Intermittent Rhythmic Delta Activity Research Articles

Dynamics underlying rhythmic and non-rhythmic variants of abnormal, waking delta activity

Object: We applied a new test, nonlinear cross prediction (NLCP), to investigate whether or polymorphic delta activity (PDA) and frontal intermittent rhythmic delta activity (FIRDA) reflect linear or nonlinear brain dynamics. Furthermore realistic models were constructed to explain the dynamical properties of PDA and FIRDA. Methods: Forty-nine EEG time series with FIRDA and 40 time series with PDA were studied with the NLCP algorithm. This characterizes a time series in terms of its predictability, amplitude asymmetry, and time asymmetry, with the latter two measures reflecting nonlinearity. Parameters of an EEG model proposed by Lopes da Silva were adjusted to obtain time series resembling PDA and FIRDA. Results: FIRDA was more predictable than PDA. Most PDA segments could not be distinguished from linearly filtered noise. In contrast, FIRDA activity showed strong evidence of nonlinear dynamics. These dynamical properties of PDA and FIRDA could be reproduced by the Lopes da Silva model. PDA and FIRDA reflect a point attractor and a limit cycle attractor, respectively, perturbed by dynamical noise. Conclusion: Experimental analysis and modeling of the data suggest that PDA and FIRDA reflect fundamentally different types of brain dynamics. While PDA is filtered noise, reflecting low-level, random input to cortical networks, FIRDA may reflect limit-cycle oscillations due to increased excitation.

Intermittent rhythmic delta activity (IRDA) morphology cannot distinguish between focal and diffuse brain disturbances.

IRDA (intermittent rhythmic delta activity) is an abnormal generalized EEG pattern that is not specific to any single etiology and can occur with diffuse or focal cerebral disturbances. To determine whether different electrographic features of IRDA and associated EEG findings can differentiate underlying focal from diffuse brain disturbances, we performed a blind analysis of 58 consecutive EEGs with an IRDA pattern, recorded from 1993 until 1996, in which we evaluated posterior background activity, focal slowing and IRDA characteristics (frequency, distribution, duration, symmetry and abundance). The clinical diagnosis, state of consciousness and CT brain findings were retrieved from the patients' hospital records. There were 58 patients (33 females; mean age, 58+/-21 years). Twelve (21%) had only focal brain lesions, while 46 (79%) had diffuse brain abnormalities, (15 diffuse structural, 19 metabolic abnormalities, 12 postictal). Normal consciousness and focal EEG slowing were more frequent in patients with focal abnormalities, however, this was not statistically significant. Of the patients with focal abnormality, 11 (92%) had normal posterior background activity either bilaterally (n=4) or contralateral to the focal lesion (n=7). Bilaterally normal posterior background activity was observed in about 30% in both groups. Bilaterally abnormal posterior background activity was apparent in one patient (8%) with focal brain lesion and in 31 patients (67%) with diffuse brain abnormalities (P<0.0001). There were no significant differences in IRDA electrographic features between the focal group and the group with diffuse brain disturbances. We conclude that IRDA morphology cannot distinguish between focal and diffuse brain abnormalities.

Migraine with aura as early symptom of neurosyphilis

On the basis of a case report the often difficult classification of migraine with aura and exclusion of symptomatic origin is discussed. In spring 1996 a 34-years old patient started to suffer from attacks of a migraine like headache with focal aura several times a week. While clinical examination was inconspicuous the electroencephalogram showed a general slowing of background activity with intermittent rhythmic delta-activity. NMR was normal. During treatment with flunarizine intensity and frequency of the attacks decreased, but within half a year he developed an increasing psychomotor slowing and cognitive deficit. Now cerebrospinal fluid showed a pleocytosis and highly positive treponema pallidum specific antibody index making the diagnosis of neurosyphilis reliable. Parenteral penicillin caused a delayed normalisation of mental abilities and CSF. Headache, especially with the characteristics of migraine, is one of the most frequent symptoms of neurosyphilis and--if untreated--may be followed by transient ischemic attacks or strokes even month later. To detect this kind of symptomatic headache a careful neurological follow-up examination and early CSF-analysis are essentially necessary, because pathological electroencephalograms are not rare in migraine with aura and NMR cannot exclude an inflammatory process.

Significance of interictal temporal lobe delta activity for localization of the primary epileptogenic region.

