Subacute sclerosing panencephalitis (SSPE) or Dawson's encephalitis is a chronic debilitating disorder of the central nervous system characterized by progressive cognitive impairment, myoclonic jerks, extra‐pyramidal symptoms and classical high‐amplitude generalized periodic slow‐wave discharges also known as Rademecker complexes in electroencephalogram (EEG). A plethora of abnormal movements can occur in SSPE which include myoclonus, dystonia, tremor, chorea, rigidity, bradykinesia, ataxia and stereotypy. 1 The differential diagnosis of myoclonus in children/adults in the presence of EEG changes is rather specific, whereby in some cases findings in EGG may be pathognomonic. Here we present two cases with progressive cognitive impairment, jaw‐myoclonus and characteristic EEG findings diagnosed with SSPE.
Case 1
A 6‐year‐old girl, born to non‐consanguineous parents had a normal birth and developmental history. Two and half months before her visit, she started experiencing progressive cognitive impairment accompanied by jerky movements in her right limbs and shortly after also involuntary jaw opening. She did not have a history of headache, seizure, altered behavior, tremor, dysphagia, or urinary or bowel disturbances. There was also no history of febrile exanthem, trauma, or previous vaccination. At the time of visit, she was unresponsive to verbal commands but showed spontaneous eye opening and limb movements. Neurological examination revealed symmetric lead‐pipe rigidity, generalized hyperreflexia, and extensor plantar response. She exhibited quasi‐periodic, sudden jerky movement of the jaw and right upper and lower limbs with slow relaxation. (Video 1). The most likely differential diagnoses were meningoencephalitis, autoimmune encephalitis, and progressive myoclonic epilepsy. Her hematological and biochemical investigations including autoimmune work‐up and lactate level, showed no abnormalities. Cerebrospinal fluid (CSF) examination showed five cells (80% mononuclear), protein 67.4 mg/dL, glucose 57.8 mg/dL (blood glucose 90 mg/dL). CSF IgM‐ELISA for Japanese encephalitis, and PCR for Herpes Simplex, and Enterovirus were negative. Brain MRI showed non‐enhancing posterior‐predominant symmetric white‐matter T2/FLAIR hyperintensities with left fronto‐parietal atrophy (Fig. 1A,B), and an electroencephalogram showed Rademecker complexes (Fig. 1C). CSF Immunoglobulin‐G (IgG) titers for measles were highly elevated (13 NTU) with a positive IgG index (1.45). She was diagnosed with Jabbour stage‐III SSPE.
Video 1.
Video shows quasi‐periodic sudden, intermittent, rhythmic, and jerky opening of the jaw, lasting for 1–2 s followed by simultaneous jerky movement of the right upper and lower limb with slow relaxation. Second video shows involuntary jaw‐opening myoclonus accompanied by eye‐widening, giving a surprised look, followed by head and truncal‐negative myoclonus.
Figure 1.
MRI brain T2/FLAIR sequence shows (A) posterior‐predominant symmetric white matter hyperintensities, including right thalamus, (B) atrophy of left frontoparietal lobe, (C) Electroencephalography shows periodic high amplitude discharges lasting for 30–40 ms recurring in every 4–6 s interval with background slowing suggestive of Rademecker complexes.
Case 2
An 8‐year‐old girl presented with sudden episodes of jaw‐opening myoclonus accompanied by eye‐widening, giving a surprised look, followed by head and truncal‐negative myoclonus, and cognitive decline for the past 6 months. She reported frequent falls due to these myoclonic jerks. Brain MRI revealed T2/FLAIR hyperintensities in bilateral occipital white matter. Rademecker complexes on EEG and positive CSF IgG measles titers confirmed the diagnosis of SSPE (Video 1).
Both patients were treated with intrathecal Interferon‐alpha therapy and clonazepam 1.5 mg/day (in three divided doses) for 6 months. Although both cases experienced progressive deterioration of their clinical condition, the myoclonus responded to the treatment.
Abnormal jaw movements can include jaw dystonia (opening or closing), drug‐induced dyskinesia, jaw tremor, tics, chorea, and rarely jaw myoclonus, many of which are also encountered in SSPE. Myoclonus in SSPE may be generalized, multifocal, segmental, hemi‐ or focal. 2 The myoclonus in SSPE has been described as slow myoclonus, hung myoclonus, epileptic spasm, or periodic dystonic myoclonus. 3 Jaw‐opening myoclonus is a rare phenomenon in SSPE, and the exact site of origin of jaw myoclonus in SSPE is unknown. 4 However, the involvement of sensorimotor integration mechanisms has been suggested with contribution of basal ganglia ictal activity involving putamen, medial thalamus, and occipital lobes. 5
Here, we present two cases of rapidly progressing cognitive decline associated with striking jaw‐opening myoclonus in young children. Brain imaging and EEG provided key features to suspect the diagnosis, while CSF measles antibody titers confirmed SSPE. We suspect that the origin of myoclonus was subcortical in these cases. Further research is needed to determine if jaw‐opening myoclonus can be specifically attributed.
References
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