What are the diagnostic criteria for juvenile myoclonic seizures?

Diagnostic Criteria for Juvenile Myoclonic Epilepsy

Juvenile myoclonic epilepsy (JME) is diagnosed based on a characteristic clinical triad: bilateral myoclonic jerks (especially upon awakening), generalized tonic-clonic seizures in approximately 90% of patients, and absence seizures in about one-third of cases, with seizure onset during adolescence around puberty. 1, 2, 3

Clinical Diagnostic Features

Core Seizure Types (Must Have Myoclonic Jerks)

• Myoclonic seizures are mandatory for diagnosis - bilateral jerks without loss of consciousness, typically the debut symptom 1, 2
• Generalized tonic-clonic seizures (GTCS) occur in approximately 90% of patients, usually appearing after myoclonias have been present 1, 2
• Absence seizures are present in approximately one-third of patients 1, 3

Characteristic Temporal Pattern

• Seizures occur predominantly after awakening from sleep or during evening relaxation periods 2, 3
• Sleep deprivation is the most common precipitating factor, followed by fatigue, sudden arousal, alcohol consumption, and photic stimulation 4, 3

Age of Onset

• Seizure onset occurs during adolescence, typically around the time of puberty 2, 3

EEG Diagnostic Criteria

Ictal EEG Pattern

• The ictal EEG shows a typical 4-6 Hz polyspike and wave pattern, which is highly characteristic of JME 3, 1

Interictal EEG Findings

• Routine awake EEGs are abnormal in only 73% of cases and may be misleading in approximately 7% 4
• Sleep EEG is 100% sensitive and shows generalized spikes, polyspikes, and slow wave discharges 4
• Discharge rates increase significantly during the sleep-to-awakening transition phase, which is considered a specific finding in the appropriate clinical setting 4
• Focal EEG abnormalities may be seen in approximately 30% of patients, which can lead to misdiagnosis as focal epilepsy 1

Neuroimaging Findings

• Neuroimaging is typically normal - patients have normal physical and neuroradiological findings 5
• MRI is rarely indicated in neurologically normal patients with typical generalized seizures like JME because the rate of positive intracranial findings is low given their genetic underpinnings 6, 7
• Only 2% of low-risk patients (those without predisposing conditions or focal features) have abnormal MRI findings 6

Common Diagnostic Pitfalls

Underdiagnosis and Misdiagnosis

• There is typically a delay of 3.5 years in diagnosis due to patients not spontaneously reporting myoclonic jerks 4
• Physicians must specifically ask about morning jerks, as most patients do not report them without direct questioning 1
• JME is frequently misdiagnosed as focal epilepsy due to focal EEG abnormalities in 30% of cases or focal features in seizure semiology 1, 5
• The typical diagnostic scenario is a teenager presenting with their first GTCS, and only upon detailed questioning do they reveal a history of morning myoclonic jerks 2

Clinical Approach

• A first GTCS episode in a teenager should be considered JME until proven otherwise, given how common this syndrome is 2
• When focal epilepsy is incorrectly diagnosed, patients may receive antiepileptic drugs that aggravate seizures rather than control them 1

Family History

• A positive family history of epilepsy is often present, reflecting the genetic basis of this syndrome 5