Objective: To describe a case of anti-Hu/ANNA-1 Opsoclonus-Myoclonus syndrome (OMS) in a patient with small cell lung cancer (SCLC) after treatment with an immune checkpoint inhibitor (ICI).

Background: Anti-Hu syndrome is highly associated with malignancy, particularly with SCLC. Anti-Hu antibodies have been associated with several defined syndromes, including OMS. We present a case of a 59-year-old female with a history of SCLC who initially presented with encephalopathy, bilateral facial pain, and concern for seizures. The patient had completed chemotherapy and whole brain radiation treatment and was undergoing immunotherapy with atezolizumab which was last received 3 weeks prior to presentation. Her cancer was noted to be in remission. Her neurological exam was notable for opsoclonus and myoclonic jerks involving her upper extremities.  Magnetic resonance images with and without contrast of her brain and spine were notable for cauda equina enhancement. Electroencephalogram showed no epileptiform changes. Anti-Hu antibodies were positive with a serum titer of 1:30720 and cerebrospinal fluid titer of 1:4096. She was treated with alternating intravenous (IV) steroids and IV immunoglobulin with minimal improvement in her symptoms. However, treatment was initiated about one month after symptom onset.

Method: N/A

Results: N/A

Conclusion: Anti-Hu syndrome has several manifestations described in this case including encephalopathy with seizures, facial pain, OMS, and cauda equina enhancement. The patient’s malignancy was noted to be in remission with treatment to date. Literature notes few cases of ICI-induced paraneoplastic syndromes with potential for poor prognoses even with treatment. Standard management guidelines are yet to be established, and early recognition is crucial in minimizing long-term neurological complications.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-rare-case-of-anti-hu-opsoclonus-myoclonus-syndrome-after-immune-checkpoint-inhibitor-immunotherapy-in-a-patient-with-small-cell-lung-cancer-in-remission/