A patient develops transient unilateral weakness after a focal seizure; what is the likely diagnosis, recommended imaging, and acute management?

Todd's Paralysis: Diagnosis, Imaging, and Acute Management

Todd's paralysis is a transient postictal focal neurological deficit occurring after a focal or generalized seizure, and the primary acute management priority is to perform emergent neuroimaging (MRI preferred, CT acceptable) to exclude acute stroke, followed by supportive care while awaiting spontaneous resolution over minutes to hours.

Clinical Diagnosis

Todd's paralysis presents as unilateral weakness, paresis, or other focal neurological deficits (aphasia, hemianopsia, sensory loss) immediately following a seizure, lasting from minutes up to 36 hours. 1, 2

• The condition occurs after 6-13% of all seizures, with higher incidence following focal seizures or generalized tonic-clonic seizures 1, 2
• Risk factors include older age, history of prior stroke, and structural cortical damage 2
• The deficit is typically contralateral to the epileptogenic zone 3
• Bilateral Todd's paralysis is exceedingly rare but can occur with midline or bilateral seizure foci 3

Critical Differential Diagnosis Challenge

The primary clinical dilemma is distinguishing Todd's paralysis from acute ischemic stroke with seizure at onset—a differentiation that cannot be made reliably on clinical grounds alone. 1, 4

• Both conditions present with acute focal neurological deficits 1, 4
• Stroke can present with seizure at symptom onset, mimicking the clinical sequence of Todd's paralysis 1
• Misdiagnosis carries significant consequences: inappropriate thrombolytic therapy if stroke is incorrectly diagnosed, or missed treatment window if stroke is incorrectly attributed to Todd's paralysis 5

Recommended Imaging Strategy

First-Line Imaging: MRI with Advanced Sequences

MRI is superior to CT for identifying both stroke and the characteristic perfusion abnormalities of Todd's paralysis, and should be the preferred initial imaging modality when immediately available. 6, 7

• MRI may demonstrate transient diffusion restriction (cytotoxic edema) in Todd's paralysis that mimics acute stroke on DWI sequences 4
• The key distinguishing feature is that diffusion restriction in Todd's paralysis resolves on follow-up imaging, whereas stroke-related changes persist 4
• MRI is more sensitive than CT for detecting subtle cortical abnormalities, structural lesions (cortical dysplasia, prior infarcts, tumors), and epileptogenic foci 6
• MR perfusion demonstrates reversible hemispheric hypoperfusion in Todd's paralysis that normalizes as clinical deficits resolve 5

Alternative Imaging: CT with Perfusion

When MRI is not immediately available, non-contrast CT followed by CT angiography and CT perfusion is an acceptable alternative to exclude stroke and characterize perfusion abnormalities. 1, 5

• Non-contrast CT rapidly excludes intracranial hemorrhage 6, 8
• CT perfusion in Todd's paralysis shows dramatic reduction in cerebral blood flow and blood volume in the affected hemisphere, but with preserved mean transit time and no large vessel occlusion—a pattern distinct from acute stroke 5
• CT angiography confirms absence of large vessel occlusion 5
• This perfusion pattern reverses as clinical symptoms resolve, correlating with the transient nature of Todd's paralysis 5

Imaging Protocol Summary

For a patient with transient unilateral weakness after a focal seizure:

1. Emergent MRI brain with DWI, FLAIR, and perfusion sequences (preferred) 6, 7, 5
   • OR emergent non-contrast CT head followed by CT angiography and CT perfusion if MRI unavailable 8, 1, 5
2. If initial diffusion restriction is present, obtain follow-up MRI within 24-48 hours to document resolution (distinguishes Todd's paralysis from stroke) 4
3. Consider MR or CT angiography to exclude vascular occlusion 1, 5

Acute Management

Immediate Stabilization

Assess airway, breathing, circulation, and obtain bedside glucose measurement; confirm the patient has returned to baseline neurological status before making disposition decisions. 7

• Measure serum glucose and sodium immediately—these are the only laboratory abnormalities that consistently alter acute management 7, 9
• Obtain complete metabolic panel only if specific clinical clues (vomiting, diarrhea, dehydration) are present 7

Supportive Care During Deficit Resolution

Todd's paralysis requires only supportive care and observation while awaiting spontaneous resolution; no specific intervention reverses the deficit. 1, 2

• The duration ranges from minutes to 36 hours, with most cases resolving within hours 1, 2
• Monitor neurological status closely; failure to improve or worsening deficits suggests alternative diagnosis 7, 9
• Patients who have not returned to baseline within several hours require emergent neuroimaging if not already performed 7, 9

Antiepileptic Drug Considerations

Do not initiate antiepileptic drugs in the emergency department solely for Todd's paralysis; AED decisions should be based on the underlying seizure disorder, not the postictal deficit. 7

• For first unprovoked seizure without prior brain disease, AED initiation does not improve long-term outcomes and exposes patients to medication adverse effects 7
• Consider AED initiation only when the seizure occurred in the setting of remote symptomatic brain disease (prior stroke, traumatic brain injury, tumor) 7

Disposition Decisions

Patients with Todd's paralysis who have returned to baseline neurological status, have imaging that excludes stroke and identifies an epileptogenic lesion, and have reliable outpatient follow-up can be safely discharged from the emergency department. 7

• Admit patients with persistent neurological deficits, abnormal imaging requiring inpatient management, or unreliable follow-up 7
• Arrange outpatient neurology follow-up and EEG for all patients with new-onset seizures 7

Common Pitfalls to Avoid

The most critical error is assuming focal deficits after a witnessed seizure are automatically Todd's paralysis without imaging to exclude stroke. 1, 4

• Stroke with seizure at onset can present identically to seizure with Todd's paralysis 1
• Do not withhold thrombolytic therapy based solely on clinical suspicion of Todd's paralysis—imaging confirmation is mandatory 5, 4
• Do not misinterpret CT or MR perfusion showing hemispheric hypoperfusion as stroke; check for preserved mean transit time and absence of vessel occlusion, which characterize Todd's paralysis 5
• Do not perform lumbar puncture for uncomplicated Todd's paralysis; reserve LP for suspected meningitis or encephalitis 7
• Be aware that diffusion restriction on MRI can occur in Todd's paralysis and does not definitively diagnose stroke; follow-up imaging showing resolution confirms Todd's paralysis 4