Why Do Symptoms Fluctuate in Autoimmune Encephalitis?

When a loved one with seronegative autoimmune encephalitis has symptoms that get dramatically better and worse within the same day, it can be confusing and terrifying. It is common to wonder if the person is controlling their behavior intentionally. “Seronegative” means that a disease-specific antibody was not detected on tests, but the illness and the brain injury are very real ^[1].

While overall brain inflammation can change over weeks or months ^[2], rapid hour-to-hour fluctuations are not usually a sign that the immune system is “turning on and off” by the minute. Instead, these daily swings have several possible overlapping contributors, including seizures, sleep-wake disruption, cognitive fatigue, medication effects, and delirium. Because the brain networks responsible for awareness and behavior are injured, they are highly sensitive to these stressors.

Emergency Warning Signs

Do not wait for a scheduled neurology appointment or an outpatient EEG if you see signs of a medical emergency. Call emergency services or go to the nearest emergency department if the person experiences:

• A convulsive seizure lasting more than 5 minutes, or repeated seizures without recovering awareness in between ^[3][4]
• Inability to be awakened or severe difficulty arousing them ^[5]
• Breathing pauses, blue lips, or obvious difficulty breathing ^[4]
• A new focal neurological deficit, such as sudden one-sided weakness or facial drooping ^[6]
• Rapidly worsening confusion accompanied by fever or neck stiffness ^[7]

What to Do During a Fluctuating Episode

If the person is having a sudden change in awareness or a suspected seizure, focus on safety:

• Keep them safe from falls or sharp objects.
• Note the exact start and stop time.
• Do not restrain them or put anything in their mouth.
• Do not give food, liquids, or oral medications if they are too drowsy to swallow safely.
• If safe and respectful of privacy, take a short video to show the neurologist.

Possible Contributors to Daily Fluctuations

Focal and Nonconvulsive Seizures
Autoimmune encephalitis can cause seizures, and the frequency varies depending on the specific disease subtype and individual ^[8]. While most people picture convulsions, seizures can also be “focal” (affecting one part of the brain) or “nonconvulsive” ^[9]. During these episodes, abnormal electrical activity in the brain causes sudden changes without obvious physical shaking ^[10]. This can look like sudden confusion, staring blankly, interrupted speech, aphasia (inability to speak or understand words), unusual eye movements, or automatisms (repetitive movements like lip-smacking or picking at clothes) ^[9]. These episodes can start and stop, causing awareness to appear to fluctuate.

Cognitive Fatigue and Sleep Disruption
The brain requires energy to function, and an inflamed or healing brain depletes its cognitive reserves quickly ^[11]. A patient might have the mental energy to hold a conversation in the morning but become confused or irritable later in the day due to cognitive fatigue ^[12]. Furthermore, sleep disruption is common in autoimmune encephalitis ^[13]. Poor sleep can significantly worsen attention and alertness. In some cases, sleep-related breathing disorders like hypoventilation (shallow or slow breathing) or sleep apnea can occur ^[14], preventing restorative sleep and contributing to daytime fluctuations.

Medication Effects
The medications used to manage the illness can also alter behavior and awareness. Anti-seizure medications can sometimes cause behavioral side effects like irritability, mood changes, or agitation ^[15]. Sedatives or calming medications can cause heavy drowsiness that shifts as the medication enters and leaves the body ^[16]. Never stop anti-seizure medications, steroids, or other prescribed treatments abruptly without medical advice, as sudden withdrawal can trigger severe seizures or a relapse ^[17].

Delirium and Metabolic Changes
Injured brains are highly susceptible to delirium—an acute, fluctuating state of confusion and altered attention triggered by physical stress outside the brain ^[18]. Delirium can be triggered by clinical infections, dehydration, constipation, low oxygen (hypoxia), glucose abnormalities, or electrolyte imbalances like hyponatremia (low blood sodium) ^[19].

Changes in Inflammation
While hour-by-hour changes are usually driven by other factors, the underlying inflammation can fluctuate over the broader course of the disease, sometimes worsening during immunotherapy tapers ^[2]. However, treatment decisions require the medical team to look at the whole picture; patients should not alter their immunotherapy doses on their own.

The Role of Medical Reassessment and EEG

Because fluctuations can have many causes, clinical evaluation is needed to distinguish them. Do not dismiss changes as purely psychiatric or intentional ^[20].

If nonconvulsive seizures are suspected, your neurologist may order an EEG (electroencephalogram) to measure the brain’s electrical activity ^[21]. A routine 30-minute EEG can sometimes miss intermittent seizures ^[22]. Depending on the clinical picture, the medical team may order a prolonged, ambulatory, or continuous video-EEG to get a better look ^[23]. However, normal EEG results do not completely rule out seizures, and the appropriate duration of monitoring is individualized.

To help your doctor figure out the pattern, keep a simple symptom diary. Record the time, duration, exact behavior, meal and medication times, sleep quality, and how the person recovered. This gives the medical team the vital clues they need to adjust the care plan safely.