Reply to the Comment: On the Use of the Term “Epileptic Spasms” in Subacute Sclerosing Panencephalitis

10.1055/a-2810-4376

We thank Drs. Fusco and Specchio for their careful reading of our article and for their interesting comments regarding the terminology used for describing the motor phenomena observed in subacute sclerosing panencephalitis (SSPE).[1] We highly appreciate their expertise and welcome the opportunity to clarify our position.

We fully agree that motor phenomena in SSPE constitute a unique and distinctive electroclinical entity, closely related to periodic electroencephalogram (EEG) complexes and that inaccurate terminology may contribute to diagnostic confusion. Our intention was not to equate these events with classic epileptic spasms as defined in West syndrome or other developmental epileptic encephalopathies, nor to apply a syndromic seizure label. Rather, our primary aim was to highlight the limitations of the term myoclonus, which remains widely used in SSPE despite inconsistent electrophysiological support.

In our patient, the abnormal movements consisted of repetitive motor events lasting approximately 0.5 to 1 second, associated with a progressive electromyography (EMG) recruitment and relaxation forming a diamond-shaped pattern, related to diffuse slow EEG activity followed by attenuation. These characteristics differ from typical myoclonic jerks, which are brief, sharply phasic, and associated with short EMG bursts. From a descriptive electroclinical perspective, the duration and EMG morphology of these events are closer to spasm-like motor phenomena, as previously described in SSPE using EEG–EMG recordings.

As correctly mentioned by Fusco and Specchio, SSPE motor events often show a rigid periodicity and a fixed temporal relationship with periodic EEG complexes, suggesting a stable pathological generator rather than the dynamic epileptic networks classically underlying epileptic spasms. We fully acknowledge this distinction, and we fully agree that SSPE-related motor phenomena cannot be directly assimilated into existing seizure categories defined by the International League Against Epilepsy classifications.

However, historical and more recent electrophysiological studies have consistently underlined the prolonged nature and complex EMG morphology of SSPE motor events, using terms such as “periodic spasms,” “complex spasms,” or “spasm-like activity,” while also questioning the adequacy of the term myoclonus.[2] [3] [4] [5] Our use of the term epileptic spasms was therefore intended in a descriptive electroclinical sense, based on EMG duration and morphology, and not as a strict syndromic classification.

We believe that both contributions converge on the essential message that SSPE motor manifestations are unique and that the traditional use of the term myoclonus is insufficient and potentially misleading. Whether these events are best described as “spasm-like phenomena” or “SSPE-specific periodic motor events,” their accurate electroclinical documentation is essential to improve early recognition and understanding of this devastating disease.

We thank Drs. Fusco and Specchio for their valuable comments, which contribute constructively to advancing the discussion on SSPE motor manifestations.

Publication History

Article published online:
26 February 2026

• Reference

• 1 Fusco L, Specchio N. On the use of the term “epileptic spasms” in subacute sclerosing panencephalitis. Neuropediatrics 2026;
• 2 Pampiglione G. Polymyographic studies of some involuntary movements in subacute sclerosing pan-encephalitis. Arch Dis Child 1964; 39 (208) 558-563
• 3 Westmoreland BF, Sharbrough FW, Donat JR. Stimulus-induced EEG complexes and motor spasms in subacute sclerosing panencephalitis. Neurology 1979; 29 (08) 1154-1157
• 4 Ser MH, Gündüz A, Demirbilek V. et al. Progression of myoclonus subtypes in subacute sclerosing panencephalitis. Neurophysiol Clin 2021; 51 (06) 533-540
• 5 Eisermann M. Les spasmes épileptiques à début tardif. Epileptologie 2013; 30: 61-71