Because interictal temporal lobe delta activity (TLDA) has been described in 30 to 90% of patients with temporal lobe epilepsy (TLE) but has not been investigated in patients with extratemporal epilepsy, we sought to determine the localizing significance of TLDA. We compared the presurgical interictal scalp EEG results of 47 consecutive patients who received extratemporal resection (40 frontal and 7 parietal-occipital) for intractable epilepsy with 43 consecutive patients who received anterior temporal lobectomy. We defined lateralized TLDA as runs of lower than 4-Hz waveforms that were easily distinguished from the background rhythms and were maximal at electrodes T4, F8, and T6 or T3, F7, and T5. The lateralized TLDA was subcategorized as temporal intermittent rhythmic delta activity (TIRDA) or temporal intermittent polymorphic delta activity (TIPDA). A chi-square test was used to determine the association of the lobe of the epileptogenic zone with TIRDA and TIPDA. We found TIRDA in 12 (28%) and TIPDA in 8 (19%) patients in the temporal lobe group, and TIRDA in 2 (4%) and TIPDA in 9 (19%) patients in the extratemporal group. TIRDA was strongly associated with TLE (p < 0.003), whereas TIPDA occurred at an equal rate in both groups. Similar to anterior temporal epilepsy, lateralized TIPDA is present in up to 20% of patients with extratemporal epilepsy. The presence of TIRDA strongly suggests TLE but may infrequently occur in extratemporal epilepsy. Caution should be used when using lateralized TLDA as a presurgical localizing finding.

101 Mathematical characterisation of the dynamics underlying rhythmic and non-rhythmic variants of delta activity

Object: We applied a new test, nonlinear cross prediction (NLCP), to investigate whether or polymorphic delta activity (PDA) and frontal intermittent rhythmic delta activity (FIRDA) reflect linear or nonlinear brain dynamics. Furthermore realistic models were constructed to explain the dynamical properties of PDA and FIRDA. Methods: Forty-nine EEG time series with FIRDA and 40 time series with PDA were studied with the NLCP algorithm. This characterizes a time series in terms of its predictability, amplitude asymmetry, and time asymmetry, with the latter two measures reflecting nonlinearity. Parameters of an EEG model proposed by Lopes da Silva were adjusted to obtain time series resembling PDA and FIRDA. Results: FIRDA was more predictable than PDA. Most PDA segments could not be distinguished from linearly filtered noise. In contrast, FIRDA activity showed strong evidence of nonlinear dynamics. These dynamical properties of PDA and FIRDA could be reproduced by the Lopes da Silva model. PDA and FIRDA reflect a point attractor and a limit cycle attractor, respectively, perturbed by dynamical noise. Conclusion: Experimental analysis and modeling of the data suggest that PDA and FIRDA reflect fundamentally different types of brain dynamics. While PDA is filtered noise, reflecting low-level, random input to cortical networks, FIRDA may reflect limit-cycle oscillations due to increased excitation.

EEG changes in tuberculous meningitis: a clinicoradiological correlation

Objectives: The present study is aimed at describing electroencephalographic (EEG) changes in the tubercular meningitis (TBM) and correlating these with clinical and radiological findings. Methods: All the patients underwent a detailed neurological evaluation, CSF analysis, EEG and CT scan studies. Outcome was assessed by the Barthel index (BI) score at the end of 3 months, into good (BI≥12) and poor (BI<12). Thirty-two patients with TBM have been included of which 3 were definite and the remaining highly probable. Their mean age was 28 (range 8–62) years and 8 of whom were females. The majority of these patients were in stage III. Results: Clinical signs of raised intracranial tension were present in 9 and history of seizure in 11 patients. Cranial CT scan was abnormal in 22 patients. The CT scan abnormalities included hydrocephalus in 20, infarction in 11, exudates in 7 and tuberculoma in 4 patients. The EEG was abnormal in 24 patients. The EEG abnormalities included diffuse theta to delta slowing in 22 patients, intermittent rhythmic delta activity in frontal region in 15, right to left asymmetry in 5 and epileptiform discharges in 4 patients. At the end of 3 months, 5 patients died, 13 had poor, 3 partial and 11 complete recovery. The EEG findings correlated with the severity of meningitis, the degree of coma and outcome at 3 months as assessed by Barthel index score.

Periodic fever associated with intermittent rhythmic delta activity: a syndrome of hypothalamic origin?

We report the case of a patient with a 16 year history of periodic (30 day cycle) fever attacks. The infradian cycle, associated clinical features, and the findings of electroencephalogram recorded during two fever attacks suggest a periodic hypothalamic syndrome.

EEG findings in acetazolamide-responsive hereditary paroxysmal ataxia

EEG studies were performed in six family members affected by acetazolamide-responsive paroxysmal ataxia. Intermittent rhythmic delta activity was found at rest in five of them; low amplitude spikes were associated with delta waves in two cases, resulting in irregular spike and wave patterns. Slowing of background activity was present in three patients. EEG abnormalities were activated by hyperventilation and modified neither by intermittent photic stimulation, nor by acetazolamide therapy. Our results suggest that EEG may be helpful to recognize this rare, but well defined, treatable disorder.

