A 32-year-old woman with a 5-year history of seizures is being evaluated for drug-resistant epilepsy. Her neurologist is considering whether her seizures are primary generalized tonic-clonic (PGTC) or focal seizures with secondary generalization. Which of the following features best distinguishes primary generalized tonic-clonic seizures from focal seizures with secondary generalization?

Explanation

## Distinguishing PGTC from Focal Seizures with Secondary Generalization ### Key Clinical Discriminator **Key Point:** The most reliable discriminating feature is the **nature of seizure onset** — primary generalized tonic-clonic seizures begin with immediate, bilateral loss of consciousness *without* focal onset, whereas focal seizures with secondary generalization always begin focally (with or without awareness) before spreading. ### Comparative Table | Feature | Primary Generalized TC | Focal → Secondary Generalization | | --- | --- | --- | | **Seizure onset** | Bilateral, simultaneous | Focal (one hemisphere first) | | **Aura/prodrome** | Absent | Often present (focal semiology) | | **Initial consciousness** | Lost immediately | May be preserved initially (focal aware) | | **Postictal confusion** | Common, 30–60 min | Common, 30–60 min | | **Todd's paralysis** | Absent | May occur (focal motor cortex involvement) | | **Interictal focal signs** | Absent | May be present (structural lesion) | | **EEG: generalized spike-wave** | Yes (3 Hz) | No; focal spike focus | | **Imaging** | Normal | May show focal lesion | ### Why Option 2 Is Correct **High-Yield:** Immediate loss of consciousness at onset *without* focal prodrome or aura is pathognomonic for primary generalized seizures. The seizure begins as a bilateral phenomenon from the start, affecting both hemispheres simultaneously. This is the defining electroclinical feature. ### Why the Other Options Are Misleading **Clinical Pearl:** Postictal confusion (option 1) and Todd's paralysis (option 4) are **non-discriminating** — both occur in PGTC and in focal seizures with secondary generalization, depending on the duration and intensity of the ictal discharge. A patient with focal motor seizures that secondarily generalize may have Todd's paralysis in the affected limb. Absence of focal neurological signs (option 3) is also unreliable — many patients with focal seizures have normal interictal neurological exams, especially if the focus is in non-eloquent cortex. ### Diagnostic Confirmation **Key Point:** EEG is the gold standard: PGTC shows **generalized 3 Hz spike-and-wave complexes**, while focal seizures show a **focal spike focus** that may secondarily generalize. Neuroimaging may reveal a structural lesion (tumor, cavernoma, cortical dysplasia) in focal epilepsy but is typically normal in primary generalized epilepsy. [cite:Harrison 21e Ch 369]