INTRODUCTION
Leptomeningeal metastasis (LM) is an extremely rare complication of gastroesophageal (GE) cancer. Diagnosis is challenging due to frequently nonspecific clinical presentations, limited sensitivity of diagnostic testing, and potential overlap with neurologic immune-related adverse events (irAE). We describe a case of metastatic gastroesophageal cancer on immunotherapy presenting with LM masquerading as polyneuropathy.
CASE REPORT
A 74-year-old male with HER2+ GE junction cancer with peritoneal metastases diagnosed 6 months ago, on maintenance trastuzumab/pembrolizumab and with no previous history of cranial or spinal disease, presented with worsening ataxia, headache, and diplopia for one month with multiple negative outpatient MRIs. Examination showed left abducens nerve palsy, dysmetria and absent deep tendon reflexes in upper and lower extremities. CT head was unremarkable, and MRI showed non-specific mild enhancement of the right optic nerve, symmetrical lumbosacral nerve roots and cauda equina concerning for paraneoplastic versus immunotherapy-related polyneuropathy. He was started on empiric high-dose corticosteroids. PET-CT was negative for FDG-avid lesions. Cerebrospinal fluid (CSF) analysis revealed moderate pleocytosis with many large atypical cells, elevated protein (118 mg/dL) and LDH (28 IU/L). Immunohistochemistry was positive for CDX2, CA 19-9, CK7, and pankeratin, consistent with metastatic adenocarcinoma, negative for HER2 in contrast to the original tumor. He subsequently developed hydrocephalus requiring a ventriculoperitoneal shunt. He received ten fractions of whole brain irradiation before electing to pursue hospice care.
DISCUSSION
LM is an extremely rare complication of GE cancer with an incidence of <0.2% and carries a poor prognosis. Differentiation between LM and irAE in patients on immunotherapy can be challenging. Diagnosis relies mostly on CSF cytology, and lumbar puncture should not be delayed in patients with new neurologic symptoms. Treatment options are intrathecal chemotherapy, radiation and steroids. A recent phase II trial has shown promise for intrathecal trastuzumab in patients with HER2+ cancers, but options for HER2 negative disease remain mostly palliative.
CONCLUSIONS
Our case highlights the need for suspecting this rare metastatic site, as early diagnosis and genetic characterization allow for exploring more treatment options including targeted therapies which may improve overall survival and quality of life.
