Fixation-sensitive myoclonus in Lafora disease

Case Report: Distinctive EEG Patterns in SCARB-2 Related Progressive Myoclonus Epilepsy

Action myoclonus-renal failure syndrome (AMRF) is a rare, recessively inherited form of progressive myoclonus epilepsy (PME) caused by mutations in the SCARB2 gene and associated with end-stage renal failure. In addition to severe progressive myoclonus, the neurological manifestations of this syndrome are characterized by progressive ataxia and dysarthria with preserved intellectual capacity. Since its original description, an increasing number of "AMRF-like" cases without renal failure have been reported. We describe the case of a 29-year-old woman with progressive disabling myoclonus associated with dysarthria and ataxia who was found to have a novel homozygous frameshift mutation in the SCARB2 gene. In addition, this report emphasizes the presence of two EEG patterns, fixation-off phenomenon, and bursts of parasagittal spikes exclusively seen during REM sleep that appear to be characteristic of this condition.

Structural and Functional Brain Abnormalities in Mouse Models of Lafora Disease

Mutations in the EPM2A and EPM2B genes, encoding laforin and malin proteins respectively, are responsible for Lafora disease, a fatal form of progressive myoclonus epilepsy with autosomal recessive inheritance. Neuroimaging studies of patients with Lafora disease have shown different degrees of brain atrophy, decreased glucose brain uptake and alterations on different brain metabolites mainly in the frontal cortex, basal ganglia and cerebellum. Mice deficient for laforin and malin present many features similar to those observed in patients, including cognitive, motor, histological and epileptic hallmarks. We describe the neuroimaging features found in two mouse models of Lafora disease. We found altered volumetric values in the cerebral cortex, hippocampus, basal ganglia and cerebellum using magnetic resonance imaging (MRI). Positron emission tomography (PET) of the cerebral cortex, hippocampus and cerebellum of Epm2a^-/- mice revealed abnormal glucose uptake, although no alterations in Epm2b^-/- mice were observed. Magnetic resonance spectroscopy (MRS) revealed significant changes in the concentration of several brain metabolites, including N-acetylaspartate (NAA), in agreement with previously described findings in patients. These data may provide new insights into disease mechanisms that may be of value for developing new biomarkers for diagnosis, prevention and treatment of Lafora disease using animal models.

Update on Pharmacological Treatment of Progressive Myoclonus Epilepsies

BACKGROUND

Progressive myoclonus epilepsies (PMEs) are a group of rare inherited diseases featuring a combination of myoclonus, seizures and variable degree of cognitive impairment. Despite extensive investigations, a large number of PMEs remain undiagnosed. In this review, we focus on the current pharmacological approach to PMEs.

METHODS

References were mainly identified through PubMed search until February 2017 and backtracking of references in pertinent studies.

RESULTS

The majority of available data on the efficacy of antiepileptic medications in PMEs are primarily anecdotal or observational, based on individual responses in small series. Valproic acid is the drug of choice, except for PMEs due to mitochondrial diseases. Levetiracetam and clonazepam should be considered as the first add-on treatment. Zonisamide and perampanel represent promising alternatives. Phenobarbital and primidone should be reserved to patients with resistant disabling myoclonus or seizures. Lamotrigine should be used with caution due to its unpredictable effect on myoclonus. Avoidance of drugs known to aggravate myoclonus and seizures, such as carbamazepine and phenytoin, is paramount. Psychiatric (in particular depression) and other comorbidities need to be adequately managed. Although a 3- to 4-drug regimen is often necessary to control seizures and myoclonus, particular care should be paid to avoid excessive pharmacological load and neurotoxic side effects. Target therapy is possible only for a minority of PMEs.

CONCLUSIONS

Overall, the treatment of PMEs remains symptomatic (i.e. pharmacological treatment of seizures and myoclonus). Further dissection of the genetic background of the different PMEs might hopefully help in the future with individualised treatment options.

Coexistence of fixation-off sensitivity and inverted fixation-off sensitivity in a female child with Panayiotopoulos syndrome: Video-electroencephalography documentation

Fixation-off sensitivity (FOS) is a rare phenomenon elicited by elimination of central vision and fixation, which even in the presence of light induces occipital paroxysms or generalized paroxysmal discharges. It is most commonly encountered in patients with idiopathic childhood occipital epilepsies but may also be observed in cases of symptomatic focal and generalized epilepsies. We describe a female Emirati child with Panayiotopoulos syndrome who exhibited FOS in addition to the reverse phenomenon called "inverted fixation-off sensitivity," in which the electroencephalographic discharges were suppressed by the absence of central vision or fixation and activated by central vision or fixation.

The uncommon causes of status epilepticus: a systematic review

This paper reports the first systematic review of uncommon causes of status epilepticus reported in the literature between 1990 and 2008. Uncommon causes are defined as those not listed in the main epidemiological studies of status epilepticus. 181 causes were identified. These were easily categorised into 5 specific aetiological categories: immunological disorders, mitochondrial disorders, infectious diseases, genetic disorders and drugs/toxins. A sixth category of 'other causes' has also been included. Knowledge of these causes is important for clinical management and treatment, and also for a better understanding of the pathophysiology of status epilepticus.

Lafora disease: epidemiology, pathophysiology and management

Lafora disease is a rare, fatal, autosomal recessive, progressive myoclonic epilepsy. It may also be considered as a disorder of carbohydrate metabolism because of the formation of polyglucosan inclusion bodies in neural and other tissues due to abnormalities of the proteins laforin or malin. The condition is characterized by epilepsy, myoclonus and dementia. Diagnostic findings on MRI and neurophysiological testing are not definitive and biopsy or genetic studies may be required. Therapy in Lafora disease is currently limited to symptomatic management of the epilepsy, myoclonus and intercurrent complications. With a greater understanding of the pathophysiological processes involved, there is justified hope for future therapies.

Inverted fixation-off sensitivity in atypical benign partial epilepsy

Fixation-off sensitivity is an electroencephalographic phenomenon characterized by spike-and-wave discharges that only occur when central vision and fixation are eliminated. It is especially seen in children with Panayiotopoulos-type, early-onset, benign childhood occipital epilepsy or Gastaut type, late-onset, childhood occipital epilepsy. It can also be seen in eyelid myoclonia with absences, in other idiopathic generalized epilepsies, and in asymptomatic children without epilepsy. We describe a boy with atypical, benign partial epilepsy of childhood who exhibited the reverse: epileptiform activity that was suppressed by the absence of central vision or fixation, and activated by central vision or fixation.