1H-MR spectroscopy indicates prominent cerebellar dysfunction in benign adult familial myoclonic epilepsy

Authors


Address correspondence to Pasquale Striano, MD, PhD, Muscular and Neurodegenerative Diseases Unit, “G. Gaslini” Institute, Genova, and Epilepsy Center, Federico II University, Napoli, Italy. E-mail: pstriano@email.it

Summary

Purpose:  To investigate the neurochemical pattern in patients with benign adult familial myoclonic epilepsy (BAFME/FAME), an inherited form of myoclonic epilepsy, by proton magnetic resonance (MR) spectroscopy (1H-MRS).

Methods:  Eleven BAFME patients from three families showing linkage to 2p11.1-q12.2 were compared with 11 age-matched healthy control subjects.

Results:  MR imaging of all the patients and healthy subjects exhibited no structural abnormalities on detailed visual assessment. However, compared with healthy subjects, patients with BAFME displayed elevated choline/creatine ratio in the cerebellar cortex (p = 0.01), whereas there was no significant difference for the other ratios. No 1H-MRS values in the frontal and occipital cortex differed significantly in the patients compared with the healthy controls. No correlation was detected between 1H-MRS values and disease duration (p = −0.35) as well as myoclonus severity (p = −0.48).

Conclusions:  Our findings suggest that the cerebellum is a prominent site of dysfunction in BAFME. The abnormal choline concentrations could reflect changes in the chemical and functional nature of cell membranes. 1H-MRS was able to detect brain changes also in patients with recent disease onset and may be a useful tool supporting the diagnosis based on familial and electrophysiologic data. The relationship between cortical tremor and the cerebellum is also discussed.

Benign adult familial myoclonic epilepsy (BAFME, OMIM 601068) or familial adult myoclonic epilepsy (FAME, OMIM 607876) is an autosomal dominant (AD) condition characterized by cortical tremor, myoclonus, and epilepsy (de Falco et al., 2003; Striano et al., 2005; Uyama et al., 2005). Cortical tremor consists of continuous, arrhythmic, distal twitches of the hands that may be distinguished from the more common essential tremor by electrophysiologic evidence of cortical reflex myoclonus and the lack of response to beta-blockers (Ikeda et al., 1990; Striano et al., 2005; Uyama et al., 2005). In addition, patients have myoclonus of the upper extremities and rare generalized tonic–clonic seizures often precipitated by sleep-deprivation or photic stimulation (Ikeda et al., 1990; Striano et al., 2005; Uyama et al., 2005). Drug-resistant partial seizures or slight mental retardation may be present in some patients, as reported in autosomal dominant cortical myoclonus and epilepsy (ADCME) (Guerrini et al., 2001). BAFME was first described and mapped on chromosome 8q in Japanese families (Mikami et al., 1999; Uyama et al., 2005). Subsequently, European kindreds have been reported (van Rootselaar et al., 2004; Striano et al., 2004, 2005; Gardella et al., 2006; Saint-Martin et al., 2008), and linkage to chromosome 2p11.1-q12.2 was shown in Italian pedigrees for some of which there is evidence of a common founder haplotype (Madia et al., 2008). Thus far, the pathophysiology of this condition remains speculative. The patients show the neurophysiologic features of cortical reflex myoclonus consistent with the hypothesis that cortical tremor is related to cortical motor hyperexcitability (Ikeda et al., 1990; Striano et al., 2005; Uyama et al., 2005). However, in the few cases that came to neuropathologic examination, a pattern of Purkinje cells and dendritic tree loss and Bergmann gliosis was evident, whereas sensorimotor cortex was normal (van Rootselaar et al., 2004, 2007a; Uyama et al., 2005). Therefore, frontal and cerebellar cortex is of major interest for an 1H-MRS study.

