RESUMEN
Paraneoplastic cerebellar degeneration (PCD) is one of the most prevalent neurological paraneoplastic syndromes, typically associated with small cell lung cancer (SCLC). PCD is thought to be caused by proteins expressed by tumor cells which trigger an antibody-mediated immune response. Despite PCD being commonly associated with anti-Yo, anti-Hu and anti-Tr/DNER antibodies, PCD is the most prevalent paraneoplastic syndrome in patients harboring anti-Zic4 antibodies. We report what, to our knowledge, is the first known case of anti-Zic4 mediated PCD in a patient with EGFR-mutated metastatic non-small cell lung cancer (NSCLC). Our patient was in complete response (CR) to targeted therapy and presented to the emergency room with drowsiness, unsteady gait and memory lapses. The diagnostic work-up revealed a diffuse cerebellar atrophy in the MRI, ruling out brain metastasis and leptomeningeal carcinomatosis. A body-CT scan showed no signs of recurrent disease. The cerebrospinal fluid (CSF) was within normal parameters. An onconeural antibody panel was conducted in a peripheral blood sample, detecting high levels of anti-Zic4 antibody by indirect immunofluorescence (IFI), results later confirmed by immunoblot testing. With the suspected diagnosis of an anti-Zic4 PCD, the case was discussed with the neurology department and treatment with high dose methylprednisolone was initiated. Considering the lack of substantial clinical benefit, the patient was then treated with intravenous immunoglobulins (IVIG) for 5 days, showing modest improvement. At this time, the patient presented minor disease relapse in the form of a sub-centimetric pulmonary nodule. Despite one cycle of chemotherapy, the patient's neurological condition deteriorated leading to fatal pneumonia secondary to progressive dysphagia. There is scarce evidence of paraneoplastic syndromes in EGFR-mutated NSCLC. Further research is warranted to stablish a possible association between anti-Zic4 and the EGFR molecular pathway.