NAC OSCE Headache Case: Thunderclap Presentation
A 32-year-old female presents with the sudden onset of the worst headache of her life during exercise. Complete station walkthrough — candidate instructions, red-flag assessment, SAH differential, CT-then-LP investigation pathway, and patient counselling.
Station Overview
Station type: History-taking and management. This station tests your ability to identify a potentially life-threatening secondary headache — specifically subarachnoid hemorrhage — in a young patient who may appear deceptively well. Missing the diagnosis in this scenario carries enormous consequences and is a key NAC OSCE teaching case.
Competencies assessed: History taking (red-flag identification), diagnosis (ruling out dangerous cause), investigations (knowing the CT-negative / LP pathway), management, communication.
Key focus: The critical mark in this station is recognising that a normal CT does not rule out SAH. Candidates who stop after a "negative CT" and reassure the patient fail the station. The LP at 6 hours (for xanthochromia) is the key differentiating knowledge point.
Candidate Instructions
Setting: Emergency department, Community Hospital
Ms. Jennifer Park, 32 years old, was brought in by her partner after developing a sudden severe headache while at the gym approximately 2 hours ago. She describes it as the worst headache she has ever had. She has never had a headache like this before. She is alert and oriented.
Your tasks:
1. Take a focused history from Ms. Park.
2. Perform a focused neurological examination (describe what you would do).
3. Outline your investigations and management plan.
The physician examiner will ask you questions at the end of the encounter.
Clinical Approach
Opening — acknowledge severity first
"Ms. Park, I'm Dr. [Name], the emergency physician. I can see you're in a lot of pain — I want you to know we're going to take this very seriously. Your partner did the right thing bringing you in. I'm going to ask you some questions and then examine you. Is that okay?"
The single most important question
Ask this within the first 90 seconds — before SOCRATES:
"When you say it was the worst headache of your life — did it come on suddenly, like a clap or an explosion, or did it build up gradually over minutes or hours?"
A thunderclap onset (maximal intensity within seconds) is the defining feature of SAH. If present, this must drive the entire management plan regardless of subsequent history.
Focused history — SOCRATES with red-flag emphasis
- Site: Diffuse or occipital predominance (SAH); unilateral with aura (migraine)
- Onset: Thunderclap (within seconds — SAH) vs. gradual build over 20–30 minutes (migraine)
- Character: Explosive, bursting — "like something burst in my head"
- Radiation: Neck pain or stiffness (meningism — SAH or meningitis)
- Associations: Nausea/vomiting, photophobia, phonophobia, loss of consciousness (even briefly), focal neurological symptoms, fever
- Prior headache history: Previous migraines? This headache different from usual migraines?
- Triggers: Exertion, Valsalva, sexual activity (all can precipitate SAH from aneurysm rupture)
- Medications: OCP (thrombotic risk), anticoagulants, analgesics (medication overuse)
- Family history: Polycystic kidney disease, connective tissue disorders (associated with cerebral aneurysms)
Focused neurological examination (describe to examiner)
- GCS and level of consciousness
- Pupil reactivity (third nerve palsy — posterior communicating artery aneurysm)
- Fundoscopy (papilledema, subhyaloid hemorrhages — Terson syndrome)
- Meningism: neck stiffness, Kernig's sign, Brudzinski's sign
- Focal neurological deficits: cranial nerves, power, reflexes, coordination
- Blood pressure (hypertensive emergency as a cause)
If the examiner provides you with a "normal CT head" mid-station, do NOT reassure the patient. The correct response: "A normal CT does not rule out subarachnoid hemorrhage — I would proceed with a lumbar puncture to look for xanthochromia, ideally performed at least 6 hours after headache onset." This is the highest-value knowledge point in this station.
Differential Diagnosis
| Diagnosis | Supporting features | Distinguishing point |
|---|---|---|
| Subarachnoid hemorrhage (SAH) | Thunderclap onset, exertional trigger, neck stiffness, worst-ever headache, young adult | Must rule out first — CT then LP at ≥6h |
| Bacterial meningitis | Fever, meningism, gradual onset over hours, photophobia | Fever and infectious prodrome help distinguish; LP needed for both |
| Migraine with aura | Unilateral, throbbing, photophobia, prior similar episodes, aura | Thunderclap onset, exertional trigger, and "worst ever" argue strongly against migraine as a diagnosis of exclusion |
| Hypertensive emergency | Severe hypertension, fundoscopic changes, encephalopathy | Check BP immediately; may coexist with SAH |
| Cerebral venous thrombosis | OCP use, hypercoagulable state, focal deficits, papilledema | MRV or CT venography required if suspected |
Management — SAH Investigation Pathway
Investigations
- Non-contrast CT head — immediately; sensitivity 98% within 6h of onset, drops to 85–90% at 24h
- Lumbar puncture — if CT is negative, perform LP at ≥6 hours post-onset; look for xanthochromia (CSF yellow colour from RBC breakdown) and elevated RBC count that does not clear between tubes 1 and 4
- CT angiography of circle of Willis — if SAH confirmed, to identify aneurysm location
- CBC, coagulation screen, electrolytes, group and screen, ECG (cardiac dysrhythmias occur in SAH)
If SAH confirmed
- Neurosurgery consult immediately
- ICU/monitored bed — risk of rebleed highest in first 24 hours
- Nimodipine 60 mg PO q4h × 21 days — reduces cerebral vasospasm and improves neurological outcome
- Treat hypertension carefully (target SBP <180 mmHg before aneurysm secured) — avoid hypotension
- Definitive treatment: endovascular coiling (preferred) or surgical clipping of the aneurysm
- Monitor for complications: rebleed, vasospasm (days 3–14), hydrocephalus, SIADH, seizures
- DVT prophylaxis after aneurysm is secured
Counselling the Patient
"Ms. Park, I need to tell you what I'm worried about — and I want to be honest with you because the next steps depend on understanding it clearly."
"The sudden, severe headache you described — starting in seconds during exercise — is a pattern that can sometimes mean bleeding around the brain from a burst blood vessel. We call this a subarachnoid hemorrhage. We're going to do a CT scan of your head right away to look for any sign of bleeding. I need you to know that even if the CT looks normal, that doesn't completely rule it out — we'd need to do a second test, a lumbar puncture, to check the fluid around the brain and spine. We'll do that about 6 hours after your headache started."
"I know this is very frightening to hear. Your partner can stay with you. We're monitoring you closely, and if the tests confirm bleeding, the brain specialists will be involved immediately to plan the next steps. Is there anything you'd like to ask me right now?"
This is a "breaking bad news" adjacent station. Use the SPIKES framework: Set up (private space, sit down), Perception (what does she already know/fear?), Invitation ("Are you okay if I share what I'm thinking?"), Knowledge (explain clearly, no jargon), Emotions (pause after the diagnosis, acknowledge), Strategy (what happens next). You will not complete all six steps in 11 minutes — but demonstrating the first four earns communication marks.
This is a practice case based on a station from NAC OSCE: A Comprehensive Review (2nd Edition). The full book version includes a detailed patient history, physical examination findings, an expanded differential diagnosis, step-by-step management aligned to Canadian guidelines, and a complete counselling script — across all 92 stations.