Unlike conventional magnetic resonance imaging (MRI), which provides structural information based on signals from water protons, proton MR spectroscopy (1H-MRS) is a powerful tool, which provides information about the chemical composition of the brain (Duncan, 1996; Kuzniecky, 2004; Hiremath & Najm, 2007). Three major peaks characterize long echo-time 1H-MRS spectra: N-acetylaspartate (NAA), creatine (Cr), and choline (Cho). NAA is localized exclusively in neurons and their processes throughout the central nervous system (CNS). Experimental and clinical work suggests that NAA is a marker of neuronal metabolic function, whereas the changes of Cho are mainly the result of failure of the oxygen-dependent synthesis of phosphorylcholine, a precursor of membrane formation (Duncan, 1996; Dautry et al., 2000; Long et al., 2000).

Here we report the data on 11 patients with BAFME who were evaluated by 1H-MRS study.

Subjects and Methods

Subject selection and evaluation

Eleven right-handed patients (eight men, three women; mean age 39.6 ± 16 years, range: 16–70) from three BAFME families showing AD inheritance and linkage to 2p11.1-q12.2 were investigated; characteristics of families have been described in detail elsewhere [family A (de Falco et al., 2003); family B (Striano et al., 2007); family C (Striano et al., 2004)]. All the kindreds originate from the region of Naples, Southern Italy, and share the same haplotype covering the “5332” of adjacent markers D2S388, D2S2216, D2S113, and D2S2175, suggesting a common founder effect (Madia et al., 2008). The demographic and clinical features of the patients are summarized in Table 1. Mean age at onset of cortical tremor was 22 ± 1.8 years (range: 15–30) and mean disease duration was 18 ± 14.7 years (range: 1–40). All the subjects had cortical tremor and myoclonus at the upper limbs. Rare generalized tonic–clonic seizures had occurred in five subjects. In all the patients the only remarkable feature at neurologic examination was the hand tremor. None of the patients showed mental retardation. Electrophysiologic study—including electroencephalography (EEG), jerk-locked averaging, somatosensory evoked potentials, and long-loop reflex I—showed generalized paroxysmal activity and evidence of cortical reflex myoclonus in all the subjects. Severity of myoclonus, assessed with the Unified Myoclonus Rating Scale (Frucht et al., 2002), ranged from 15–30 (mean: 24.2; ±8.2 SD). Therapy consisted of valproic acid in seven patients that was combined with clonazepam (n = 5) or levetiracetam (n = 4). One patient was treated with levetiracetam only. Three patients did not agree to receive any therapy. Eleven age-matched, right-handed, healthy volunteers (seven men, four women; mean age 38 ± 4.1 years, range 18–55) were also evaluated. The local ethics committee approved the study and written informed consent was provided by the participants.

Table 1.   Age, sex, and clinical characteristics of patients with benign adult familial myoclonic epilepsy (BAFME)
FamilyPatient ID/sex/age (years)Age at onset (years)Duration of illness (years)GTCSUMRS scoreTherapy
  1. GTCS, generalized tonic–clonic seizures; UMRS, Unified Myoclonus Rating Scale; LEV, levetiracetam; VPA, valproate; CNZ, clonazepam.

AIII:4/F/703040No35LEV
IV:2/F/461640Yes20VPA, CNZ, LEV
IV:4/F/383038No20VPA, CNZ
V:2/M/18153No15
V:3/M/17161No16
BIII:12/M/572334Yes35VPA, CNZ, LEV
III:4/M/472522Yes22VPA, CNZ, LEV
IV:1/M/412318Yes30VPA, CNZ, LEV
IV:6/M/18171No15
CIII:3/M/433013No35VPA, CNZ, LEV
III:4/M/411822Yes25VPA, CNZ

