Recognizing Symptoms and Emergency Warning Signs

The symptoms of Primary Angiitis of the Central Nervous System (PACNS) are notoriously difficult to pin down because they often mimic other conditions and vary significantly from person to person. Because the disease attacks blood vessels in the brain and spinal cord, the symptoms depend entirely on which vessels are affected and how much blood flow is being restricted ^[1][2].

Red Flags: When to Seek Emergency Care

While many PACNS symptoms are gradual, the disease can cause sudden, life-threatening complications. If you or a loved one notices any of the following “red flag” symptoms, call emergency services immediately. Do not wait for a routine specialist appointment.

• Sudden “Thunderclap” Headache: An excruciating headache that reaches its peak intensity within seconds or minutes. This requires immediate emergency assessment as it can indicate a subarachnoid hemorrhage (bleeding in the brain), Reversible Cerebral Vasoconstriction Syndrome (RCVS), or other emergencies ^[3][4]. (Note: A headache’s response to over-the-counter medicine cannot distinguish a safe headache from a dangerous one).
• Sudden Focal Deficits: Use the BE FAST acronym: Balance loss, Eye/vision changes, Facial drooping, Arm weakness, Speech difficulty, Time to call emergency services ^[2][4].
• New or Prolonged Seizures: Any first-time seizure, or a seizure that lasts more than five minutes or happens repeatedly without the person waking up in between ^[5].
• Rapid Decline in Consciousness: Becoming suddenly very drowsy, impossible to wake up, or profoundly confused ^[6].
• Signs of High Brain Pressure: Worsening headache combined with repeated vomiting, unequal pupil sizes, or extreme sleepiness ^[6][7].

How PACNS Usually Begins

Unlike a typical stroke that happens in an instant, PACNS often has an insidious onset, meaning it develops gradually and quietly over weeks or even months ^[8][9]. You might first notice a persistent, dull headache or subtle changes in your ability to think clearly before more obvious neurological problems appear.

Research into hundreds of cases shows that at the time of diagnosis, the most common symptoms are:

• Focal Neurological Deficits (63% to 83%): These are problems with specific body functions, such as weakness on one side, numbness, or difficulty speaking ^[1][2].
• Headache (51% to 53%): This is often described as a new, persistent, or worsening headache that doesn’t go away with typical over-the-counter treatments ^[1][2].
• Cognitive Dysfunction (40% to 41%): This can feel like “brain fog,” memory loss, confusion, or a change in your personality or behavior ^[1][2].
• Seizures (18% to 38%): New-onset seizures can be a primary symptom, especially in cases where the inflammation affects smaller blood vessels or irritates the cortex ^[2][3][10].

Understanding the Symptom Groups

Because PACNS is a “patchy” disease, your experience will fall into one or more of these categories based on how the inflammation is affecting your brain tissue.

Ischemic Events (Strokes and TIAs)

When inflammation narrows a blood vessel, it can block blood flow entirely, leading to an ischemic stroke (brain tissue death) or a TIA (transient ischemic attack, often called a “mini-stroke”). This is most common in medium-to-large vessel disease ^[11]. You might experience sudden weakness, facial drooping, or loss of vision.

Cognitive and Affective Changes

In small-vessel PACNS, the damage is often more widespread and subtle ^[11]. Instead of a single major stroke, you might experience encephalopathy—a general term for altered brain function. This can show up as becoming increasingly sleepy, confused, or losing the ability to perform complex tasks like managing finances or following a recipe ^[12].

Seizures

Seizures occur when the inflammation irritates the surface of the brain (the cortex). While some people have a single seizure, others may experience repeated episodes that require intensive medical management ^[5][10].

The Challenge of Overlap

It is important to remember that these symptoms overlap with many other conditions, including infections, other autoimmune diseases, and even certain types of cancer ^[13][14]. This is why your doctors use a combination of MRI scans, spinal taps, and sometimes biopsies to ensure they are treating PACNS and not something else. Not every headache is a stroke, but in the context of PACNS, new or changing symptoms always warrant a prompt conversation with your neurology team.