"Mitochondrial myopathy" or mitochondrial disease? EEG, ERG, VEP studies in 13 children

Mitochondrial Disease with Myopathy

Mitochondrial disease with myopathy is a rare progressive disease which affects more than one system of the body. It can be diagnosed only by muscle biopsy showing ragged red fiber cells (RRFs) that requires special (trichrome) staining, often not available in routine histopathology laboratories. There is no specific treatment or cure for the condition. A case, confirmed by biopsy, is reported in a 42-year-old Qatari female suffering from previously undiagnosed chronic progressive weakness and possibly related hyperthyroidism. Muscle weakness, deafness, muscle biopsy Hyperthyroidism

Visually evoked potentials in respiratory chain disorders

OBJECTIVES

Little is known about the frequency of abnormal visually evoked potentials (VEPs) in patients with respiratory chain disorders (RCDs). We thus wanted to investigate the frequency of abnormal VEPs in RCDs, how often VEPs are abnormal despite normal visual acuity, and which of the VEP variables are most often abnormal.

MATERIAL AND METHODS

Reversal checkerboard VEPs of 26 patients with RCDs, aged 32-74 years, were evaluated.

RESULTS

VEPs were abnormal in 17 of the 26 cases (65%). The P100 latency was prolonged at least unilaterally in 16 patients. The P100/N145 amplitude was decreased in a single patient. VEPs were abnormal without visual impairment in 9 cases (53%).

CONCLUSION

VEPs prove useful to detect clinical or subclinical impairment of the optical tract in patients with RCDs. In the majority of the cases, the P100 latencies are prolonged while the P100/N145 amplitude remains normal.

Video-EEG monitoring in respiratory chain disorders

Subclinical epileptiform activity in patients with respiratory chain disorders (RCDs) has not been previously investigated by video-EEG monitoring. The purpose of this study was to look for the type and frequency of epileptiform activity during a 24 h-video-EEG recording in RCD patients. Eleven patients with RCD, 7 women and 4 men, aged 24-72 years, underwent a clinical neurologic examination, blood tests, CT/MRI scans of the brain, routine scalp EEG and continuous video-EEG monitoring over 24 consecutive hours. Ten patients had normal 24 h-video-EEG recordings. One of these patients had no CNS involvement; her resting EEGs showed diffuse background slowing. In one patient, automatic spike detection revealed 12 spikes during a 6 hour period. Resting scalp EEG in this patient showed extensive, bilaterally synchronous, pseudoperiodic polyspike-waves. In conclusion, subclinical epileptiform activity could be recorded by 24 h-video-EEG monitoring in only 1 of 11 RCD patients. The single patient with subclinical epileptiform activity presented with intermittent myoclonic jerks.

Utility of multimodal evoked potential study and electroencephalography in mitochondrial encephalomyopathy

We performed electroencephalography (EEG) and multimodal evoked potential (EP) studies in 16 patients with various forms of mitochondrial encephalomyopathy (ME). The electrophysiological investigations revealed signs of involvement of the peripheral and central nervous system (CNS) in 14 patients, with a high incidence of visual-EP (VEP) alterations, indicative of visual pathway vulnerability in mitochondrial diseases. No specific pattern of abnormalities emerged and, in particular, clinical and laboratory findings did not correlate with each other. EP (particularly VEP and electroretinogram) investigations should be part of the diagnostic work-up of patients with mitochondrial disorders in order to better characterize the clinical picture, disclose involvement of specific sensory systems of the CNS, and assess patients with atypical clinical presentations.

Visual dysfunction in patients with mitochondrial myopathies. I. Electrophysiologic impairments

Seventeen patients with biopsy-confirmed mitochondrial progressive external ophthalmoplegia underwent electroretinography and visual evoked potential testing to checkerboard-reversal stimuli to investigate subclinical visual dysfunction. Seven patients (41%) had impaired Snellen visual acuity that was never less than 0.6. Thirteen patients (76%) showed electroretinographic and/or visual evoked potential alterations, whereas six (35%) showed impairment on both tests. Two patients showed delayed VEP P100 latency without fundus, electroretinographic or visual acuity anomalies. Visual dysfunctions were not related to age at onset and course of the disease.