MRI and 1H-MRS protocol

Patients and controls underwent MRI and single-voxel 1H-MRS on a 1.5-T system (General Electric Signa Infinity HiSpeed SR77, Block Imaging International, Lansing, MI, U.S.A.) equipped with a circularly polarized head coil. To avoid movement artifacts, participants were asked to inhibit the hand tremulous movements by resting the upper limbs on the scanner bed. MRI protocol included sagittal T1-weighted fluid-attenuated inversion recovery (FLAIR; TR, 10,000 ms; TI, 560 ms; TE, 85 ms) and axial T2-weighted fast spin echo (FSE; TR, 4,250 ms; TE, 109 ms; ETL, 24 ms) images (slice thickness was 4 mm; field of view, 24 × 24 cm; and matrix size, 320 × 256). We also performed axial T1-weighted three-dimensional (3D)-FSPGR images (TR, 10 ms; TE, 4 ms; flip angle, 15 degrees; slice thickness, 2 mm; slices interpolated at 1 mm; field of view, 24 × 24 cm; matrix size, 224 × 224). For 1H-MRS, an automated single-voxel point-resolved spectroscopy (PRESS) sequence (probe-p) was applied with 128 averages and TR, 1,500 ms; TE, 144 ms. A time acquisition of 3.45 min was used. Volumes of interest (VOIs) of 8 cc (2 × 2 × 2 cm) were adjusted to individual anatomy on magnetization-prepared rapid gradient echo water excitation (MP-RAGE) images covering the frontal and occipital cortex, and the cerebellum (Fig. 1). The frontal VOI was placed anterior to the corpus callosum by using the plane of the anterior and posterior cerebral commissure as the caudal border, and including the craniolateral portion of the frontal lobe (Savic et al., 2000; Simister et al., 2003). The occipital VOI covered the Broadmann areas 17 and 18 and was selected as a presumably unaffected region. The cerebellar VOI was located lateral to dentate nuclei. Only the right side was examined because of the measuring time constraints. 1H-MRS spectroscopy provided spectra peak areas at 2.02, 3.02, and 3.22 ppm, corresponding to NAA, Cr, and Cho. The peak amplitude ratio was measured independently by two skilled operators (FC and RDB), who were blinded to the clinical data. NAA/Cr, NAA/Cho, and Cho/Cr ratios were analyzed. These ratios were calculated with the program SAGE (GEMS).

Figure 1.

 Location of the 8 cc (2 × 2 × 2 cm) voxels in right cerebellar, frontal, and occipital hemisphere axial T1-weighted images (left) with relative spectral peaks in a patient with benign adult familial myoclonic epilepsy (BAFME) (middle) and in a control (right). Note the abnormal spectral peak areas at 3.22 ppm corresponding to choline in the cerebellum ***[point-resolved spectroscopy (PRESS) sequence; TR 1,500 ms, TE 144 ms].

Statistical analysis

Statistical analysis was performed with MedCalc 9.2 (MedCalc Software, Mariakerke, Belgium). We employed the Mann-Whitney test to evaluate differences between patients and controls for 1H-MRS data. Correlation of parametric variables (i.e., disease duration and severity, 1H-MRS ratios) were analyzed with the nonparametric Spearman test (rho). The level of significance was set at p < 0.05.

Results

Morphologic and metabolite data on 1H-MRS

MRI of all the patients and of healthy subjects exhibited no abnormalities on detailed visual assessment, including multiplanar reformatting with thin cuts. As regards the 1H-MRS study, Table 2 shows the mean and standard deviation (SD) of NAA/Cr, NAA/Cho, and Cho/Cr ratios in patients and controls. The Cho/Cr ratio was significantly increased (p = 0.01) in the cerebellar cortex of the patients compared with the healthy controls (Fig. 2A), whereas no difference was observed for the NAA/Cr ratio (p = 0.56) (Fig. 2B). The NAA/Cho ratio was also decreased in patients compared with controls, but this was not statistically significant (p = 0.05) (Fig. 2C). One subject (patient V:3 of family A) showed abnormally increased Cho cerebellar concentrations [under the 95% confidence interval (CI)]. None of the 1H-MRS values in the frontal and occipital cortex differed significantly in the patients compared with the healthy controls (data not shown).

