Intermittent rhythmic delta activity patterns

Epilepsy & Behavior 20 (2011) 254–256

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Epilepsy & Behavior j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / ye b e h

Review Article

Intermittent rhythmic delta activity patterns Francesco Brigo ⁎ Department of Neurological, Neuropsychological, Morphological and Movement Sciences, Section of Neurology, University of Verona, Verona, Italy Policlinico G. Rossi, Verona, Italy

a r t i c l e

i n f o

Article history: Received 3 November 2010 Revised 15 November 2010 Accepted 15 November 2010 Available online 26 January 2011 Keywords: Intermittent rhythmic delta activity FIRDA OIRDA TIRDA

a b s t r a c t Intermittent rhythmic delta activity is a typical EEG pattern that was originally described by W.A. Cobb in 1945 (J Neurol Neurosurg Psychiatr 1945;8:65–78). It may be classified into three distinct forms according to the main cortical region involved on the EEG: frontal (FIRDA), temporal (TIRDA), and occipital (OIRDA) intermittent delta activity. This article is a review of the main aspects of these patterns, with a special focus on EEG features and problems that may be encountered during interpretation of these patterns. In contrast to FIRDA and OIRDA, TIRDA is highly indicative of ipsilateral pathology. OIRDA and TIRDA are highly correlated with epilepsy, whereas FIRDA is a rather nonspecific EEG pattern. © 2010 Elsevier Inc. All rights reserved.

1. Introduction Intermittent rhythmic delta activity is a typical EEG pattern originally described by Cobb in 1945 [1]. It may be classified into three distinct forms based on the main cortical region involved on the EEG: frontal (FIRDA), temporal (TIRDA), and occipital (OIRDA) intermittent delta activity. This article reviews the main aspects of these patterns, with a special focus on EEG features and problems that may be encountered during their interpretation (Fig. 1). 2. Frontal intermittent rhythmic delta activity Intermittent rhythmic delta activity prevalent over frontal regions is known as FIRDA. FIRDA was initially described by Cobb in 1945 [1], although the term was coined by van der Drift and Magnus in 1959 [2]. This activity is characterized by transient intermittent rhythmic slow waves with a frequency of 1.5 to 4.0 Hz localized mainly over frontopolar regions [3]. In contrast to OIRDA, FIRDA occurs in adulthood. This typical EEG pattern was initially attributed to deep or midline cerebral lesions resulting from increased intracranial pressure, although it was later described in association with several other structural and metabolic encephalopathies. This pattern is not necessarily related to deep midline lesions and can be associated with tumors of the posterior fossa and third ventricle [4,5], subcortical lesions [6], cerebral edema [7], metabolic encephalopathy caused by uremia and liver failure [8], basilar ⁎ Department of Neurological, Neuropsychological, Morphological and Movement Sciences, University of Verona, Piazzale L.A. Scuro, 37134 Verona, Italy. Fax: + 39 0458124873. E-mail address: [email protected]. 1525-5050/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.yebeh.2010.11.009

artery migraine [9,10], corticobasal degeneration and progressive supranuclear palsy [11], Creutzfeld–Jacob disease [12–14], and dementia with Lewy bodies [15,16]. FIRDA may also be recorded in otherwise normal subjects during hyperventilation [17], and is probably secondary to functional changes induced by hypocapnia [18]. This EEG pattern is not likely to be epileptic in nature, although it may be associated with epileptiform activity in less than 2% of patients. Kubota and Ohnishi [19] conducted a study to evaluate the clinical correlations of FIRDA among patients with epilepsy. They concluded that patients with 1.5- to 2.5-Hz FIRDA were older and partial epilepsy was most common, compared with patients with 3-Hz FIRDA, who were younger and had idiopathic generalized epilepsy. In a retrospective study, Watemberg et al. [20] suggested that FIRDA may occur during mild to moderate metabolic impairment (often renal failure and hyperglycemia) in awake patients with previous structural brain injury (most commonly diffuse and localized ischemic lesions). A recent prospective study [21] found a relatively high prevalence of FIRDA (6%), with encephalopathy and structural brain lesions being independently related to this EEG pattern. No specific etiology of encephalopathy associated with FIRDA was determined, although renal failure was frequently reported. FIRDA was also observed with cortical and deep tumors, strokes, and other focal brain lesions and, thus, was not associated with specific cerebral locations. The origin and significance of this activity are still unclear. FIRDA was initially considered a projected rhythm originating from subcortical, deep midline structures, although subsequently it has been suggested that this pattern may reflect a pathological hyperactivity occurring in diffuse gray matter disease, in both cortical and subcortical locations [22,23], whereas polymorphic irregular localized delta activity occurs in focal white matter lesions or in thalamic lesions [24].