Evoked potentials in mitochondrial disorders

Twenty-eight adult patients with mitochondrial disease were evaluated with muitimodal evoked potentials (EPs) to assess a possible CNS involvement The patients were classified into five groups: encephalopathy (two cases), progressive external ophthalmoplegia (PEO; four cases), pure myopatby (15 cases), cardiomyopathy (five cases) and asymptomatic relatives (two cases). EPs showed differences between encephalopathy (all EP modalities affected) and PEO groups (all patients with at least one EP altered), with lesser degrees of affection in pure myopathy and cardiomyopathy groups. The asymptomatics registered normal EPs. In view of these results, progressive CNS damage in mitochondriopathies, expressed by abnormal EPs, can be established as follows (from greatest to minor severity): encephalopathy, PEO, pure myopathy/cardiomyopathy and asymptomatic condition.

EEG and evoked potential findings in mitochondrial myopathies

Electroencephalograms (EEGs) and evoked potentials (EPs) were studied in 43 patients with mitochondrial myopathies. Abnormalities were found most frequently in patients who presented predominantly or exclusively with central nervous system (CNS) dysfunction (abnormal EEGs in 18 of 21 patients, abnormal EPs in 9 of 11 patients). However, of patients presenting with ocular myopathy or proximal muscle weakness who had little or no CNS involvement clinically, 8 of 22 had abnormal EEGs and 5 of 10 had abnormal EPs, suggesting that electrophysiological tests are of value in demonstrating subclinical CNS disease in mitochondrial myopathy, although the abnormalities are not specific.

The electroretinogram

The electroretinogram, findings, in response to a flash stimulus, was recorded from a skin electrode placed on the bridge of the nose in 4465 infants and children seen over a 10 year period. The electroretinogram was combined with a flash visual evoked potential. From this total, the electroretinographic findings in 240 patients, aged 1 day to 17 years, without suspected retinal pathology and with a normal visual evoked potential, were used as controls and normal electroretinographic parameters of different age groups defined. There were 332 patients who showed an absent or very reduced amplitude electroretinogram. They were divided into primarily ocular disorders (n = 195), neurodegenerative disorders (n = 94), and various syndromes (n = 43). Fundus examination did not always show any obvious abnormalities. The use of this simple and reliable technique for recording the electroretinogram made it possible to include this investigation as a routine procedure without the need for sedation in infants and uncooperative children. Electroretinographic studies, especially when combined with visual evoked potentials, and in some cases electroencephalography, may aid diagnosis in a wide variety of paediatric conditions, many of which have genetic implications.

Ophthalmoplegia plus, an electro-oculographic study

To find out whether the central structures governing conjugate eye movements are affected in ophthalmoplegia plus (OP), we conducted an electro-oculographic study in 6 patients suffering from OP with varying degrees of extraocular involvement and with mitochondrial changes in the skeletal musculature. All the patients presented alterations of the smooth pursuit and saccadic movements, of optokinetic nystagmus as well as of the vestibular reflexes and of visuovestibular interaction, thus confirming impairment of the central oculomotor structures and particularly of those of the archicerebellum and brainstem. These data suggest a supranuclear component in the pathogenesis of ophthalmoplegia and are in accord with the findings of brainstem spongiosis in OP, which in turn seem to express a multisystem pathological state of the mitochondria.

Maternally inherited mitochondrial myopathy and myoclonic epilepsy

A family is described with familial myoclonic epilepsy associated with mitochondrial myopathy. The disorder follows a maternal inheritance pattern consistent with a mitochondrial DNA (mtDNA) mutation. The large kindred permitted exclusion of autosomal dominant, recessive, and X-linked patterns of transmission. Several characteristics of the inheritance and variability of expression within the pedigree are consistent with recently acquired knowledge about the genetics of human mtDNA. The clinical spectrum of disease is compatible with a proportionality model of mutant and wild-type mtDNAs. Muscle biopsies of affected patients showed an increased number of abnormal muscle mitochondria. Serum levels of pyruvate or pyruvate and lactate were elevated. The most severely affected patient had constant myoclonic jerking, dementia, ataxia, spasticity, hearing loss, and hypoventilation. Cerebral dysfunction in patients with mild involvement was marked by prominent photic driving seen on electroencephalograms and high-amplitude visual and somatosensory evoked responses but no myoclonus, ataxia, or dementia. The individual clinical features of the disease worsen over time for all patients; however, mildly affected patients have not become moderately affected and moderately affected patients have not become severely affected.

Electroencephalographic findings in patients with chronic progressive external ophthalmoplegia

A retrospective study of the electroencephalographic patterns in 26 adults with chronic progressive external ophthalmoplegia. 12 of them presented EEG anomalies, all slight and aspecific. Of the various parameters considered (age, age at onset, duration of disease, CT, CSF findings, abnormalities of muscle mitochondria) the only two that seem to correlate are altered EEG patterns and severity of mitochondrial anomalies in skeletal muscle tissue.