Table 2. 1H-MRS data in patients with benign adult familial myoclonic epilepsy (BAFME) and healthy controls
MRS dataPatientsControlsp-value
  1. MRS, magnetic resonance spectroscopy; NAA, N-acetylaspartate.

  2. The statistically significant p-value is shown in bold font.

Cerebellum
 NAA/creatine1.28 ± 0.051.34 ± 0.070.56
 NAA/choline1.21 ± 0.021.47 ± 0.090.05
 Choline/creatine1.05 ± 0.040.93 ± 0.030.01
Frontal cortex
 NAA/creatine1.99 ± 0.351.65 ± 0.080.65
 NAA/choline1.42 ± 0.151.32 ± 0.080.32
 Choline/creatine1.37 ± 0.101.25 ± 0.10.79
Occipital cortex
 NAA/creatine2.21 ± 0.162.18 ± 0.270.65
 NAA/choline2.04 ± 0.242.03 ± 0.220.59
 Choline/creatine1.09 ± 0.061.25 ± 0.100.65
Figure 2.

 Cho/Cr (A), NAA/Cr (B), and NAA/Cho (C) ratios for the cerebellum in individual BAFME patients and healthy controls. Error bars with 95% confidence limits are shown. *p < 0.05.

Correlations between 1H-MRS and clinical variables

No correlation was detected between 1H-MRS values and disease duration (r = 0.13; p = 0.86) or myoclonus severity (based on patients’ UMRS scores) (r = 0.12; p = 0.82) (data not shown). In addition, we did not found a correlation between the ratios of metabolites and the antiepileptic therapy (r = 0.34; p = 0.38) (data not shown). We could not investigate the influence of tonic–clonic seizures on 1H-MRS values in those patients who experienced major seizures as these were controlled for several years.

Discussion

The neurochemical abnormalities underlying myoclonic epilepsies are not yet fully defined, and this is a field of active research in both affected humans and animal models (Duncan, 1996; Kuzniecky, 2004; Hiremath & Najm, 2007). 1H-MRS studies showed frontal lobe metabolite abnormalities in patients with juvenile myoclonic epilepsy, a common form of idiopathic generalized epilepsy (Savic et al., 2000, 2004; Simister et al., 2003). Few MRI studies, including both 1H-MRS and morphometry approaches, are available in progressive forms of myoclonic epilepsies such as Unverricht-Lundborg disease (Mascalchi et al., 2002), in which involvement of the brainstem is predominates, and Lafora disease, in which cortical and cerebellar dysfunction has been suggested (Villanueva et al., 2006).

We investigated by 1H-MRS 11 patients with BAFME, an inherited form of myoclonic epilepsy, from three families showing linkage to 2p11.1-q12.2 and sharing a common haplotype. Thus far, the pathophysiologic basis of this condition remains poorly understood. There are no evident underlying structural brain abnormalities on MRI studies (Ikeda et al., 1990; Striano et al., 2005; Uyama et al., 2005) and few neuropathologic data are available (van Rootselaar et al., 2004, 2007a; Uyama et al., 2005). This first study on neurochemical changes in BAFME showed an abnormal increase of the cerebellar Cho/Cr ratio in the patients compared with healthy controls, whereas there was no difference in the metabolite ratios in the frontal and occipital cortex. Although the effects of anticonvulsants on 1H-MRS metabolites have not been thoroughly investigated, it is unlikely that therapy was responsible for the higher concentrations of cerebral Cho/Cr in our series as they occurred likewise in patients with and without antiepileptic medication.

Altogether, our neuroimaging data indicate that the cerebellum is the prominent relevant site of neuronal dysfunction in BAFME in accordance with neuropathologic data (van Rootselaar et al., 2004, 2007a; Uyama et al., 2005). Notably, not only pathologic but also functional studies, such as fMRI (van Rootselaar et al., 2007b) and eye movement abnormalities (Bour et al., 2008), point toward cerebellar dysfunction in this condition.

