Objective: To describe a rare case of delayed parkinsonism emerging during the recovery phase of anti‑NMDAR encephalitis following immunotherapy in a young adult woman.

Background: Anti‑NMDAR encephalitis is an autoimmune encephalitis characterized by prominent psychiatric symptoms, seizures, and diverse movement disorders, most commonly hyperkinetic phenomena. Parkinsonism, although recognized within the movement disorder spectrum of this condition, is an uncommon and under‑reported manifestation. The underlying mechanisms remain unclear and may involve persistent immune-mediated dysfunction of basal ganglia circuits

Method: A 21‑year‑old woman was admitted with altered mental status occurring two weeks prior to admission, characterized by aggression and hallucinations, followed by the first episode of seizure. No clinical improvement was observed after antiviral and steroid treatment. On week 2, observable lip‑smacking movements were noted. Cerebrospinal fluid (CSF) analysis was performed and tested positive for anti‑NMDA receptor antibodies. Abdominal CT revealed a mature teratoma on the left adnexa. The symptoms were gradually improved after rituximab treatment and teratoma removal surgery. Her overall condition continued to improve, after receiving rituximab and undergo tumor resection surgery. However, on week 9, parkinsonism was noted in both extremities

Results: By week 11, the patient’s condition kept improving. The patient had adequate contact, no fever, no seizures, no movement of the lower jaw or tongue. Tremors in both upper limbs persisted but were only present as action tremors. Rigidity was still positive, but eventually kept improving. Therefore, the patient was discharged.

Conclusion: This case illustrates that delayed parkinsonism can occur during the recovery phase of anti‑NMDA receptor encephalitis after immunotherapy and tumor surgery. Long‑term monitoring for hypokinetic movement disorders is warranted in these patients, as early recognition may guide symptomatic management and improve functional outcomes.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/delayed-parkinsonism-in-anti-nmdar-encephalitis-following-immunotherapy-a-rare-clinical-manifestation/