Periodic sharp waves in baclofen-induced encephalopathy

Acute encephalopathy and an abnormal electroencephalogram with a periodic sharp wave pattern developed in a 58-year-old woman shortly after she received a few doses of baclofen. The clinical and electroencephalographic abnormalities improved promptly after the medication was discontinued.     

Hybrid fibrillation potentials and positive sharp waves

Fibrillation potential configurations are characterized as initially positive triphasic waveforms, whereas positive sharp waves appear biphasic with an initial positive deflection. Careful observation of single muscle fiber discharges in denervated muscle, however, can reveal many different-appearing and stable firing waveforms that resemble a bifid positive sharp wave or some form of combined fibrillation potential and positive sharp wave. In this investigation, a number of atypical-appearing single muscle fiber discharges are hypothesized to arise from particular interactions between the muscle fiber and recording electrode. Single muscle fiber potentials are modeled as originating from a single denervated muscle fiber's former endplate and midfiber region as well as from the fiber's tendinous termination for both a compressed and sealed end effect. The modeled waveforms' appearance corresponds well to those obtained clinically and the necessary interpotential summated templates' temporal domains are feasible for action potential termination at the electrode with subsequent reinitiation beyond the proposed peri-electrode compressed region. It is hypothesized that the majority of hybrid waveforms are the result of a single muscle fiber action potential terminating at a recording electrode while also initiating a "skipped" activation of the muscle fiber past the electrode resulting in the summation of two distinct time-locked waveforms.     

Positive temporal sharp waves in neonatal EEG

The clinical correlates and EEG characteristics of rolandic positive sharp waves in neonatal EEG have been studied systematically. Morphologically similar positive sharp waves have been reported to occur in the temporal areas (PTS). Their significance is, however, unclear. We reviewed fifty-two EEGs on patients from the Neonatal Intensive Care Unit of the University of Arkansas for Medical Sciences. Twenty-one of the EEGs which were reviewed had PTS. We correlated the PTS with the results of ultrasound of the head and with clinical evaluations. PTS are more strongly correlated with the occurrence of non-hemorrhagic than of hemorrhagic intracranial pathology.     

Significance of positive temporal sharp waves in the neonatal electroencephalogram.

We reviewed our computerized neonatal EEG database for records judged to display excessive positive temporal sharp waves (PTS) to determine their electroclinical associations and significance. Typical infants with excessive PTS were: (1) mature, with a mean conceptional age of 41.2 weeks, and (2) neurologically ill, judged by their high rate of associated EEG background abnormality (37 of 46; 80%) and clinical signs of encephalopathy (19 of 29; 66%). In comparison, healthy age-matched control infants never had excessive PTS. We consider an excess of PTS to be pathologic since they arise out of an abnormal EEG background in children exposed to potentially serious central nervous system illnesses and are associated with a high incidence of cerebral structural abnormalities (16 of 25; 64%). PTS may be comparable to the positive rolandic or vertex sharp waves in premature infants with periventricular injury of the deep white matter.     

Some observations on fibrillations and positive sharp waves

Electromyographic recordings of fibrillation potentials (FPs) and positive sharp waves (PSWs) demonstrate transformation of FP to PSW and vice versa, atypical firing patterns, changes in waveform shape and amplitude, and time-locked potentials. The etiology of the waveform characteristics of FP and PSW is discussed based on abnormal propagation in a small section of muscle fiber that is "damaged" by the needle. The results of simple computer simulations are described.     

