Enlarged SI and SII somatosensory evoked responses in the CLN5 form of neuronal ceroid lipofuscinosis Leena Lauronen a,b,c, * , J. Huttunen c,d , E. Kirveskari d , H. Wikstro ¨m c , K. Sainio d , T. Autti b , P. Santavuori a a Pediatric Neurology, Hospital for Children and Adolescents, University of Helsinki, Helsinki, Finland b Department of Radiology, Helsinki University Central Hospital, Helsinki, Finland c BioMag Laboratory, Medical Engineering Centre, Helsinki University Central Hospital, P.O. Box 340, 00029 Hus, Finland d Department of Clinical Neurophysiology, University of Helsinki, Helsinki, Finland Accepted 12 June 2002 Abstract Objectives: To examine in detail the activation of the primary (SI) and secondary (SII) somatosensory cortex in CLN5, the Finnish variant of late infantile neuronal ceroid lipofuscinoses (NCL). Methods: Somatory evoked magnetic fields were recorded with a 122-channel planar gradiometer in response to median nerve stimulation in 5 CLN5 patients (aged 8.8–16.7 years) and in 10 healthy age-matched controls. Results: The first two responses from contralateral SI, N20m and P35m, were 6–20 times stronger in the patients than in the controls. The morphology of the subsequent deflections from SI was abnormal in the patients: a prominent N45m was detected, while the normally present P60m deflection was missing. In 4 patients the contra- and in two patients the ipsilateral SII responses were also enlarged. Furthermore, the SII activation was detected at shorter latency in patients than in controls. Conclusions: At SI, CLN5 is associated with a selective enhancement of the early cortical responses. We propose that the enlargement of N20m most likely reflects increased synchronous input from thalamus, whereas the altered morphology of the following responses may reflect defective interneuronal inhibition at the cortex. The enlargement of SII responses shows that the imbalance between excitation and inhibition in CLN5 extends outside the primary somatosensory areas. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Somatosensory evoked response; Somatosensory cortex; Magnetoencephalography; Neuronal ceroid lipofuscinoses 1. Introduction Giant somatosensory evoked responses have been studied since 1947 when Dawson found an extremely high ampli- tude somatosensory evoked potential (SEP) in a patient with myoclonic epilepsy (Dawson, 1947). So-called giant SEPs are seen most often, but not exclusively, in patients with different forms of progressive myoclonus epilepsies (PME; Rothwell et al., 1984; Shibasaki et al., 1985; Miche- loyannis et al., 1989; Berkovic et al., 1991; Schmitt et al., 1994). However, not all patients with myoclonic epilepsies have giant SEPs (Shibasaki et al., 1985). Neuronal ceroid lipofuscinoses (NCLs) are autosomally recessively inherited progressive encephalopathies of child- hood, characterized by the accumulation of ceroid and lipo- fuscin-like material in storage cytosomes that leads to neuronal dysfunction and death. The characteristic symp- toms are epilepsy, mental retardation, motor symptoms and in most cases blindness. At least the infantile, late infan- tile and juvenile forms also present with myoclonus and are included in the group of progressive myoclonus epilepsies (Berkovic et al., 1991). However, giant SEPs have been described only in the late infantile forms (Harden and Pampiglione, 1982; Sainio, 1997). In magnetoencephalography (MEG), the neuronal sources underlying the recorded signals can be in many situations accurately modeled by means of, e.g., ensembles of equivalent current dipoles (ECD). For example, with MEG it is possible to disentangle the activities at the primary (SI) and at the secondary (SII) somatosensory cortex from each other (Hari et al., 1984). In different PME patient groups, the short-latency corti- cal somatosensory evoked magnetic fields (SEFs) from SI have been either normal or enhanced (Uesaka et al., 1993; Clinical Neurophysiology 113 (2002) 1491–1500 1388-2457/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S1388-2457(02)00200-6 www.elsevier.com/locate/clinph CLINPH 2001768 * Corresponding author (address c). Tel.: 1358-9-471-72092; fax: 1358- 9-471-75781. E-mail address: leena.lauronen@hus.fi (L. Lauronen).