Jaw Opening Myoclonus in Subacute Sclerosing Panencephalitis: A New Phenotypic Observation
Article information
Dear Editor,
Subacute sclerosing panencephalitis (SSPE) is a neurodegenerative disorder due to persistent infection of the brain with a mutant measles virus, with clinical signs emerging in late childhood and adolescence. The phenotypic sine qua non is the presence of a slow axial myoclonus. Movement disorders are seen in up to half of all patients with SSPE [1]. We have recently reported jaw myoclonus for the first time in SSPE [2] and have subsequently observed it in other patients.
A cross-sectional study was conducted between November 1, 2020, and August 31, 2022. During this period, 56 patients with SSPE were identified at Kalawati Saran Children’s Hospital, New Delhi, India. SSPE diagnosis was based on a modified form of Dyken’s criteria.
The median age (range) at presentation was 6 years (2.5 months–19 years), and the median age at onset was 5.9 (1.5–17.6) years. The median disease duration was 0.3 (4–36) months. The median Jabbour stage was 2 (2–5). Of 56 patients, seven (12.5%), including 5 males, demonstrated jaw opening myoclonus (JOM) (Table 1, Supplementary Videos 1-6 in the online-only Data Supplement). The age range was 3–18 years. The median duration of symptoms was 4 (1.5–24) months. Five patients were in Jabbour stage 3. All patients also demonstrated myoclonus in other body regions. JOM was synchronous with myoclonus in other regions in five patients and asynchronous in two. In one patient, JOM followed myoclonus in other body regions. Ocular myoclonus was observed in two patients (Cases 2 and 3) and was synchronous with JOM in both. Associated dystonia was seen in four patients. In two patients, JOM was seen despite normal magnetic resonance imaging (MRI) and a lack of periodic electroencephalography (EEG) discharges. Apart from the median Jabbour stage, which was higher in patients with JOM, we did not find any significant differences in terms of EEG or MRI compared to the patients without JOM.
Detailed characteristics of SSPE patients with jaw myoclonus
The typical SSPE myoclonus is periodic, axial, and stereotyped, with a slow relaxation phase. Jaw myoclonus is a new phenotypic observation that may assist in disease recognition, especially when MRI and EEG do not contribute to the evidence of SSPE. Jaw myoclonus may be a feature of advanced disease in SSPE. The origin of myoclonus in SSPE has been debated but may correlate with the disease stage, with cortical or cortico-subcortical origin in earlier stages and brainstem origin in advanced stages, suggesting a cephalocaudal spread of pathology [3]. In our series, we considered the patients’ abnormal jaw movement to be myoclonus rather than dystonia, despite its slow character. The slowness of the relaxation phase was consistent with the typical presentation of SSPE myoclonus.
Involuntary movement involving the jaw has been reported in other conditions: jaw myoclonus induced by drugs such as cefepime and gabapentin [4], jaw closure myoclonus in sleep-related faciomandibular myoclonus [5], and jaw closure dystonia in anti-Ri-related encephalitis [6].
However, in our experience, jaw-opening myoclonus seems to be exclusive to patients with SSPE as opposed to any other disease involving the jaw. As slow myoclonus in SSPE serves as a diagnostic hallmark, jaw-opening myoclonus may have additional diagnostic potential. We do not know at what point in the disease course jaw myoclonus first appears. It would be useful to track the disease longitudinally and assess whether jaw myoclonus provides any prognostic value.
Supplementary Material
The online-only Data Supplement is available with this article at https://doi.org/10.14802/jmd.23158.
Video 1.
Case 1. An 18-year-old male with recurrent jaw opening, limb and axial myoclonus, tremors and retrocollis.
Video 2.
Case 2. An 18-year-old male with recurrent jaw opening and limb myoclonus, right upper limb dystonia and forced deviation of the contralateral eye.
Video 3.
Case 3. A 6-year-old male with recurrent jaw-opening myoclonus accompanied by ocular myoclonus with gaze direction to the left.
Video 4.
Case 4. A 9-year-old male with jaw-opening myoclonus synchronized with right upper limb myoclonus.
Video 5.
Case 5. A 3-year-old female with recurrent jaw opening following limb myoclonus and left-sided dystonia.
Video 6.
Case 6. A 12-year-old male with jaw-opening myoclonus synchronized with left upper and lower limb myoclonus.
Notes
Ethics Statement
This study was approved by the Lady Hardinge Medical College Institutional Ethics Committee (Reference no. F.LHMC/IEC/2022/03/31). Informed consent was obtained from the participant’s parents and assent from the child, whenever applicable. We confirm that we have read the Journal’s position on issues involved in ethical publication and affirm that this work is consistent with those guidelines.
Conflicts of Interest
The authors have no financial conflicts of interest.
Funding Statement
None
Author contributions
Conceptualization: Divyani Garg, Suvasini Sharma. Data curation: all authors. Formal analysis: Divyani Garg. Investigation: Suvasini Sharma. Methodology: Divyani Garg, Suvasini Sharma. Project administration: Suvasini Sharma. Resources: Suvasini Sharma. Software: Divyani Garg. Supervision: Suvasini Sharma. Validation: Vanshika Kakkar, Suvasini Sharma. Visualization: Divyani Garg, Suvasini Sharma. Writing—original draft: Divyani Garg. Writing—review & editing: Vanshika Kakkar, Suvasini Sharma.
Acknowledgements
We thank the patients and their families for their co-operation.