Slow periodic myoclonus (up to 1 second in duration) is a distinctive phenomenology described in fulminant subacute sclerosing panencephalitis (SSPE).1 We describe slow axial myoclonus in 2 children having SSPE (Videos 1 and 2). The slow myoclonus causes sudden alteration in tone of axial musculature, causing head drop or backward and sideways tilting of the trunk (axial tilt sign). The involvement of sensorimotor integration mechanism and basal ganglia ictal activity have been proposed as possible mechanisms for the periodic dystonic myoclonus.2 Basal ganglia involvement may also be responsible for associated dystonia. Fulminant Wilson disease and nonrhythmic, repetitive axial myoclonic jerks of propriospinal origin are important differential diagnoses.3,4
Video 1
Case 1: a 10-year-old boy with slow axial myoclonus and head drop. A 10-year-old boy with a history of measles in childhood (age around 15 months) presented with recent onset progressive cognitive decline, seizures, and periodic slow myoclonus in axial muscles—causing the neck and trunk to fall back. In addition, there was segmental myoclonic in neck and upper limbs—synchronous in flexor muscles, classic of SSPE. Myoclonic jerks were also noted while walking (see the last few seconds of the video), but they did not cause a fall. MRI brain screening was normal. EEG showed high amplitude, generalized spike, and wave periodic discharges. The diagnosis of “probable” SSPE was established using Dyken criteria (periodic, stereotyped, high voltage discharges + positive CSF antimeasles antibody).Download Supplementary Video 1 via http://dx.doi.org/10.1212/201283_Video_1
Video 2
Case 2: a 9-year-old girl with slow axial myoclonus and axial tilt sign. A 9-year-old girl, never vaccinated and with a history of fever in infancy, presented with recent onset cognitive decline, ataxia, and abnormal movements. The video shows repetitive, periodic, slow myoclonic movements in axial muscles causing tilting of trunk backward and to left (axial tilt sign). She also has dystonia in hands and toes, along with slow segmental myoclonic jerks involving flexor muscles of lower limbs. These myoclonic jerks do not interfere with consciousness and do not cause her to fall while walking. A noncontrast CT scan of brain did not show any major abnormality. A diagnosis of “probable” SSPE was made using Dyken criteria (periodic sharp-slow wave discharges + positive CSF antimeasles antibody).Download Supplementary Video 2 via http://dx.doi.org/10.1212/201283_Video_2
Study Funding
No targeted funding reported.
Disclosure
The authors report no relevant disclosures. Go to Neurology.org/N for full disclosures.
Acknowledgment
Dr. Jitendra Kumar Sahu, Professor of Paediatric Neurology, PGI Chandigarh, for helping in planning management of these cases.
Appendix Authors
Footnotes
Go to Neurology.org/N for full disclosures.
Submitted and externally peer reviewed. The handling editor was Whitley Aamodt, MD, MPH.
Teaching slides links.lww.com/WNL/C315
- Received January 11, 2022.
- Accepted in final form August 9, 2022.
- © 2022 American Academy of Neurology
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