This chapter focuses on rhythmic and periodic patterns (RPPs). These are common EEG patterns found in critically ill patients. The variety of different types of patterns and their standardized naming conventions are described here. These patterns span from serving as markers of encephalopathy, to markers of seizure risk (interictal), to status epilepticus itself (ictal), and everything in between. This broad potential of diagnostic significance is known as the ictal–interictal injury continuum (IIIC). This chapter describes strategies for differentiating between more benign and more malignant RPPs. Basic management strategies for these IIIC patterns are also described in this chapter.

Pediatric epilepsy is a broad topic with specific syndromes highlighted in this chapter. A thorough discussion for the evaluation and management of febrile seizures is first. The chapter then transitions to a discussion of high-yield epileptic and developmental encephalopathies. Examples include diagnoses like infantile spasms, Dravet syndrome, and FIRES (febrile infection-related epilepsy syndrome). The chapter than progresses toward the self-limiting epilepsy of childhoods and a discussion of clinical features, management, and long-term prognosis.The generalized epilepsies are then discussed since they commonly commence in the pediatric time period. High-yield EEG examples are provided as they so frequently confirm the diagnosis. Specific neurocutaneous syndromes are next reviewed in a concise table that defines key differences and diagnostic criteria.Lastly, the two diagnoses of Rasmussen’s encephalitis and hemimegaloencephaly that can benefit from early consideration of hemispherectomy are reviewed.

First-time seizures are a common part of neurology practice. Making an accurate and specific diagnosis is achievable by taking an excellent history. Clinicians should keep in mind that seizures are only part of the differential in a patient with a first-time event, with other diagnoses like syncope common as well. This history should focus on what the seizure feels like to the patient and looks like to observers. Two classification systems, the seizure semiology and International League Against Epilepsy (ILAE), exist to make communicating complex information easier. Key semiology history includes the presence or absence of auras, altered awareness, or convulsions. In addition to history, laboratory, EEG, and imaging data can inform to the specific patient diagnosis. If you determine that the patient has had a first-time seizure without a clear epilepsy diagnosis, you can tell them seizure that the recurrence risk is 40%. If you determine the patient has epilepsy, you can tell them that 50% of people are seizure-free with the first medication used. Patients should be reassured that they can live normal lives with most jobs being obtainable and family life being a possibility if the patient so chooses.

A seizure is defined as abnormally coordinated electrical activity that is clinically noted as abnormal sensations, movements, or behaviors. Epilepsy is defined as the tendency to have seizures, practically as two unprovoked seizures at least 24 hours apart or one seizure with a 60% chance of additional seizures. The two overall epilepsy types are generalized and focal. Focal epilepsy most commonly indicates a focal brain injury like traumatic brain injury or tumor. In contrast, generalized epilepsy is due to a genetic etiology, not necessarily inherited. An epilepsy diagnosis is clinically made and can be supported by typical EEG and MRI findings. Nearly 4% of people develop epilepsy, with the largest peak during later years and the second peak during childhood. Nearly 70% of people are seizure-free after five years, whether via control with medications or, less commonly, the epilepsy itself remits. Life expectancy for epilepsy patients is lower. A key contributor to epilepsy mortality is sudden unexpected death in epilepsy (SUDEP). Uncontrolled generalized tonic clonic seizures are a key risk factor for SUDEP.

Repetitive waveforms may repeat in quick succession (rhythmic) , after nearly regular intervals (periodic), or spike and wave (SW). Periodic discharges are considered markers for neuronal injury. Most forms of repetitive abnormalities are epileptogenic; in specific situations they may also represent ictal patterns. GSW discharges of more than 3 Hz or other evolving discharges of more than 4 Hz are unequivocally ictal patterns, whereas GSW of less than 3 Hz or other evolving discharges of less than 4 Hz lie on an ictal-interictal spectrum. This means that these patterns may or may not be ictal depending on their clinical and electrographic accompaniments. A repetitive pattern is described as a combination of a main term 1 with a main term 2 based on the American Clinical Neurophysiology Society (ACNS) standardized critical care EEG terminology. Main term 1 could be either generalized (G), lateralized (L), bilateral independent (BI), or multifocal (Mf). Main term 2 could be either periodic discharges (PD), rhythmic delta activity (RDA), or generalized spike-wave (GSW). Common rhythmic abnormalities include GRDA and LRDA. Common periodic abnormalities include GPDs, LPDs, and BIPDs.The term “SI” is added to the combination of main terms to denote a stimulus-induced pattern (e.g., SI-GPDs for stimulus-induced GPDs).

Seizures (epileptic) are manifestations of transient abnormal excessive or synchronized cerebral neuronal activity. Seizures may be provoked (acute conditions) or unprovoked (epilepsy). Seizures are classified as focal or generalized onset based on consistent clinical observation, EEG and imaging findings. Focal onset seizures originate from a single hemisphere while generalized seizures originate from bilateral hemispheres. Focal seizures may be further classified based on impairment of awareness (anytime during seizure) and motor or non-motor activity (at the very onset). Focal seizures without impaired awareness may not have surface EEG abnormalities. Focal seizures may secondarily generalize, these are now called focal to bilateral tonic clonic seizures. Generalized seizures are associated with impaired awareness, hence only motor or non-motor activity at onset is used to classify them. Common generalized motor seizures include generalized tonic clonic seizures (GTCs), tonic, atonic, myoclonic, myoclonic-atonic and epileptic spasms. Common generalized non-motor seizures include typical and atypical absences, myoclonic absences and absences with eyelid myoclonia.

Generalized continua represent a class of models whose potential applicability seems to have been underestimated. The mathematical structure of these models is discussed and the reasons why it has been underestimated are made clear. Their importance in the theory of metamaterials is highlighted and their potential impact on future technological applications is carefully argued. It is shown how the original ideas of Lagrange and Piola can be developed by using the modern tools of differential geometry, as formulated by Ricci and Levi-Civita. It has to be concluded that variational principles are the most powerful tool also in the mathematical modeling of metamaterials.