The Diagnostic Journey: Finding the Source

Diagnosing focal sensory seizures is often a process of “clinical detective work.” Because the symptoms are internal and you remain fully aware, your personal account of the event is the most important piece of evidence. This page explains the diagnostic pathway, the specialized tests used to look for “electrical storms,” and why a normal test result doesn’t always mean the seizures aren’t happening.

The Clinical Foundation: Your Story

The diagnosis of focal epilepsy is often clinically led ^[1]. This means your doctor uses your detailed description of the sensation—its “flavor,” where it starts, and how it spreads—to build a map of where the seizure might be occurring ^[2]. This “story” is incredibly important. However, a compelling story is not proof of epilepsy; if tests are normal, clinicians must also review other possibilities like migraines, functional or dissociative episodes, panic attacks, metabolic issues, or peripheral nerve disorders. Even if every scan is normal, a highly consistent and specific sensory pattern (like a “Jacksonian march”) can lead to a diagnosis ^[1].

EEG: Catching the Electrical Storm

An EEG (electroencephalogram) records the electrical activity of your brain using sensors on your scalp.

Why Routine EEGs Can Be Normal

It is common for a routine, 20-minute EEG to come back “normal.” This happens for several reasons:

• Timing: A routine EEG is just a snapshot. If you don’t have a seizure or “hidden” electrical spikes during those 20 minutes, the test will look normal ^[3].
• Depth: Scalp sensors are best at detecting activity on the brain’s surface. Small, brief, or deep seizures—typical of some sensory types—may not create a strong enough signal to reach the scalp sensors ^[4][5].
• Awareness: In one study, scalp EEG detected only 33% of “aware” seizures, compared to 97% of those where awareness was lost ^[4]. (These figures reflect that specific study group, not your personal probability).

A normal EEG simply means the test did not show diagnostic abnormalities; it does not automatically rule out epilepsy, but it does require careful clinical judgment.

Beyond the Routine EEG

If a routine test is unrevealing, your doctor may suggest:

• Sleep-Deprived EEG: Lack of sleep can “activate” abnormal brain waves, making them easier to catch ^[6].
• Ambulatory or Video-EEG: You may wear a portable EEG for 24–72 hours or stay in an Epilepsy Monitoring Unit (EMU) for several days. In people with focal epilepsy whose routine EEGs were normal, one study found a 4-to-5-day video-EEG captured seizures in nearly 58% of cases ^[7].

MRI: Mapping the Brain’s Structure

While EEG looks at the brain’s “software” (electricity), an MRI looks at the “hardware” (structure). A standard MRI may miss the tiny changes that cause epilepsy. Instead, doctors use a dedicated epilepsy-protocol MRI (such as the HARNESS-MRI protocol, as one high-quality example) ^[8].

What They Look For

Radiologists look for subtle structural triggers, including:

• Focal Cortical Dysplasia (FCD): A small area where brain cells didn’t form correctly during development ^[9].
• Hippocampal Sclerosis: Small scars or shrinkage in the hippocampus, a deep part of the brain often involved in seizures ^[10].
• Vascular Malformations: Unusual clusters of blood vessels ^[11].

Repeat imaging is highly individualized, often based on the quality of the first study or if you develop new neurological findings. There is no universal repeat schedule.

Understanding Your Reports

Medical reports use specific terms to describe findings. Here is what they generally mean:

Completeness Checklist

A comprehensive diagnostic workup for focal sensory seizures should ideally include:

1. Meticulous History: A clinical review of your sensory “semiology” (symptom pattern) ^[1].
2. Standardized MRI: Specifically asking for an “Epilepsy Protocol” with 3D T1, 3D FLAIR, and high-resolution T2 sequences ^[8].
3. Extended EEG: If routine results are normal and diagnosis is uncertain, moving to sleep-deprived or multi-day monitoring ^[7][6].
4. Expert Review: Having your scans and tracings read by a board-certified epileptologist or an epilepsy-trained neuroradiologist ^[8].

If your initial tests are normal but your symptoms persist, don’t be discouraged. A “normal” test often just means more specialized tools—and more of your expert testimony—are needed to find the source of the storm ^[7].