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Fig. 1. Frontal intermittent rhythmic delta activity (FIRDA) in a 76-year-old woman with intraventricular hemorrhage. FIRDA consists of a run of synchronous, rhythmic 1.5-2 Hz delta waves with a bifrontal preponderance.

3. Temporal intermittent rhythmic delta activity Intermittent rhythmic delta activity prevalent over temporal regions is known as TIRDA. TIRDA was originally described by Reiher et al. [25]. It is characterized by short trains of ≥3 seconds of intermittent, rhythmic, saw-toothed or sinusoidal, 1- to 4-Hz activity of 50–100 μV in amplitude, recorded predominantly over the anterior temporal regions [25,26], and occurring more frequently during drowsiness and light sleep. When occurring bilaterally and independently, TIRDA may vary from side to side and is often associated with anterior temporal spikes or sharp waves (interictal epileptiform discharges), particularly during sleep [25]. This pattern was initially considered indicative of complex partial epilepsy, particularly originating from temporal lobe [26–28]. A straight correlation between short (1–6 seconds) TIRDA with a spike focus and mesiotemporal atrophy assessed by volumetric MRI has been reported [27,29]. Although TIRDA was initially thought to be related to extratemporal epilepsy [28], later studies did not confirm this, suggesting that this pattern might be considered an EEG marker of an epileptogenic zone involving the mesial structures of the temporal lobe [30]. As a consequence, in contrast to FIRDA and OIRDA, TIRDA is highly indicative of ipsilateral pathology. It also has great diagnostic specificity and high positive predictive value for mesial temporal lobe epilepsy [25]. It may therefore be considered an interictal potentially epileptogenic pattern possibly with the same epileptogenic significance as temporal lobe spike or sharp-wave discharges. Persistent polymorphic delta activity over the temporal region is usually due to a focal structural brain injury and should be differentiated from TIRDA, as it may not be potentially epileptogenic. 4. Occipital intermittent rhythmic delta activity Occipital intermittent rhythmic delta activity was originally described in patients with absence seizures by Cobb in 1945 [1]. This typical EEG pattern occurs almost exclusively in children. Initially, this EEG pattern was considered the occipital equivalent of FIRDA, the different location being an age-related expression of the same pathophysiological process [1,31] which depends on maturational factors. Hyperventilation

induces slow activity that is posterior dominant in children and anterior dominant in adults, thus reflecting maturational changes. Something similar is thought to occur with OIRDA in children and FIRDA in adults [32]. It was later suggested that OIRDA is probably an epileptiform interictal pattern frequently associated with primary generalized epilepsy [33], such as generalized tonic–clonic and absence seizures [32,34], and with localization-related epilepsy [32,35]. The high correlation with epilepsy makes OIRDA more similar to TIRDA than to FIRDA [32]. However, OIRDA is not pathognomonic of epilepsy, as it has also been reported in juvenile Huntington's disease [36], central nervous system salmonellosis [37], and subacute sclerosing panencephalitis [35]. OIRDA must be differentiated from phi rhythm. Phi rhythm, which was described by Belsh et al. [38] as “posterior rhythm slow activity after eye closure,” is a brief (1–3 seconds), paroxysmal, bisynchronous occipital delta rhythm that includes at least three monomorphic delta waves within 2 seconds of eye closure on at least two occasions during electroencephalography [39]. It has a frequency of 2 to 4 Hz and an amplitude of 100 to 250 μV. Although its EEG features resemble those of OIRDA, it differs because it is triggered by eye closure and because it is not associated with epilepsy, unless a spike component is present. The mechanism underlying the phi rhythm is unclear, but it has been suggested that such a rhythm may originate from subcortical regions [39]. Conflict of interest statement There is nothing to disclose. References [1] Cobb WA. Rhythmic slow discharges in the electroencephalogram. J Neurol Neurosurg Psychiatr 1945;8:65–78. [2] Van der Drift JH, Magnus O. The value of the EEG in the differential diagnosis of cases with cerebral lesions. Electroencephalogr Clin Neurophysiol 1959;11:733–46. [3] Zurek R, Delgado JS, Froescher W, Niedermeyer E. Frontal intermittent rhythmical delta activity and anterior bradyrhythmia. Clin Electroencephalogr 1985;16:1–10. [4] Faure J, Droogleever-Fortuyn J, Gastaut H, et al. Genesis and significance of rhythms recorded at a distance in cases of cerebral tumors. Electroencephalogr Clin Neurophysiol 1951;3:429–34. [5] Daly D, Whelan JL, Bickford RG, MacCarty CS. The electroencephalogram in cases of tumors of the posterior fossa and third ventricle. EEG Clin Neurophysiol 1953;5: 203–16.

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