A 40 year old male with a past medical history of polysubstance use, epilepsy, and housing insecurity presents to the emergency department for drug intoxication. His ED course is uncomplicated, and he is deemed ready for discharge 3 hours after his initial presentation. Upon handing him his discharge paperwork, he appears to trip and fall to the ground. He then demonstrates diffuse shaking of his entire body with his eyes tightly shut, not responding to external stimuli. The episode lasts approximately 2 minutes, and he afterward remains unresponsive to stimuli. Vital signs and point-of-care glucose are within normal limits. Physical exam shows no obvious injuries. Which of the following laboratory tests is most helpful in determining if the patient had an epileptic seizure?
A: Creatine kinase
B: Lactic acid
C: Potassium
D: White blood cell count
Answer: Lactic acid
Distinguishing between true epileptic seizures, psychogenic non-epileptic seizures (PNES), and convulsions following a syncopal episode can be difficult. PNES is psychogenic in nature and has highly variable features which may include forceful closing of the eyelids, side-to-side movements, or shrieking. An elevated serum lactic acid concentration obtained shortly after the event has been shown to help differentiate true epileptic seizures from PNES or convulsions following syncope. Creatine kinase levels typically do not rise early after a seizure and are furthermore not specific in the setting of falls or trauma. Potassium levels are not expected to be elevated following an uncomplicated seizure. An elevated white blood cell count may be due to several non-specific reasons including infection, trauma, steroid use, or stress response. Definitive diagnosis is determined using electroencephalography (EEG).
References:
Kornegay J. Seizures and Status Epilepticus in Adults. In: Tintinalli JE, Ma O, Yealy DM, Meckler GD, Stapczynski J, Cline DM, Thomas SH. eds. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 9e. McGraw-Hill Education; 2020.
Patel J, Tran QK, Martinez S, Wright H, Pourmand A. Utility of serum lactate on differential diagnosis of seizure-like activity: A systematic review and meta-analysis. Seizure. 2022;102:134-142. doi:10.1016/j.seizure.2022.10.007