Hippocampal sharp waves: Their origin and significance

This study investigated the spatial distribution and cellular-synaptic generation of hippocampal sharp waves (SPW) in the dorsal hippocampus of the awake rat. Depth analyses of SPWs were performed by stepping the recording electrode in 82.5 microns increments. SPWs were present during slow wave sleep, awake immobility, drinking, grooming and eating (0.01-2/s). The largest negative SPWs were recorded from the middle part of the stratum radiatum of CA1, the stratum lucidum of CA3, the inner molecular layer of the dentate gyrus and from layer I of the subiculum, in that order. The polarity of the SPWs was positive in layers II-IV of the subiculum, in stratum oriens and stratum pyramidale of CA1 and CA3, and in the hilus of the dentate gyrus. The electrical gradients across the null zones of the field SPWs were as large as 8-14 mV/mm. SPWs were associated with population bursts of pyramidal cells and increased discharges of interneurons and granule cells. During the SPW the excitability of granule cells and pyramidal cells to afferent volleys increased considerably. Picrotoxin and atropine and aspiration lesion of the fimbria-fornix increased either the amplitude or the frequency of SPWs. Diazepam and Nembutal could completely abolish SPWs. It is suggested that: hippocampal SPWs are triggered by a population burst of CA3 pyramidal cells as a result of temporary disinhibition from afferent control; and field SPWs represent summed extracellular PSPs of CA1 and subicular pyramidal cells, and dentate granular cells induced by the Schaffer collaterals and the associational fibers of hilar cells, respectively. The relevance of the physiological SPWs to epileptic interictal spikes and long-term potentiation is discussed.     

Triphasic sharp waves in a patient with carcinomatous meningitis

Subacute encephalopathy with an electroencephalographic (EEG) pattern of generalized periodic triphasic sharp waves occurred in an 80-year-old woman with autopsy proven carcinomatous meningitis. Meningeal carcinomatosis should be included within the differential (clinical) diagnosis of such an EEG pattern.     

Positive temporal sharp waves in preterm infants with and without brain ultrasound lesions.

OBJECTIVE: Clinical significance of neonatal positive temporal sharp waves (PTS) is controversial. The aim of this work is to study (1) PTS incidence in preterm infants with or without major ultrasound lesion (MUL) per gestational age (GA), and (2) the relationship between PTS in both sleep states and other electroencephalographic (EEG) findings with poor prognoses. METHODS: 97 preterm infants of <27-36 weeks GA, and 12 full-term healthy infants were presented. Prospective study included (1) neurodevelopmental assessment at 40-42 weeks conceptional age (CA), (2) serial neurosonography, and (3) EEG recording at postnatal week 1, 2, 4 and at 40-42 weeks CA. RESULTS: In 50 neonates without MUL, peak PTS was at 31-32 weeks GA. In 47 neonates with MUL, PTS increased significantly from week 2 after birth, descending at the 4th. Neonates of <33 weeks GA with MUL showed significantly increased PTS at term. A significant relationship was found between PTS and other EEG abnormalities with poor neurologic prognoses. PTS incidence varied with sleep states, being predominant in indeterminate sleep in neonates with MUL. CONCLUSIONS: PTS increased significantly in infants with MUL, mainly at week 2 of postnatal life, persisting high until term CA, and correlated with other abnormal EEG findings. SIGNIFICANCE: PTS are highly sensitive to MUL.     

The difference between fibrillations and positive sharp waves is due to tissue filtering.

Fibrillation potentials and positive sharp waves share many characteristics, and in general have the same clinical importance. Whether they are two species of the same potential or two different waveforms has been a long-standing controversy. The blocking hypothesis and inadvertent intracellular recording are two theories proposed to explain the difference between the two potentials, but neither is entirely satisfactory. In this study, waveforms with fibrillation potential configurations are modified by the standard filter settings on an electromyograph to attain positive sharp wave configurations. Single-fiber muscle action potentials were recorded at a low-frequency filter of 500 Hz and a high-frequency filter of 20 kHz, and had the appearance of a fibrillation potential. Changing the low-frequency filter and high-frequency filter to 0.2 Hz and 100 Hz respectively caused these same potentials to have a positive sharp wave configuration. Similarly, fibrillation potentials recorded from patients at a low-frequency filter and a high-frequency filter of 20 Hz and 10 kHz respectively had the appearance of positive sharp waves when the low-frequency filter and high-frequency filter were changed to 0.2 Hz and 500 Hz respectively. The authors propose that tissue filtering and the spatial relationship of the fibrillating fiber to the recording electrode determine whether the waveform will have a fibrillation potential configuration or a positive sharp wave configuration. The ability to model these waveforms artificially simply by changing the bandpass suggests that the passive electrical properties of the recording environment may suffice to explain much of the difference between fibrillation potentials and positive sharp waves.     

