Todd’s paresis describes post-ictal motor deficits. This means development of weakness / paralysis of part of the body following a focal seizure. It is a common stroke mimic and medical school exam favourite. History (as always!) is key.
In clinical practice, the classic presentation is weakness of the contralateral limb to the area of seizure activity. This may range from mild weakness to overt paralysis (hence the concern about stroke!). Depending on the area of brain affected by seizure activity, a range of other clinical features may be present including speech or sensory disturbances.
The condition occurs following focal seizures. This may be secondary to a pure focal seizure, where the seizure activity remains localised to a single area. Alternatively, it can occur due to a focal-onset seizure that can extend to other areas of the brain.
The condition itself is theorised to develop due to ‘exhaustion’ of the cerebral area affected by vigorous depolarisation. This leads to a prolonged refractory state in that area. Another theory is the presence of prolonged local inhibition, which acts to prevent further seizure activity. Alternatively, it may be due to reduced blood flow from vasoconstriction, which limits the function of the area.
Recovery is usually within minutes to days and the vast majority within 36 hours. Many patients, depending on brain area involved, risk factors and collateral history, will need to have stroke excluded. MRI helps differentiate from an acute stroke and sometimes reversible post-ictal perfusion abnormalities will be identified. Another differential to consider is hemiplegic migraine, which classically presents as a severe, unilateral headache associated with hemiparesis.