This is a reliable test for the diagnosis of absence seizures: a patient suspected of typical absences should be asked to hyperventilate for three minutes, counting breaths. During hyperventilation, the oxygen and carbon dioxide level will become abnormal. This results in weakening of electrical signal which leads to a reduction in the seizure threshold. Intermittent photic stimulation may precipitate or facilitate absence seizures; eyelid myoclonia is a common clinical feature.A specific mechanism difference exists in absence seizures in that T-type Ca++ channels are believed to be involved. Ethosuximide is specific for these channels and thus it is not effective for treating other types of seizures. Valproate and gabapentin (among others) have multiple mechanisms of action including blockade of T-type Ca++ channels, and are useful in treating multiple seizure types. Gabapentin can aggravate absence seizures. Pathophysiology
The corticothalamic cortical circuit plays an important role in the pathophysiology of absence seizure. Some of the neurons are important in their occurrence. They are

Cortical glutamatergic neurons
Thalamic relay neurons
Neurons of thalamic nucleus reticularisAbnormal oscillatory rhythms develop in the thalamic nucleus reticularis. This causes inhibition of GABAergic neurotransmission and excitation of glutamate neurotransmission. Abnormal oscillatory spikes are produced by the low threshold T-type calcium channel. This explains how inheritance of gene code for T-type calcium channel leads to an absence seizure. Antiepileptic drugs such as Gabapentin, Tiagabine and Vigabatrin cause inhibition of GABA results in exacerbation of absence seizures. Diagnosis
The primary diagnostic test for absence seizures is electroencephalography (EEG).
After World War II the use of penicillin to treat syphilis made general paresis a rarity: even patients manifesting early symptoms of actual general paresis were capable of full recovery with a course of penicillin. The disorder is now virtually unknown outside developing countries, and even there the epidemiology is substantially reduced. Some notable cases of general paresis: 

General Ranald S. Mackenzie was retired from the US Army in 1884 for "general paresis of the insane" 5 years before his death in 1889. Theo Van Gogh, brother of painter Vincent van Gogh, died six months after Vincent in 1891 from "dementia parylitica" or what is now called syphilitic paresis.The Chicago gangster Al Capone died of syphilitic paresis, having contracted syphilis in a brothel in 1919, and not having been properly treated for it in time to prevent his later onset of syphilitic paresis. See also
Karolina Olsson
Neurosyphilis
Tabes dorsalis
Tuskegee experiment

References


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