QUESTIONS and CONTROVERSIAL ISSUES

I) What is the differential diagnosis for toxic seizures?

• O= Organophosphates
• T= Theophylline
• I= INH, Insulin
• S= Sympathomimetics, Salicylates
• C= Camphor, Cocaine
• A= Antidepressants
• M= Methyl xanthines
• P= PCP
• B= Beta Blockers
• E= Ethanol withdraw
• L= Lead, Lithium
• L= Lidocaine, Lindane

II) How should this patient's intractable seizure activity be managed?

1. Benzodiazepines
2. Phenobarbital
3. Phenytoin
4. General anesthesia
5. R/O metabolic etiology / CNS space-occupying lesion
6. Pyridoxine (vitamin B6)
7. ---Replenishes GABA neurotransmitter stores depleted by isoniazid toxicity
8. ---Dose- match gram for gram to the amount of INH ingested; if unknown, start with 5 gms
9. ---Isoniazid toxicity should be suspected in any patient with intractable seizures and profound metabolic acidosis with elevated anion gap

CLINICAL COURSE

The patient suffers more seizure activity in the ED despite benzodiazepines, phenytoin, phenobarbital and oral intubation. Further information from the prison infirmary reveals the patient has a past medical history of TB and is presently being treated with isoniazid (INH). Following administration of 10gm of pyridoxine (Vitamin B6) the seizure activity abates and metabolic acidosis resolves.