “burnt out” germ cell tumor and an FDG-avid retroperitoneal lymph node, with biopsy of the latter showing metastatic seminoma. Serologic and CSF antibody testing ultimately returned positive for LUZP4 IgG. He was treated for paraneoplastic tumefactive demyelination with pulse-dose IV steroids, IVIG, and malignancy-directed chemotherapy, with improvement in his vision and strength.

Paraneoplastic tumefactive demyelination is a rare disorder that can present as a complication of metastatic seminoma. LUZP4 IgG has been recently described as a novel biomarker for paraneoplastic syndromes, including rhombencephalitis, with high predictive value for associated testicular germ cell tumors. In cases of clinically atypical demyelinating disease, careful systemic evaluation is warranted to assess for occult malignancy, as neurologic outcome for patients with paraneoplastic syndromes depends on prompt and targeted oncologic management.