Alvaro R. Gutierrez

Electrodiagnosis of infantile botulism.

Analysis of the literature on the electrophysiologic features of infantile botulism was undertaken. Small compound muscle action potential amplitude is a very sensitive feature but lacks specificity. The decremental response to 2- to 3-Hz repetitive nerve stimulation is inconsistent and not a reliable sign. Tetanic and posttetanic facilitation are highly sensitive and highly specific. Absence of posttetanic exhaustion is also highly specific for infant botulism and shared only by hypermagnesemia. We conclude that the findings of low compound muscle action potential amplitude in combination with tetanic facilitation or posttetanic facilitation and absence of posttetanic exhaustion constitute the triad on which the electrodiagnosis of infantile botulism can be supported.

Topical Review: Electrodiagnosis of Infantile Botulism

Analysis of the literature on the electrophysiologic features of infantile botulism was undertaken. Small compound muscle action potential amplitude is a very sensitive feature but lacks specificity. The decremental response to 2- to 3-Hz repetitive nerve stimulation is inconsistent and not a reliable sign. Tetanic and posttetanic facilitation are highly sensitive and highly specific. Absence of posttetanic exhaustion is also highly specific for infant botulism and shared only by hypermagnesemia. We conclude that the findings of low compound muscle action potential amplitude in combination with tetanic facilitation or posttetanic facilitation and absence of posttetanic exhaustion constitute the triad on which the electrodiagnosis of infantile botulism can be supported. (J Child Neurol 1994;9:362-365).

Dipole Reversal: An Ictal Feature of Benign Partial Epilepsy with Centrotemporal Spikes

Summary: Benign epilepsy with centrotemporal spikes (BECTS) is characterized by brief stereotypical partial seizures with motor and/or sensory symptoms with frequent secondarily generalized seizures. The interictal EEG shows slow, disphasic, high‐voltage spikes in the centrotemporal areas. The few published examples of ictal tracings depict focal rhythmic sharp waves and spikes without significant postictal slowing. We report an ictal event in BECTS that is unusual in the evolution and polarity of the ictal discharges. In this subclinical seizure, ictal multiple spike and wave discharges appear as a dipole: they are electropositive in T3‐C3 and negative in F3. These surface positive epileptic discharges are unique and require explanation. We postulate that the seizure discharge arises in the depths of the sylvian fissure involving folded cortical areas. This occurs in such a way that the negative component of the discharges is concealed from the scalp electrodes. Thus, a relative positivity is recorded on the surface. This represents a dipole reversal relative to the interictal discharges (characteristic of BECTS). This geometrical explanation allows us to avoid postulating an unusual mechanism of generation of this seizure.

Rolandic epilepsy and cortical dysplasia: MRI correlation of epileptiform discharges

An 8 year-old girl presented with simple facial motor seizures. Although the electroencephalogram (EEG) demonstrated left hemisphere centrotemporal spikes with features consistent with benign rolandic epilepsy, magnetic resonance imaging (MRI) indicated a left hemisphere focal cortical dysplasia. MRI-assisted EEG dipole analysis of the spikes suggested that the rolandic fissure rather than the focal cortical dysplasia was the origin of the epileptic spike discharge. This noninvasive method may be a useful adjunct in evaluation of some patients with epilepsy and focal superficial cerebral lesions.

EEG and pathologic findings in patients undergoing brain biopsy for suspected encephalitis

Previous studies have suggested that EEG may be helpful in the diagnosis of herpes encephalitis (HE). To further define the value of EEG in an acutely ill, febrile, encephalopathic patient suspected as having encephalitis, we reviewed initial preoperative EEGs with the results of cerebral biopsies in 24 consecutive patients suspected of having encephalitis. Statistical analysis demonstrated that EEG patterns have only limited association with biopsy results. Since diseases which mimic encephalitis may also generate identical EEG changes, this is not an unexpected finding. EEG is useful in the evaluation and management of patients with encephalitis. However, the absence of specific wave forms or focal EEG abnormalities in the proper clinical setting should not deter consideration of HE or delay treatment.

Seizures and Electrolyte Imbalance

Although electrolyte imbalance is commonly encountered in clinical practice, associated seizures occur infrequently. Indeed, the finding of an electrolyte imbalance in the setting of new-onset seizure activity should not preclude a search for other potential causes of seizures. An important clinical caveat is that seizures secondary to electrolyte abnormalities can be either partial or generalized. In this chapter, disturbances of serum sodium, magnesium, potassium, and calcium will be reviewed with regard to their propensity to provoke seizures. The causes of electrolyte imbalance and the pathogenesis and treatment of associated seizures will be discussed.