Posttraumatic Epilepsy

W Wallis

CAA Meeting

Wellington 30.8.10

Case History• 38 y.o. commercial pilot seen by neurologist

for ACC. Had a head injury 6 months before. Hospital notes describe injury as trivial. Is he fit to return to work?

• EEG normal. Declared fit to return to flying

• At solo command, flying at 12,000 feet on autopilot, had a major generalized convulsion

• An apprehensive passenger, with a few flying lessons, took over till pilot woke up 10 min later. Landed safely.

• CT brain scan showed old temporal lobe scar with blood products. Diagnosis posttraumatic epilepsy

• What went wrong?

Aero Commander

↓

Fitness is usually self-evident by clinical evaluation

With this important exception

Unrecognized risk of post-traumatic epilepsy (PTE)

• Risk of PTE reasonably predictable and evidence-based.

• Procedure: (1) review of clinical records (2) grade severity of head injury (3) CT brain imaging. Then predict risk of PTE. (consider this in all cases of head injury in aviation setting)

Posttraumatic Epilepsy (PTE)Some Relevant Terms

• Definition of PTE differs from that of epilepsy. PTE requires only one seizure I week after head injury and the not usual 2 or more unprovoked seizures defining epilepsy

• Three types of seizures caused by trauma. Pathophysiology, management, and prognosis are different.

1. Immediate or “concussive” (at instant of injury). Does not predict PTE

2. Early (7 days or less after injury) Dependent variable for prediction PTE

3. Late (onset 7 days to 20 or > yrs later)

PTE refers to late type

Grading Severity of Head Injuries(by review of original medical records)

• Mild: Post traumatic amnesia (PTA) ½ hour or less, no persistent neurological signs or symptoms. Normal CT.

• Moderate: PTA >1/2 hour but < 24 hours, + or - linear fracture, otherwise as per mild head injury. No intracerebral bleeding on CT.

• Severe PTA >24 hours, early epilepsy, depressed fracture, any neurological abnormality, and any post-traumatic intracranial abnormality found on CT brain scan.

Annegers J.F. et al. NEJM 1998; 338:20-24,

Brain Imaging Predicts Risk of PTE

• Traumatic bleeding within the brain is an independent variable predicting PTE.

• Clinical features of injury, such as post traumatic amnesia and early seizures are dependent variables for prediction PTE.

• CT imaging is a specific and sensitive test to detect traumatic intracranial blood products.

D’Alessandro R Arch Neurol 1988; 45: 42-43 and Annegers J.F. et al. NEJM 1998; 338:20-24

Estimation of Initial risk of PTE

• Pre-CT era literature was largely retrospective and proposed complex multifactorial schemes now largely irrelevant.

• Literature in CT era convincingly indicates that traumatic bleeding within the brain is the key independent variable predicting risk of PTE. i.e. contusions and intracerebral blood clots

• Combination of blood products and gliosis predicts PTE in humans and animal models

• Extracerebral and subarachnoid blood, in the absence of intracerebral bleeding or contusion, barely increases risk, if at all.

• A normal CT scan within a few days of head injury = no significant risk of PTE

Pathology of High Risk Brain injuries

CT Prediction of PTE

High risk Acute CT Results

Old Head Injuries: CT Predictions of High Risk for PTE

Low Risk CT

Predicting PTE Some Relevant Terms

• INITIAL RISK: = LIFETIME RISK. ESTIMATED 1 WEEK AFTER HEAD INJURY

• RESIDUAL RISK: = REMAINING RISK AT ANY GIVEN TIME AFTER THE HEAD INJURY. I.E. REMAINING RISK 1, 2 OR > YEARS AFTER INJURY

• AS THE RESIDUAL RISK OF PTE INJURIES DECLINES PROGRESSIVELY WITH TIME, SO THE RESIDUAL RISK IS LOWER AT EACH LATER EPOCH AFTER THE INJURY.

Risk of PTE Declines With TimeJennett 1975, 1000 +, consecutive Pts with head injuries

Interval after injury

Cumulative % of PTE beginning at end of each year

I year 56%

2 years 69%

3 years 77%

4 years 81%

5 years 85%

6 years 88%

7 years 92%

8 years 93%

9 years 95%

10 years 97%

Initial and Residual Risks of PTE ↓ Initial Risk (lifetime) ↓ Residual Risk ↔↓

Cumulative Risk of PTE related to Severity of Injury (Annegers 1998, 4541 pts followed prospectively)

Note that the risk continues up to 20 yrs and differs from controls only with severe head injuries

Relative risk of epilepsy over 10 years in 78,572 Danish people after severe head injury, mild head injury, and skull fracture

compared control reference group

Christensen et al.. Lancet. 2009; 373:1105 -1110

Why estimate the risk? How to do it.

Why?

Consequences of seizure for most people are serious, particularly with certain occupations.

Medico legal Implications.

How?

Clinical and laboratory features of head injuries allow a reasonably accurate estimate of the initial (lifetime) risk as well all the residual risk at any given time after the injury. i.e. an initial risk of 6% will decline to a residual risk of close to 1% in 5 years, but an initial risk of 20% not for 10 years

↓ Initial Risk (lifetime) ↓ Residual Risk ↔↓

A Residual risk of 1% is close to a control risk

An Example of Predicting Initial Risk PTE Annegers J.F. et al. NEJM 1998; 338:20-24 4531 patients followed up to 30 years

Minor injury 2% Up to 30 The risk of PTE is probably the same as the general population.

Moderate injury 4% Up to 30 Some patients probably had unrecognised intracerebral bleeding, as not all had CT scans. The true initial risk of PTE is probably only slightly higher than that of the general population.

Severe injury 11% to 35% Up to 30 Some of these patients did not have intracerebral bleeding but only prolonged amnesia. Those with combined extra and intracerebral bleeding had a risk of 35%. Risk of PTE is this series would probably be higher if those with normal CT scans were removed.

Control population Just below 2%epilepsy

Up to 30 Controls may have a lower risk than subjects prone to head injuries

Type of injury initial risk PTE f/u in yrs Comments

D’Alessandro et al 219 patients all examined with CT scan within 3 days of injury

18 % with only contusions 45% with combined extra and intracerebral bleeding. F/U 5 to 7 years, so risk is higher

Englander et al 647 patients. All had CT scans

Single contusion 8.2%.Multiple contusions 25.2 + % . 60 + % with dural penetration. Combined extra and intracerebral bleeding as well as surgery increased risk PTE further. F/U only 2 years, so risk of PTE is higher than reported

Author % Developing PTE and F/U

Other Examples from Literature Predicting PTE

Predicting PTE: An Example

• Pt has a cerebral contusion, an intracerebral blood clot or an extracerebral collection with underlying blood in brain.

• Initial risk of PTE anywhere from 11% to 60%. CAA uses 20% for contusion

• Residual risk will not approach a control risk for at least 8 years, probably longer

Other Comments

• Role of MRI problematic

• EEG usually not helpful

• Personal review of medical notes and radiology must always be included in clinical evaluation of risk of PTE

• Beware of outdated and misquoted literature. Check it yourself

• Prophylactic anticonvulsant treatment not indicated