CONVULSIONS
DEFINITIONS
1. Acute generalized convulsion: paroxysmal discharge of cerebral
neurons resulting in a brief clinical phenomenon characterized by
loss of consciousness and generalized involuntary tonic and
clonic contractions of the skeletal muscles.
2. Acute focal convulsion: paroxysmal discharge of localized central
neurons (e.g. petit mal, temporal, focal motor).
3. Status epilepticus: continued unremitting convulsions or several
consecutive episodes without intervening restoration of
consciousness.
TOXIC CAUSES
Pharmaceuticals
Antihistamines
Camphor
Carbamazepine
Carbon monoxide
Chlorambucil
Cyclic antidepressants
Cyclosporine
Ergot alkaloids
Hypoglycaemic agents
Isoniazid
Lithium salts
Local anaesthetics
Mefenamic acid
Metronidazole
Nicotine
Penicillin
Pentazocine
Pethidine (meperidine)
Phenothiazines
Physostigmine
Propoxyphene
Salicylates
Xanthine derivatives (theophylline, caffeine)
Drugs of abuse
Amphetamines and derivatives (e.g. MDMA/"ecstasy")
Cocaine
PCP (phencyclidine)
Pesticides
Carbamates
Organochlorines
Organophosphorus compounds
Strychnine
Others
Hyperbaric oxygen
Ethanol and sedative-hypnotic drug withdrawal syndrome
Heavy metals (e.g., lead in children)
NON-TOXIC CAUSES
Structural
Haemorrhage
Tumour
Trauma
Non-structural
Cardiac arrhythmia
Fever
Hypoxia
Hypoglycaemia
Infection
Metabolic
CLINICAL FEATURES
Toxic convulsions are characterized by generalized involuntary tonic
and clonic contractions of skeletal muscles. There may be evidence of
physical injury (e.g.: tongue biting) and/or incontinence. The
post-convulsive state may be associated with coma or altered CNS
function ("Todd's paralysis").
Acute complications may include pulmonary aspiration of gastric
contents, hypoventilation, hypoxia, metabolic acidosis, cardiac
arrhythmias, rhabdomyolysis, and sudden death.
DIFFERENTIAL DIAGNOSIS
Abnormal movements (dyskinesia, myoclonic jerking, dystonic reactions)
Muscular hyperactivity and/or rigidity
Malingering, hysteria (pseudoseizures)
Tetany or tetanus
Fasciculations due to organophosphorus or carbamate poisoning
RELEVANT INVESTIGATIONS
The following investigations should be performed routinely:
Blood glucose
Serum electrolytes including calcium
Additional tests that may be clinically relevant include:
Arterial blood gases
Cerebrospinal fluid analysis
Creatine phosphokinase
CT Scan head
EEG
Serum magnesium
Serum anticonvulsant concentrations
Toxicological screening.
TREATMENT
Most toxic convulsions are brief, lasting from a few seconds to a few
minutes, and usually do not require pharmacological intervention.
However, if the seizure is prolonged, or if status epilepticus
supervenes, urgent medical intervention is required. Status
epilepticus is an acute medical emergency. Suggested treatment
protocols for adults and children are as follows:
Initial Management
Protect patient from self-inflicted injury; remove false teeth if
present; establish a clear airway and give high flow oxygen by mask.
Place the patient in lateral semiprone position. Establish
intravenous access.
Glucose. If rapid bedside glucose measurement indicates low blood
sugar, administer intravenous glucose (adults: 25 g IV; children:
0.5 to 1 g/kg IV, as 25% dextrose).
Benzodiazepines: (Note - patients should be carefully monitored for
evidence of respiratory depression and hypotension during
administration.)
1. Give Diazepam 10 mg intravenously (0.15 to 0.25 mg/kg) over
1 minute. If convulsions continue, give a further 10 mg over 1
minute. This may be repeated if necessary. Diazepam may be
given IM, but absorption is erratic and this route is not
recommended. Rectal administration has been used in children
(0.5 mg/kg) when IV access is not readily available.
2. Lorazepam (0.1 mg/kg IV at 1 to 2 mg/minute up to a maximum of
10 mg) or Clonazepam (0.5 to 1mg IV) may be used instead of
diazepam. Also consider midazolam, which is rapidly absorbed
after intramuscular administration (IM dose: 0.1-0.2 mg/kg).
If convulsions are difficult to control with large doses of
benzodiazapines, the following drugs may be considered:
Phenobarbitone (Phenobarbital) 15 mg/kg intravenously slowly (e.g.
2 mg/kg/min). Repeat doses may be given, up to a total dose of
30 mg/kg. Monitor blood pressure and heart rate during infusion.
Hypotension may occur. Observation of respiratory state is mandatory
and assisted ventilation may be required.
Phenytoin. As an alternative to phenobarbitone, administer
phenytoin 15 to 20 mg/kg body weight IV in 0.9% normal saline (1 g
in 250 mL), to be given no faster than 50 mg/kg/minute. Monitor
cardiac rhythm and blood pressure. Rapid infusion of intravenous
phenytoin may cause acute hypotension, AV block, or asystole. (Note:
phenytoin is not effective for patients with seizures caused by
theophylline and may be dangerous in patients with tricyclic
antidepressant overdose).
Thiopentone. If control of convulsions is not achieved with the
preceding drugs, general anaesthesia with thiopentone should be
instituted (adult dose: 500mg diluted in 20 mL administered
intravenously over 2 to 3 minutes or until the convulsion stops.
Consider maintenance infusion at 2 to 4g/24hrs). Mechanical
ventilation is required, and heart rate and blood pressure should be
monitored.
Note: If neuromuscular relaxants are given to control muscular
hyperactivity, EEG monitoring must be instituted because CNS seizures
may continue without external manifestations.
Pyridoxine. If isoniazid overdose is suspected, administer
Pyridoxine, 1g IV for each gram of isoniazid ingested (or 4 to 5g IV
empirically).
Thiamine. In alcoholic or malnourished patients, consider
Thiamine 100 mg IV or IM.
CLINICAL COURSE AND MONITORING
Toxic seizures are usually self-limited. Monitoring of vital signs
and neurological status is required until the patient is fully
conscious and convulsion-free.
LONG-TERM COMPLICATIONS
Permanent neurologic deficit may result from prolonged convulsions or
acute respiratory failure and hypoxia.
AUTHOR(S)/REVIEWERS
Authors: Poisons Unit, London, United Kingdom.
Reviewers: Sao Paulo 9/94, Cardiff 3/95, Berlin 10/95; Cardiff
9/96: V. Afanasiev, M. Burger, T. Della Puppa,
L. Fruchtengarten, K. Olsen, J. Szajewski).