Multiresolution decomposition of non-stationary eeg signals: A preliminary study

Wavelet representation is a recent development in the analysis of non-stationary signals. Its possibilities for use in the description of time-frequency characteristics of both transients in spontaneous EEG and time-varying rhythms in event related brain activity are explored here. By way of illustration, multiresolution decompositions of a wide variety of EEG transients are carried out in this work, including spike-and-waves, single spikes, sharp waves, blink artifacts, frontal intermittent rhythmic delta activity (FIRDA) and paroxysmal delta activity. Also, the application of the wavelet representation to study event related spectra perturbations is illustrated with data from psychophysical experiments on the perception of image motion. The results demonstrate the capabilities of the wavelet transform, as an alternative to the Fourier transform, for the representation and analysis of non-stationary EEG signals.

Hippocampal temporal intermittent rhythmic delta activity (TIRDA) and positive sharp waves during intraoperative EEG recordings suggest another focus distant from a parieto-occipital lesion

Hippocampal temporal intermittent rhythmic delta activity (TIRDA) and positive sharp waves during intraoperative EEG recordings suggest another focus distant from a parieto-occipital lesion

Temporal intermittent rhythmic delta activity in electroencephalograms.

Temporal intermittent rhythmic delta activity (TIRDA) has been reported to be highly specific for diagnosing complex partial epilepsy. Of 12,198 electroencephalographic (EEG) recordings performed at the Mayo Clinic between May 1, 1990 and May 1, 1991, 33 records from 27 patients (18 women and nine men; mean age, 41.5 years; range, 13-82 years) showed TIRDA. Clinical seizures were diagnosed in all patients, and complex partial epilepsy was well documented in 23. In a control group of 100 patients without TIRDA and matched for age and sex, generalized seizures were diagnosed in 25 and partial seizures in 15. Differences between TIRDA and control groups were highly statistically significant. Focal temporal sharp waves or spikes occurred in 23 patients with EEG recordings that contained TIRDA; three of these patients also exhibited generalized atypical spike-and-wave discharges. Four patients had TIRDA but no other epileptiform activity, although earlier EEGs of three of these patients contained spikes or sharp waves. These findings confirm earlier work, and we conclude that TIRDA represents an important epileptogenic abnormality.

Clinical Significance of Diffuse Delta EEG Activity in Chronic Schizophrenia

1) Forty-three chronic schizophrenics with diffuse delta activity (DDA) in their rest-awake EEGs were compared with 23 chronic schizophrenics with normal EEGs. 2) The DDA group was divided into three sub-groups according to the temporal persistence of DDA: brief, intermittent, and prolonged. The intermittent DDA is analogous to intermittent rhythmic delta activity (IRDA). 3) The disorganized type of schizophrenia was frequent in the DDA group and the residual type was frequent in the normal EEG group. 4) The doses of neuroleptics, as well as those of phenothiazines and butyrophenones, were higher in the DDA than in the normal group. 5) The frequency of co-administration of carbamazepine was higher in the DDA than in the normal group, and the rate increased with the degree of abnormality. 6) In a 1 year follow-up of the DDA group, reducing doses of neuroleptics resulted in a tendency for DDA to disappear, and reducing the doses of adjunctive carbamazepine caused DDA to disappear. 7) There was no correlation between DDA and the psychiatric symptoms, intelligence level, or CT findings.

The epileptiform significance of intermittent rhythmic delta activity in childhood.

Intermittent rhythmic delta activity is reported in various disorders and is classified as a nonspecific abnormal electroencephalographic pattern. We have investigated its clinical and electroencephalographic features in childhood. Intermittent rhythmic delta activity was identified in 54 children over a period of 48 months. Epilepsy was present in 81%, 4% had only a single generalized tonic-clonic seizure, and 15% had no seizures. Generalized seizures were more common than partial seizures (83% versus 13%; 4% were mixed). The largest group of patients had idiopathic epilepsy. Epileptiform features were present in 70%. No patient identified prospectively has had a space-occupying lesion. Intermittent rhythmic delta activity should be considered an epileptiform pattern in children, most commonly occurring as an interictal pattern in primary generalized epilepsy.

Temporal intermittent rhythmic delta activity (TIRDA) in the diagnosis of complex partial epilepsy: sensitivity, specificity and predictive value.

