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Focal abnormalities detected by 18FDG PET in epileptic encephalopathies
  1. M A CLARKE
  1. Department of Paediatric Neurology
  2. Booth Hall Children’s Hospital
  3. Charlestown Road, Blackley
  4. Manchester M9 7AA

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    Editor,—Ferrie et al state that ‘seizures in the epileptic encephalopathies are usually considered to be primary generalised...’.1 However the term ‘primary generalised’ should be used to refer to particular forms of epilepsy not seizures.

    The international classification of epilepsies, epileptic syndromes, and related seizure disorders classifies epilepsies as having generalised or partial seizures.2 Furthermore epilepsies are classified as symptomatic (having a known aetiology), idiopathic (no underlying cause other than a possible inherited predisposition), or cryptogenic (occult or hidden cause presumed to be symptomatic but aetiology is not known).

    Idiopathic epilepsies are also designated primary. The primary epilepsies have no structural or biochemical cause, are genetically transmitted, and have a better prognosis for seizure control than symptomatic or cryptogenic epilepsies. Examples of primary generalised epilepsies are childhood absence epilepsy, epilepsy with grand mal on wakening.

    Lennox-Gastaut syndrome, severe myoclonic epilepsy in infancy, and myoclonic astatic epilepsy are not examples of primary generalised epilepsies. They are cryptogenic epilepsies. The term primary generalised refers to type of epilepsy not to type of seizure. Seizures are partial or generalised or unclassifiable. Examples of generalised seizures include absence, myoclonic, clonic, tonic, tonic-clonic, and atonic seizures.

    This matter of classification of epilepsies and seizures if often perceived as arcane. It is not. It is of importance that doctors treating epilepsy make all efforts to classify a child’s epilepsy because from this arise decisions about appropriate investigation, likely prognosis, risk of recurrence, etc and allows proper selection of study populations.

    Seizures in the epileptic encephalopathies are generalised but the term primary generalised is not appropriate. Furthermore the epilepsies included in the term epileptic encephalopathies are cryptogenic generalised epilepsies not primary generalised epilepsies.

    Drs Ferrie and Panayiotopoulos and Professor Robinson comment:

    We welcome the comments of Dr Clarke regarding the significance of the syndromic diagnosis of epilepsies which our team has previously emphasised.1-3 1-4

    Regarding terminology, the terms ‘primary’ and ‘secondary’ epilepsies/syndromes are obsolete and have been abandoned for over 10 years ‘because their meaning has been frequently misunderstood’.1-5 In both the 19851-5 and 19891-2 international classifications ‘primary’ was replaced with ‘idiopathic’, ‘secondary’ with ‘symptomatic’. The only occasion in which one of these terms is used is in the seizure classification1-6 for ‘secondarily’ generalised seizures implying an initial partial (focal) seizure progressing to a generalised one.1-6 It was in this sense that we used the term primary (primarily) generalised seizures in order to emphasise that the seizures of our patients appeared to be generalised from onset and not partial followed by secondarily generalisation. It is absolutely clear in our report that the children studied had cryptogenic epilepsy syndromes. In conclusion, we totally agree with Dr Clarke that the appropriate terminology and syndromic diagnosis should be strictly applied in epilepsies as in all other fields of medicine.

    References

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