Abstract Details

Title Antibody-negative Paraneoplastic Granulomatous Rhombencephalitis associated with Primary Mediastinal Seminoma

Topic Autoimmune Neurology

Presentation(s) P3 - Poster Session 3 (11:30 AM-12:30 PM)

Poster/Presentation
Number 1-039

Objective Describe an unusual presentation of antibody-negative rhombencephalitis with
granulomatous pathology associated with mediastinal seminoma.

Background Neurologic syndromes associated with seminoma are typically antibody-mediated, most
commonly linked to KLHL11, and usually present as limbic or brainstem encephalitis.
Granulomatous CNS inflammation has not been well described in this setting.

Design/Methods CASE REPORT

Results A 33-year-old male presented with subacute diplopia, vertigo, and gait ataxia following
several months of constitutional symptoms, including weight loss. MRI brain showed a
T2/FLAIR hyperintense lesion involving the right dorsal medulla, cerebellopontine angle,
and cerebellum, with associated nodular enhancement. CSF demonstrated lymphocytic
pleocytosis with elevated protein and a persistent unique oligoclonal band. Extensive
infectious, rheumatologic, and paraneoplastic antibody testing, including KLHL11 and
Ma2 in serum and CSF, was negative, with no evidence of neuronal staining on
composite tissue. Despite initial clinical improvement with corticosteroids, imaging
demonstrated radiologic progression. Brain biopsy revealed necrotizing granulomatous
inflammation, with broad infectious and neoplastic evaluation, including PCR and
metagenomic next-generation sequencing, unrevealing. Whole-body PET-CT imaging
revealed two hypermetabolic anterior mediastinal nodules, and surgical resection
confirmed a primary mediastinal seminoma. Testicular ultrasound was negative. The
patient demonstrated marked clinical and radiographic improvement with
corticosteroids, cyclophosphamide, and chemotherapy.

Conclusions This case highlights a steroid-responsive rhombencephalitis with biopsy-proven granulomatous inflammation occurring in association with primary mediastinal seminoma. In the absence of an identifiable infectious or systemic granulomatous process, findings support a paraneoplastic immune-mediated mechanism. This expands the spectrum of seminoma-associated neuroimmunologic disease and underscores the value of comprehensive malignancy screening and early tissue diagnosis (low threshold to biopsy) in atypical CNS inflammatory presentations.

Authors/Disclosures
Kyle Alexander, MD PRESENTER	Kyle Alexander has nothing to disclose.
Sydney Lee, MD (University of Utah)	Dr. Lee has nothing to disclose.
Thomas V. Varghese, Jr., MD, MS, MBA	Dr. Varghese has received personal compensation in the range of $50,000-$99,999 for serving as an Editor, Associate Editor, or Editorial Advisory Board Member for Journal of the American College of Surgeons.
Tammy L. Smith, MD, PhD (Imaging and Neurosciences Center)	Dr. Smith has received personal compensation in the range of $5,000-$9,999 for serving on a Scientific Advisory or Data Safety Monitoring board for EMD Serono. The institution of Dr. Smith has received research support from Alexion/AstraZeneca.
Stacey Clardy, MD, PhD, FAAN (University of Utah)	Dr. Clardy has received personal compensation for serving as an employee of Veterans Health Administration (VHA). Dr. Clardy has received personal compensation for serving as an employee of University of Utah Health. Dr. Clardy has received personal compensation in the range of $5,000-$9,999 for serving on a Scientific Advisory or Data Safety Monitoring board for AstraZeneca/Alexion. Dr. Clardy has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Amgen/Horizon. Dr. Clardy has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Arialys. Dr. Clardy has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Kyverna. Dr. Clardy has received personal compensation in the range of $10,000-$49,999 for serving as an Editor, Associate Editor, or Editorial Advisory Board Member for Neurology/AAN Publications. The institution of Dr. Clardy has received research support from NIH/NINDS. The institution of Dr. Clardy has received research support from SRNA. The institution of Dr. Clardy has received research support from Alexion/AstraZeneca. The institution of Dr. Clardy has received research support from Kyverna. Dr. Clardy has received personal compensation in the range of $500-$4,999 for serving as a AAN Summer Meeting CoDirector Travel and Lodging with AAN. Dr. Clardy has received personal compensation in the range of $500-$4,999 for serving as a Grand Rounds Travel/Lodging/Honoraria with U of Iowa, Miami, Stanford, Barrow, Advent Health Florida, Beaumont Health, CCF, Emory, Penn State Health, Mayo Clinic, Walter Reed.

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