What are the clinical features of focal seizures?

Clinical Features of Focal Seizures

Focal seizures arise from abnormal epileptic firing in localized brain regions and present with a wide spectrum of clinical manifestations ranging from motor symptoms to altered consciousness, with the key distinguishing feature being that they originate within networks of a single cerebral hemisphere. 1

Core Distinguishing Characteristics

• Focal seizures originate from one hemisphere and may remain localized or subsequently spread to become bilateral, unlike generalized seizures which rapidly affect both hemispheres from onset 1
• The presence of any focal feature to a seizure is independently associated with clinically relevant abnormalities on neuroimaging, making recognition of these features critical 2
• Focal seizures have a recurrence rate up to 94%, considerably higher than generalized seizures at 72% 2

Clinical Manifestations by Category

Motor Features

• Focal motor seizures are among the most common presentations, often manifesting as continuous jerking motor activity in a localized body region 3
• Hemiparesis is the most frequent focal neurological sign when focal brain injury occurs from venous ischemia or hemorrhage 2
• Brief focal seizures with orofacial involvement and mouth deviation are characteristic of specific syndromes like Benign Rolandic Epilepsy 4

Sensory and Cortical Signs

• Sensory symptoms referable to the affected brain region commonly occur alongside motor manifestations 2
• Aphasia frequently accompanies focal seizures when language-dominant regions are involved 2
• Other cortical signs including visual field defects, psychosis (in conjunction with focal signs), and specific sensory disturbances may manifest depending on seizure localization 2

Altered Consciousness

• Focal seizures with impaired awareness (formerly complex partial seizures) represent a major subtype where consciousness is affected despite focal origin 2
• Abnormal mental status is one of the most common manifestations at the time of EEG diagnosis, even when obvious motor activity is absent 3

Critical Diagnostic Pitfalls

Seizures Without Obvious Clinical Signs

• Three out of 41 patients with focal status epilepticus had no obvious clinical seizures, demonstrating that focal seizures can occur without visible manifestations 3
• The diagnosis of focal status is often delayed or missed in 28 of 41 patients before EEG confirmation, particularly when patients present primarily with altered mental status 3
• Focal status should be suspected after strokes or clinical seizures when patients do not stabilize or improve as expected 3

Bilateral Involvement Does Not Exclude Focal Origin

• Bilateral motor signs, including paraparesis, may occur with focal seizures due to sagittal sinus thrombosis and bihemispheric injury, potentially mimicking generalized seizures 2
• Bilateral thalamic involvement from deep venous system thrombosis can cause alterations in consciousness without focal neurological findings, confounding the clinical picture 2

Temporal Presentation Patterns

• Focal seizures may present acutely (<48 hours), subacutely (>48 hours to 30 days), or chronically (>30 days), with subacute presentation being most common at 56% 2
• Median delay from symptom onset to diagnosis is 7 days, highlighting the diagnostic challenge these seizures present 2

Associated Seizure Activity

• Focal or generalized seizures occur in 40% of patients with cerebral venous thrombosis, making seizures a frequent feature when focal pathology is present 2
• Focal seizures may evolve to bilateral tonic-clonic seizures (focal to bilateral), which starts focally then propagates to both hemispheres 2

Underlying Structural Associations

• Focal seizures show considerably higher positive neuroimaging yields compared to generalized seizures in neurologically normal patients 2
• Structural brain lesions commonly associated with focal seizures include tumors, infection, infarction, traumatic brain injury, vascular malformations, developmental abnormalities, and seizure-associated brain pathology 1
• Approximately 4% of children with first-time afebrile focal seizures have urgent intracranial pathology, most commonly infarction, hemorrhage, and thrombosis 2

EEG Characteristics

• Focal seizures show ictal discharges originating from one hemisphere on EEG, which is the electrographic hallmark 1
• EEG patterns may show either discrete recurrent focal electrographic seizures or rapid continuous focal epileptiform discharges, both of which should be interpreted as focal status epilepticus with similar clinical significance 3