The abnormal Cho concentrations could reflect gliosis or, more probably, changes in the chemical and functional nature of cell membranes (Duncan, 1996; Savic et al., 2004; Kuzniecky, 2004; Hiremath & Najm, 2007). Accumulating molecular and electrophysiologic data suggest altered cholinergic function in some models of seizure generation (Friedman et al., 2007), and 1H-MRS findings of increased Cho have been observed in rats in which seizures were induced by epileptogenic treatment, probably reflecting an increase in acetylcholine and phospholipids (Jope & Gu, 1991; Kish et al., 1998). Although a mild reduction in NAA/Cr levels was observed, neuronal loss could be too mild to significantly reduce this ratio that, however, was overall lower in the patients compared with controls. Therefore, increased Cho/Cr and unchanged NAA/Cr ratios could reflect mild neuronal loss with consequent gliosis. However, the present data do not allow further speculations about the cause–effect relationship.

In our series, we did not observe correlation between disease duration and severity. However, notably, 1H-MRS changes were observed also in patients with recent onset of the symptoms. Therefore, it is likely that 1H-MRS may facilitate the early identification of patients before the onset of the symptoms in BAFME.

The evidence of cerebellar neuronal metabolic dysfunction in BAFME supports the view that abnormal cerebellar circuitry is the underlying substrate of this condition (Ikeda et al., 1990; Striano et al., 2005; Uyama et al., 2005). This is in line with the known cerebellar pathology described in this condition (van Rootselaar et al., 2004, 2007a; Uyama et al., 2005). A strong relationship between myoclonus and the cerebellum is supported by animal as well as by human studies. In the mouse model of Unverricht-Lundborg disease, a progressive form of myoclonic epilepsy, the principal cytopathology is found in the cerebellum (Pennacchio et al., 1998). In addition, in humans, the pathologic findings associated with cortical myoclonus commonly involve the cerebellar system (Bhatia et al., 1995). In celiac patients with cortical myoclonus, pathologic abnormalities are located mainly in the cerebellum, despite clear electrophysiologic evidence of cortical dysfunction (Bhatia et al., 1995; Tijssen et al., 2000). These data suggest that enhanced excitability of the sensorimotor cortex may arise as a distant effect of cerebellar pathology, likely through the dentate nucleus projections to bilateral motor, premotor, and frontal association cortices via the ventrolateral nuclei of the thalamus (Brown & Marsden, 1996). The identification of BAFME causative mutations probably requires an extensive and collaborative screening effort. When the causative genes are identified, it would be worthy to test whether their pattern of expression is significantly altered in the cerebellum. These data might potentially provide new relevant insights into the pathogenesis of myoclonic epilepsies.

This study has some limitations. In particular, because a single-voxel 1H-MRS was used, no information is available about the spatial extension or homogeneity of the metabolite alterations in our patients. Another consequence of single-voxel acquisition is the variation of the proportion of white and gray matter in the individual VOIs.

Neuroimaging techniques have currently advanced the diagnosis, management, and understanding of the pathophysiology epilepsies. Although it has been traditionally held that there is no radiologic abnormality in patients with idiopathic epilepsies, sophisticated image processing suggest that subtle structural or metabolic abnormalities may contribute to their pathophysiology, apparently making seamless the transition between the poles of idiopathic and symptomatic epilepsy (Duncan, 1996; Kuzniecky, 2004; Hiremath & Najm, 2007). In this study, we showed 1H-MRS reliability for detecting brain changes in BAFME and suggest its role as a useful adjunctive tool supporting this diagnosis based on familial and electrophysiologic data. In the future, other innovative MRI approaches (e.g., volumetry and voxel-based morphometry) should be also considered for specifically designed studies of this intriguing condition.

Acknowledgments

The authors thank the patients and control subjects for participating in the study. We are also grateful to the radiology technician Edoardo Portelli for 1H-MRS data collection and acquisition.

Conflicts of interest: We confirm that we have read the Journal’s position on issues involved in ethical publication and affirm that this report is consistent with those guidelines. The authors have no conflicts of interest to declare.

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