From the Guidelines
Normal serum lactate levels cannot be used to definitively rule out true seizures from non-true seizures. The provided evidence does not directly address the use of serum lactate in differentiating between true and non-true seizures, but it does discuss the limitations of lactate measurements in other contexts, such as bacterial meningitis 1. In the context of seizures, elevated serum lactate (typically >2.0 mmol/L) is often seen following true epileptic seizures due to intense muscle activity and temporary hypoxia, causing a shift to anaerobic metabolism. However, normal lactate levels do not definitively rule out a true seizure, as levels can normalize quickly (within 1-2 hours post-seizure) or may not rise significantly in brief seizures.
Some key points to consider when evaluating seizures include:
- The classification of seizures by the International League Against Epilepsy (ILAE) was last revised in 2017 1
- Seizures are classified as focal onset, generalized onset, or unknown onset 1
- Focal seizures can be further characterized by having motor onset or nonmotor onset symptoms and can also be characterized by being aware or having impaired awareness 1
- Generalized seizures rapidly affect both hemispheres as well as both sides of the body, even when caused by a “focal” lesion 1
For accurate diagnosis, clinicians should use a comprehensive approach that includes:
- Clinical history
- Eyewitness accounts
- Video recordings when available
- Electroencephalography (EEG)
- Neuroimaging studies Serum lactate is best viewed as one piece of supporting evidence rather than a definitive diagnostic tool in distinguishing epileptic from non-epileptic events.
From the Research
Serum Lactate and Seizure Diagnosis
- Serum lactate levels can be used to differentiate between generalized tonic-clonic seizures (GTCS) and other forms of Transient Loss of Consciousness (TLOC) 2.
- A study found that serum lactate levels were significantly higher in patients with GTCS compared to those with other forms of TLOC, including psychogenic nonepileptic seizures (PNES), syncope, and non-GTCS 2.
- The study suggested that a serum lactate concentration of 2.4 mmol/L could be used to differentiate between GTCS and non-GTCS, with an area under the receiver operating curve (AUROC) ranging from 0.94 to 0.97 2.
Limitations of Serum Lactate
- Serum lactate levels should not be used as an absolute diagnostic tool, but rather interpreted in the context of clinical presentation and other diagnostic tests 2.
- There was no significant difference in serum lactate levels between syncope, PNES, and non-GTCS, making it less useful for distinguishing between these conditions 2.
Comparison to Other Studies
- Other studies have focused on the treatment of status epilepticus, including the use of benzodiazepines such as lorazepam and diazepam 3, 4, 5.
- A meta-analysis found that intravenous lorazepam was more effective than intravenous diazepam for the cessation of adult status epilepticus 5.
- However, these studies do not provide direct evidence for the use of serum lactate in ruling out true seizure from non-true seizure.