Objective: N-methyl-D-aspartate receptor (NMDAR) encephalitis classically spans neuropsychiatric disturbance, autonomic dysfunction and salient movement disorders. Attenuated presentations are increasingly recognised; however, presentations with an isolated movement disorder are very rare.

Background: We describe a patient whose initial presentation was that of isolated craniocervical dystonia with serum and cerebrospinal fluid (CSF) NMDAR antibody positivity, without other manifestations of encephalitis

Method: .​​A 35-year-old female was referred with involuntary blinking and jaw clenching, followed by neck flexion progressing over months. There was no antecedent infection or systemic illness, and no psychiatric symptoms. Examination showed frequent blepharospasm (Video 1A) with subtle left torticollis and flexion. The remainder of the examination was normal. Antibody testing was requested due to the subacute presentation and progression over months. Anti-NMDA IgG was strongly positive in the CSF and weakly positive in serum. All other serological, CSF and imaging investigations were normal. She was treated with a combination of intravenous pulsed methylprednisolone, intravenous rituximab and monthly IVIg. Occasional visual hallucinations developed 6 months after initial symptom onset. At follow-up 2 years after diagnosis there was an ongoing cyclical response to IVIg, with re-emergence of dystonia in the days leading up to next infusion (Video 1C).

Results: NMDAR encephalitis presenting as a subacute isolated dystonia without cognitive or psychiatric features at early disease stage, is extremely rare, with only one previous report of a young female manifesting isolated left hemidystonia and rapid response to immunotherapy.[1] The strongly positive NMDAR antibodies in both serum and CSF, sustained clinical improvement with immunotherapy and cyclical response to IVIg, despite a lack of early psychiatric features, supports the likely pathological role of NMDAR antibodies in this case.

Conclusion: We suggest clinicians be aware of the rare occurrence of isolated dystonia associated with NMDAR antibodies, given its therapeutic implications. This case further expands the spectrum of NMDAR encephalitis, and antibody testing should be considered even in cases of isolated dystonia, if of subacute onset.

References: 1. Rubio-Agustí I, Dalmau J, Sevilla T, et al. Isolated hemidystonia associated with NMDA receptor antibodies. Mov Disord 2011;26(2):351-352

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MDS Abstracts - https://www.mdsabstracts.org/abstract/isolated-craniocervical-dystonia-without-neuropsychiatric-manifestations-associated-with-nmda-receptor-antibodies/