Seizure focus

A low dosage of progestin ( mini-pill ) is used, in the form of medroxyprogesterone acetate, which is active at a very low dose. The mini-pill does not inhibit ovulation, but rather interferes with the endometrium and the cervical mucus. The use of this pill prevents most of the side effects of oral contraception, specifically nausea, water retention, and in some cases thrombophlebitis. However, a lower success rate and other frequent side effects have reduced the widespread acceptance of this preparation. Nevertheless, the mini-pill has a role to play in certain specific situations. For example, in an uncommon form of epilepsy called catamenial epilepsy, female patients will experience seizures at particular times during their menstrual cycle, reflecting the fact that seizure focus is stimulated by estrogens but inhibited by progestins. In such women, the mini-pill may afford not only birth control but also improved seizure control. 

SPECT has been found to be quite useful when evaluating patients with seizures (McNally et al., 2005 Tae et al., 2005). SPECT imaging is commonly used for the ictal study of seizure patients in order to define areas that are the seizure focus. It has in general been much easier to perform ictal SPECT than ictal PET. Advanced analytical techniques of SPECT imaging have helped to improve the data analysis and utilization of the SPECT data in the evaluation of seizure patients but further improvements and validation of the techniques are required (Knowlton et al., 2004). 

Theodore WH, Sato S, Kufta CV, Gaillard WD, Kelley K (1997) FDG-positron emission tomography and invasive EEG Seizure focus detection and surgical outcome. Epilepsia 38 81-86. 

Seizures occur more infrequently in horses than in dogs and cats. Seizures are seen in adult horses from brain trauma, bacterial meningitis, viral encephalitis and, rarely, hepatic encephalopathy or vascular accidents. Convulsions are seen in young neonatal foals with NMS as a result of brain hypoxia and in Arabian foals aged 3-9 months (idiopathic Arabian epilepsy). Anticonvulsant therapy is used to prevent the spread of the seizure focus, increase (raise) the seizure threshold and decrease the electrical excitement of abnormal... 

Phenobarbital is the most commonly used anticonvulsant in horses as it has effects at doses lower than those that produce sedahon. It potentiates the actions of gamma-aminobutyric acid (GABA), the inhibitory neurotransmitter in the CNS. Neuronal stabilization by GABA in postsynaptic neurons occurs from increased intracellular chloride conductance, which hyperpolarizes the membrane the overall result is an increase in the seizure threshold and a decrease in the electrical activity of the seizure focus. 

Technetium ( Tcj Bicisate Injection. A sterile colorless solution of bicisate is complexed with Tc-99m pertech-neuite after reduction with a stannous salt. The precise structure of the technetium complex is fN,N -ethylene-di-L-cy.steinato(3-) oxo "Tc]technetium(V) diethyl ester. This radiopharmaceutical is a neutral and lipophilic complex that crosses the blotxl-brain barrier and is selectively retained in the brain. Therefore, this radiotracer is used as a brain-perfusion imaging agent. After intravenous injection of 20 mCi (740 MBq) of Tc-99m bicisate, about 5% of the injected dose is localized within the brain cells 5 minutes after injection and demonstrates rapid renal excretion (74% in 24 hours). This radiotracer is used clinically to evaluate dementia, stroke, lack of brain perfusion ("brain death"), cerebral vascular reserve, or risk of stroke (acetazolamide challenge. study) and to localize a seizure focus for surgical removal. 

Steinbaugh L, Szaflarski JP. Adjunctive therapy for the treatment of primary generalized tonic-clonic seizures focus on once-daily lamotrigine. Drug Des Dev Ther 2010 4 337-A2. 

Figure 5. Cross-sectional microscope images (20X) of hypothesized PpIX fluorescence in rat hippocampus. When compared to control (A), the seizure focus (B) in a rat kindling model of epilepsy shows a dramatic increase in fluorescence at 635 nm using 400 nm excitation light.

Anticonvulsants or antiepileptics are agents that prevent epileptic seizures or modulate the convulsant episodes eflcited by seizure activity. Certain of these agents, eg, the BZs, are also hypnotics, anxiolytics, and sedatives, reinforcing the possibiUty of a common focus of action at the molecular level (1). 

Complex partial seizures manifest themselves as bizarre behaviours which are also known as psychomotor or temporal lobe epilepsy, since a lesion (focus) is often found in that brain area. Repetitive and apparently purposeful movements vary from simple hand clenching or rubbing to more bizarre hand movements and walking. These can last a few minutes, often disrupt other ongoing activity or speech and the patient has no subsequent memory of them. Complex seizures may develop from simple ones. 

A seizure is accompanied by a burst of spikes in the EEG. Between these so-called iclal phases are solitary EEG interictal spikes. Each of them represents the field potential associated with a burst of action potentials in a group of neurons within the epileptic focus (Fig. 16.2). 

From this survey it is clear that just as normal neuronal function requires appropriately balanced inhibitory and excitatory controls so the generation of interictal spikes depends on disturbances in both. Clearly activity cannot spread without the activation of excitatory circuits, in which NMDA receptors play an important role, but it will be much facilitated by reduced inhibition (Masukawa et al. 1989). These observations may help to explain the establishment of a focus and the development of the interictal spike, but why activity can only spread to seizure proportions, at certain times, is less clear. It will, however, again require overactivity of excitatory circuits inadequately controlled by inhibitory processes. Since these controls are mediated by... 

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