I’m experiencing formication (ants‑crawling sensation) over my body that occurs before a seizure; is this an ictal prodrome of temporal‑lobe epilepsy and what is the appropriate work‑up and treatment?

Formication as an Ictal Aura: Diagnosis and Management

Formication (the sensation of ants crawling on the body) occurring before a seizure represents a somatosensory aura that strongly localizes to the contralateral parietal cortex or, less commonly, the temporal lobe, and requires video-EEG monitoring to confirm the epileptogenic zone followed by high-resolution MRI to identify structural lesions such as focal cortical dysplasia. 1

Understanding Formication as a Seizure Aura

Formication is classified as an elementary sensory seizure symptom that arises from hypersynchronous neuronal discharge in specific cortical regions responsible for cutaneous sensation. 1 When this sensation occurs consistently before loss of consciousness or other seizure manifestations, it functions as an epileptic aura—the initial subjective symptom of a focal seizure. 2

Key Localizing Features

• Somatosensory auras (including formication) typically originate from the parietal cortex contralateral to the side of the body experiencing the sensation, though temporal lobe involvement can also produce cutaneous sensory hallucinations. 1
• The stereotypic nature of your symptoms—occurring repeatedly in the same pattern before seizures—is characteristic of focal epilepsy and provides crucial localizing information. 2
• Temporal lobe epilepsy classically presents with a sequence of aura → behavioral arrest → blank stare → automatisms, though the specific aura type varies based on the exact cortical circuit involved. 2

Critical Diagnostic Work-Up

Essential First-Line Testing

• Video-EEG monitoring is the gold standard and should capture a typical episode showing epileptiform activity over the suspected cortical region. 2 This has revolutionized diagnosis and is mandatory when the diagnosis remains uncertain. 2
• Perform video-EEG at least 24 hours after focal aware seizures and 48 hours after focal impaired awareness or focal-to-bilateral tonic-clonic seizures to optimize interictal findings. 3
• High-resolution epilepsy-protocol MRI (3T preferred) must be obtained to identify structural causes including focal cortical dysplasia, hippocampal sclerosis, or subtle tumors that are common in focal epilepsy. 3, 4

Advanced Imaging When Indicated

• Interictal [18F]FDG PET shows hypometabolism in the epileptogenic zone with 73% sensitivity and 75% specificity, and should be performed at least 24-48 hours after the last seizure. 3
• Ictal SPECT with SISCOM (subtraction ictal SPECT co-registered to MRI) demonstrates hyperperfusion in the seizure focus during an event and has >90% sensitivity in temporal lobe epilepsy, making it valuable for surgical planning. 3
• These nuclear medicine studies are particularly useful when MRI is negative but clinical suspicion for focal epilepsy remains high. 3

Important Differential Considerations

Rule Out Drug-Induced Formication

• Anti-Parkinsonian agents are the most common medication class causing tactile hallucinations including formication, followed by antidepressants, prescription stimulants, antihypertensives (especially propranolol), and antiepileptic drugs themselves. 5
• Medications that alter dopamine, norepinephrine, and serotonin neurotransmission are particularly implicated. 5
• Obtain a complete medication history including over-the-counter drugs and recent changes in dosing. 5

Distinguish from Syncope

• Duration matters: Loss of consciousness <30 seconds strongly favors syncope over seizure, while >1 minute suggests epilepsy. 6, 7
• Post-event state: Confusion or sleepiness lasting more than a few minutes after regaining consciousness points definitively to epilepsy rather than syncope. 3, 7
• Movement timing: In epilepsy, abnormal movements (tonic posturing, clonic jerks) can occur before the fall, whereas in syncope, myoclonic jerks occur after the patient has collapsed due to cerebral hypoperfusion. 3, 7

Treatment Approach

Medical Management

• Initiate appropriate antiepileptic medication based on seizure type once epilepsy is confirmed by video-EEG. 2
• For focal epilepsy with somatosensory auras, treatment selection should be guided by the specific epilepsy syndrome identified. 4
• Monitor for medication-induced formication as a paradoxical side effect, particularly with antiepileptics that modulate dopaminergic pathways. 5

Surgical Evaluation

• All patients with drug-resistant focal epilepsy (failure of adequate trials of two appropriately chosen antiepileptic drugs) should be referred for surgical evaluation. 2, 8
• Patients with lateralizing auras (including unilateral formication) have significantly better surgical outcomes than those without localizing features. 9
• Anterior temporal lobectomy or focal cortical resection can abolish seizures in most patients with well-localized epileptogenic zones. 2, 8
• SISCOM concordance with the surgical resection site predicts a 3-fold higher odds of seizure freedom postoperatively. 3

Critical Pitfalls to Avoid

• Do not dismiss formication as purely psychiatric without thorough epilepsy evaluation—it is a recognized ictal phenomenon. 1
• Do not assume all tactile hallucinations are seizure-related—always review medications and consider drug-induced causes. 5
• Do not delay surgical referral in drug-resistant cases—temporal lobe epilepsy surgery is seriously underutilized despite excellent efficacy and safety. 8
• Do not rely on routine EEG alone—video-EEG monitoring is essential for capturing ictal events and confirming the diagnosis. 2