Occipital sharp waves in idiopathic partial epilepsies--clinical and genetic aspects

In order to gain new insight into the pathogenesis and nosography of benign partial epilepsy with occipital paroxysms (BEOP) we retrospectively analysed cases with benign focal sharp waves (SHW) of different localisations, in which analogous EEG changes had been found in at least one first degree relative. Fifty-six families were evaluated. Nineteen cases with occipital SHW (group A) were compared with 37 cases without (group B). There was a broad spectrum of symptomatology with large overlaps between the two groups. However, a number of striking differences, yielding a characteristic picture of early childhood epilepsy with occipital foci were identified: (1) Age of onset under 5 years; (2) a larger proportion of febrile convulsions (FC 47 vs. 19%); (3) a trend towards a higher rate of typical early childhood occipital seizures (26 vs. 5%); (4) a higher rate of frontal and generalizing SHW foci (32 vs. 5%; 37 vs. 11%); (5) a higher rate of generalized spikes and waves (SW) (46 vs. 14%); (6) a trend towards a higher rate of photoparoxysmal response (PPR) (57 vs. 32%). The high prevalence of independent genetic traits favours a multifactorial pathogenesis. The predisposition to FC with characteristic early seizure onset and varying patterns of generalized genetic EEG traits plays a crucial role within the complex pathogenetic network. The early-onset benign childhood occipital seizure susceptibility syndrome of Panayiotopoulos (Benign Childhood Partial Seizures and Related Epileptic Syndromes, John Libbey & Company Ltd., London (1999)) cannot be regarded as the sole representative of occipital spikes in early childhood but as an important even though rare form of occipital epilepsy.     

Positive rolandic sharp waves and periventricular leukomalacia in the newborn

Four cases of periventricular ischemia without hemorrhage in premature infants are described in which positive rolandic sharp waves (PRSW) were predominant in the electroencephalogram (EEG). These findings suggest the relationship of PRSW to periventricular ischemia rather than to intraventricular hemorrhage, per se, as has been considered by most investigations in the past. These PRSW can provide an early indication of periventricular leukomalacia.     

Positive sharp waves in the EEG of children and adults

Interictal epileptiform discharges (IEDs) with negative polarity have been extensively studied in the EEG literature. However, little attention has been drawn to IED with positive polarity [positive sharp waves (PSWs)]. In this paper, we discuss pathophysiological, neuroimaging, and clinical correlates of this pattern in a heterogeneous group of children and adults who demonstrated PSW in their scalp EEG. We prospectively reviewed the EEGs of 1,250 patients from a heterogeneous population over a period of 1 year. Thirty-one patients had PSW in their EEG. We documented EEG parameters as well as demographic, clinical, and neuroimaging data. Statistical analysis was performed to correlate the aforementioned data. The analysis showed that PSW is an epileptogenic pattern with localizing significance, occurring primarily in the younger age groups. Furthermore, there was a strong association of PSW with chronic and/or static CNS pathology, in particular, congenital CNS anomalies, often accompanied by psychomotor retardation. Patients with “multifocal’’ PSW invariably exhibited severe intellectual and motor deficits associated consistently with a variety of congenital CNS insults. PSW is a rare and under-reported EEG abnormality which, similar to negative IED, signifies focal epileptogenecity. The presence of PSW should prompt neuroimaging studies to investigate an associated chronic/static CNS pathology, in particular, congenital CNS anomalies. This association is particularly strong when PSW is multifocal in which case patients present with severe intellectual and motor deficits.     

Adenosine as an endogenous regulating factor of hippocampal sharp waves

The rodent hippocampus exhibits population activities called sharp waves (SPWs) during slow wave sleep and wake immobility. SPWs are important for hippocampal-cortical communication and memory consolidation, and abnormal sharp wave-ripple complexes are closely related to epileptic seizures. Although the SPWs are known to arise from the CA3 circuit, the local mechanisms underlying their generation are not fully understood. We hypothesize that endogenous adenosine is a local regulator of hippocampal SPWs. We tested this hypothesis in thick mouse hippocampal slices that encompass a relatively large hippocampal circuit and have a high propensity of generating spontaneous in vitro SPWs. We found that application of adenosine A1 receptor antagonists induced in vitro SPWs and that such induction was sensitive to blockade by NMDA receptor antagonists. By contrast, an increase in endogenous adenosine via pharmacological inhibition of adenosine transporters or adenosine degrading enzymes suppressed spontaneous in vitro SPWs. We thus suggest that the initiation and incidence of sharp wave-like population events are under tight control by the activity of endogenously stimulated A1 receptors.     