Temporal interictal rhythmic delta activity or TIRDA was found in 45 of the 127 recordings of patients with complex partial epilepsy (CPE) referred for both awake and sleep EEG. TIRDA was more abundant during drowsiness and light sleep; it occurred more characteristically as trains of 50-100 microv sinusoidal or saw-toothed 1-4Hz activity, recorded predominantly from anterior temporal regions. When occurring bilaterally and independently, TIRDA varied from side to side. TIRDA is often found in association with anterior temporal spikes or sharp waves (TS) particularly during sleep, as observed in 43 out of 45 EEGs. TIRDA can nevertheless occur as an isolated abnormality, as noted in two sleep and 12 awake study recordings. Because of its high specificity and positive predictive value over a large range of prevalence, TIRDA should be singled out as an accurate interictal indicator of CPE. In patients with isolated TIRDA, the cost of prolonged EEG recording during sleep for the purpose of activating TS has to be weighed against the yield of eventually confirming the obvious.

The electroencephalogram and mental activation.

The mental activation (MA) is a simple test consisting of two questions and two commands given during the waking record. The responses are documented by + or - sign notations made by the technologist. In this manner, data were rapidly obtained from 1280 patients; there were 598 patients with EEG records within normal limits and 682 with various degrees of EEG abnormality. The MA serves the following purposes: a. to study the repercussions of the test on the EEG activity, b. to ascertain the optimal level of vigilance, c. to attempt a correlation of MA responses and the degree of EEG abnormality and d. to obtain brief information on the patient's mental state. The test is administered during conventional EEG recordings. It was found that alpha blocking or attenuation was the exception rather than the rule during the test. Diffuse and focal slowing also remained unchanged in the vast majority of the cases, whereas focal intermittent rhythmical delta activity (FIRDA) was blocked or reduced in most patients exhibiting this pattern. Epileptic conditions were also studied and it was found that, in a single observation, even the most difficult part of the test (item D: mental arithmetic) could be carried out during ictal-subclinical regional EEG activity.

EEG dysfunction in geropsychiatry

Electro-clinical correlations are reported in 200 elderly patients admitted to a psychiatric ward of a general hospital. Normal EEG characteristics were generally associated with functional psychiatric disorder. Abnormal EEG features correlated with organic brain syndromes (O.B.S.). The diagnostic and pathogenetic considerations and restrictions of EEG foci, intermittent rhythmic delta activity (Irda) and diffuse EEG slowing are discussed. The informative value of EEG dysfunction in geropsychiatry is emphasised.

Electroencephalograms in patients with progressive dialytic encephalopathy.

We compared the electroencephalograms (EEGs) of 17 patients with progressive dialytic encephalopathy with 17 chronic renal failure patients who did not have dialytic encephalopathy and who had been matched for age, type and duration of dialysis. The EEGs were analyzed in a semiquantitative fashion by counting the number of paroxysms of frontal intermittent rhythmic delta activity and frontocentral spike-waves, and by grading the amount of diffuse theta and delta waves during waking EEG on a 4-point scale. The two most important EEG predictors of dialytic encephalopathy in the present study consisted of synchronous and symmetrical frontal intermittent rhythmic delta waves and frontocentral spike-waves, confirming our previous observations.

Frontal intermittent rhythmic delta activity. A comparative study of EEG and CT scan findings.

26 cases with frontal intermittent rhythmic delta activity (FIRDA) in the EEG are presented and compared to the corresponding results in computerized axial tomography (CT) of the brain. Selection was undertaken randomly without reference to special diagnostic aspects. Only 3 cases showed a deviation of the cerebral midline structures in the CT, because of a cerebral tumor. No deviation of the midline structures in the CT could be found in the other 23 cases, where FIRDA was the outstanding finding in the EEG. Thus, the conclusion may be drawn that FIRDA in the EEG is by no means indicative of subcortical lesions, especially tumors, with alteration of midline structures.

Relationship of pre- and postanesthetic EEG abnormalities to enflurane-induced seizure activity.

In 12 subjects, serial electroencephalograms (EEGs) following a standard exposure to enflurane anesthesia were evaluated with respect to (1) preanesthetic baseline EEGs, and (2) the occurrence of clinical or electrographic epileptiform EEG activity during anesthesia. There were no consistent predictors of enflurane-induced seizure activity in the preanesthetic EEG recordings, although the one patient of the group with a marginal preanesthetic EEG abnormality manifested the largest number of seizures during anesthesia (but none subsequently). No specific relationship was found between the duration of postanesthetic EEG changes and the occurrence of a seizure during anesthesia. Postanesthetic EEGs from all subjects showed diffuse slowing. Three specific electrographic alterations were also found: (1) In all 12 subjects, the alpha frequency decreased by 1 to 4 Hz for 2 to 6 days after anesthesia. (2) In 8 subjects, posterior intermittent rhythmic delta activity persisted for 6 to more than 30 days after enflurane. (3) An increased amplitude and incidence of benign incidental preanesthetic focal EEG findings seen in 6 subjects could be demonstrated for 2 to 30 days after anesthesia. In general, EEG changes were seen for 6 to 30 days after anesthesia, but at no point did de-novo EEG epileptiform activity appear in any subject following anesthesia.