The relationship between slow and sharp waves (spikes) and also clinical seizures.

This study investigated the relationship between slow waves and sharp waves (spikes) and also clinical seizures in 255 patients with 694 EEGs over a 25-yr period. Slow waves were quantified into five groups, sharp waves into three groups and clinical seizures also into three groups. In general, as clinical seizures increased, the number of patients with many discharges increased and the number with only rare discharges decreased. Also, as patients became seizure free, there was a decreasing incidence of many sharp waves and an increasing incidence of only rare sharp waves. No relationships could be found in patients with a typical number of discharges or a steady number of seizures. Thus, a relationship between sharp waves and seizures was found mainly when there were changes in these variables. For sharp and slow waves, rare discharges were most often associated with mild slowing, while many discharges were most often related to a marked degree of slow wave abnormality. The combination of slow and sharp waves together, compared with only one type of EEG abnormality, was associated with more clinical neurological symptoms, especially a mental status change. The EEG groups were divided into four types of findings of slow and sharp waves, appearing in at least a first and/or second record. The results from these four EEG groups allow for a prediction of the findings to be found in a second record, based on the results of the first EEG. In general, there was a relationship between more slow waves, more sharp waves and more seizures. Also minimal slowing and rare discharges on the first record tended to disappear in the next EEG.     

Positive rolandic sharp waves in neonatal EEG; types and significance

We describe two types of electropositive rolandic sharp waves (PRS) in EEGs of premature infants with markedly different prognostic implications. Type A occurs singly and is clearly distinguished from the background activity; type B appears in bursts and blends somewhat with the background. Among neonates recorded at less than 35 weeks' conceptional age, 21% of those with type A only had normal neurological examinations or only minor sequelae at age 2 years. When type B appeared in the same tracing as type A, the percentage with normal examinations or minor sequelae at 2 years rose to 86%. Only 42% of those without type A or B had favourable 2 year evaluations. For those recorded at 35 weeks or later, normal or minor sequelae were found at 2 years as follows: type A only - 57%; type B only - 75%; types A and B - 92%; no positive rolandic sharp waves - 53%. We conclude that in both age groups type B PRS confer a relatively favourable prognosis and are more prognostically influential than type A. Patients with either type A or no PRS have less favourable outcomes than those with type B. Finally, although the majority of patients with intraventricular haemorrhage have type A PRS, IVH occurred in only 50% of patients with type A PRS when recorded before 35 weeks' conceptional age.     

Transitional sharp waves at ictal onset – A neocortical ictal pattern

ObjectiveSome seizures are characterized by a transitional sharp wave (TShW) at ictal onset. We evaluated the clinical significance and localizing value of TShW in partial-onset seizures.MethodsWe identified and analyzed all scalp ictal recordings with a TShW at ictal onset in the Vanderbilt Epilepsy Monitoring Unit over a period of 12 months.ResultsA total of 52 ictal discharges in 13 patients started with a TShW. The center of TShW field was concordant with the final localization/lateralization, while that of the subsequent ictal discharge was concordant in only 6 patients. The subsequent rhythmic ictal discharge was non-localizing in 4 patients and misleading in the remaining 3 patients. The final localization was neocortical temporal or frontal in 11 patients, occipito-parietal in one, and undetermined in 1 patient. None of 61 ictal discharges in 15 patients with mesial temporal lobe epilepsy studied in the same time period started with a TShW.ConclusionIn this patient series, the TShW was a marker of neocortical seizure onset. The TShW field provided more accurate localization or lateralization of the ictal focus than the following rhythmic ictal discharge.SignificanceTShW at seizure onset should suggest a neocortical rather than hippocampal seizure onset.